Abstract

High crystallinity GeSn substitutional alloy thin films with up to 8.7 at.% Sn are directly grown on amorphous SiO2 layers at low crystallization temperatures of 370~470 °C for potential applications in 3D electronic-photonic integration on Si as well as inexpensive virtual substrates for tandem solar cells. The optimal Ge0.913Sn0.087 thin film demonstrates a strong (111) texture and an average gain size of 10 μm, and its grain boundaries are mostly twin and low-angle boundaries with low densities of defect recombination centers. The 8.7 at.% Sn incorporated substitutionally into the Ge lattice far exceeds the ~1 at.% equilibrium solubility limit. Correspondingly, the direct band gap is significantly red-shifted from 0.8 eV for pure Ge to ~0.5 eV for crystalline Ge0.913Sn0.087, right at the verge of the indirect-to-direct gap transition that occurs at 8-10 at.% Sn alloying. Optoelectronic properties are greatly enhanced due to this transition.

© 2013 Optical Society of America

1. Introduction

Growing high crystallinity (i.e. single crystal or large-grained) semiconductor thin films directly on amorphous materials has long been a significant challenge in materials science, which, once accomplished, could break through the limitations of epitaxy and wafer bonding. This technology is of great importance for large-area semiconductor devices such as thin film solar cells and flat panel display. Moreover, it also enables novel circuit architectures such as 3D electronic-photonic integration on Si microchips, which combines the merits of photons in high bandwidth, energy-efficient data transmission with those of electrons in high-speed data processing for future generations of information and communication technologies [15].

Crystalline Ge plays an important role in advanced optoelectronics, such as Si-based electronic-photonic integration and high-efficiency tandem solar cells, due to its desirable optoelectronic properties, compatibility with Si complementary metal oxide semiconductor (CMOS) processing, and lattice matching with III-V semiconductors of different band gaps. For example, in integrated Si photonics, Ge has been applied to photodetectors [4], modulators [3], and lasers [6] via heteroepitaxy on Si at temperatures >600 °C in front-end-of-line (FEOL) planar integration. In this case, the photonic components are fabricated on the same layer as the CMOS transistors [5]. Growing high crystallinity Ge on amorphous dielectric layers at low temperatures <500 °C can further enable large-scale, 3D photonic integration on Si by moving all the photonic components to the metal/dielectric interconnect level well above the CMOS layer using back-end-of-line (BEOL) processing [5]. This BEOL 3D integration approach is drastically advantageous over FEOL planar integration, because it avoids complicated modifications of the existing CMOS process flow and circumvents the problem of sacrificing CMOS circuit area for much larger photonic components [7,8]. In addition, since the photonic layer is separated from the CMOS layer, this 3D architecture also alleviates the instability issue of photonic devices caused by thermal fluctuations in CMOS circuits [9,10]. In this application, a growth temperature <500 °C is required for compatibility with the metal contacts and interconnects. In another different area of interest, namely tandem solar cells, expensive single crystal Ge wafers are commonly used as substrates for epitaxial growth of III-V solar absorber layers [11]. The costs would be greatly reduced if, again, high crystallinity Ge can be fabricated on low-cost amorphous substrates like glass at <500 °C to avoid softening of the substrates.

Metal-induced crystallization (MIC) has been investigated to improve the crystallinity of Ge and SiGe grown on amorphous layers at low temperatures [1214]. However, the metals commonly used in MIC, including Ni, Au, Co, Ag, Pd and Al, introduce either deep-level defect centers or exceedingly high doping concentrations that are detrimental to semiconductor device performance. Recently, single crystal Ge growth of ~1 μm2 on amorphous Si at 450 °C has been demonstrated using geometrically confined growth [15]. In this approach, however, the shape of the crystal is not well controlled due to faceting, and the lateral growth rate is limited to a few μm/h in order to prevent random Ge nucleation on the SiO2 mask layer.

In this paper, we investigate a new method that incorporates Sn into Ge to enhance crystallization and optoelectronic properties simultaneously. While epitaxial growth of GeSn on single crystalline substrates has been studied in recent years for applications in high-mobility transistors [16] and optoelectronic devices [17,18], growing high crystallinity GeSn directly on amorphous materials has not yet been investigated. By engineering the Sn composition in the as-deposited amorphous GeSn (a-GeSn) thin films, high crystallinity GeSn on SiO2 layers is achieved at low annealing temperatures of 370 °C~470 °C utilizing enhanced crystallization in the Ge-Sn eutectic system. Up to 8.7 at.% Sn is incorporated substitutionally into the lattice of Ge, far exceeding the equilibrium solubility limit of ~1 at.% [19]. Consequently, the direct band gap significantly red-shifts from 0.8 eV for pure Ge to ~0.5 eV for Ge0.913Sn0.087, right at the verge of the indirect-to-direct gap transition that occurs at 8-10 at.% Sn alloying [20,21]. This transition enhances the optical absorption and emission efficiencies substantially. Furthermore, the high crystallinity Ge0.913Sn0.087 thin film is lattice-matched to In0.65Ga0.35P and In0.17Ga0.83As, two ternary semiconductors optimized for triple junction tandem cells [11,22]. Our results indicate that it is promising to achieve near single crystalline GeSn on amorphous layers for applications in both 3D photonic integration on Si and cost-effective tandem solar cells.

2. Principles of Enhanced Crystallization and Optoelectronic Properties in the Ge-Sn System

In this section we will first present the basic principles of eutectically enhanced crystallization in the Ge-Sn system, and then discuss the effect of Sn incorporation on the band structure.

From a materials science point of view, the Ge-Sn system has a great potential to achieve high crystallinity at low processing temperatures due to eutectically enhanced nucleation and growth process. The equilibrium eutectic phase diagram of Ge-Sn is shown in Fig. 1 [19], where the eutectic temperature is 504.1 K (231.0 °C) and the equilibrium solubility of Sn in Ge is ~1 at.% from 500 to 800 K (227 to 527 °C). For overall Sn compositions between 1.5 and 99 at.% in this temperature range, a Ge-rich solid phase (with ~1 at.% Sn) coexists with a Sn-rich liquid phase. During the crystallization process of the a-GeSn thin films upon thermal annealing, which involves rearrangement of atoms into a long-range ordered diamond cubic structure, the Sn-rich liquid phase greatly enhances atomic transport, and subsequently, nucleation and growth of the Ge-rich GeSn solid phase. Hence, the temperature needed for crystallization is expected to be decreased and the crystallinity improved compared to the case of pure Ge. Considering the lower surface energy of Sn than Ge, we also expect that the Sn-rich liquid phase is likely to segregate at the grain boundaries and on the surface [23,24] of the GeSn solid phase. As will be shown in the next section, this hypothesis is confirmed by our experimental results, and the segregated Sn can be selectively removed by adequate chemical etching for device applications.

 

Fig. 1 (a) Ge-Sn equilibrium phase diagram. (b) A zoomed-in diagram on the Ge-rich side [19].

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In the crystallization process of a-GeSn discussed above, the involvement of a liquid phase is somewhat similar to liquid phase epitaxy (LPE) as well as the vapor-liquid-solid (VLS) method for nanowire growth. In fact, in LPE Sn is also used as the melt to grow Ge and GeSn on single crystal substrates [25,26]. The major difference of our approach is that we start with a metastable a-GeSn thin film precursor instead of a GeSn melt at thermodynamic equilibrium. As will be discussed later, this fundamental difference may have led to a much higher substitutional Sn incorporation into the lattice of Ge than the equilibrium solubility limit shown in Fig. 1. The Sn composition in the as-deposited a-GeSn thin film is a critical factor for crystallization: if there is too little Sn, simply there would not be enough liquid phase to enhance atomic transport and crystallization; if there is too much Sn, on the other hand, the nucleation rate could be so fast that there are too many competing nucleation sites to grow large grains. As will be shown later, there is indeed an optimal Sn composition in the as-deposited a-GeSn thin films to achieve the best crystallinity after annealing at temperatures <500 °C, where grain growth prevails over nucleation.

Since Sn is in the same group as Ge, no deep-level defect centers or excess carriers are introduced during the eutectically enhanced crystallization process of a-GeSn thin films, which overcomes a common issue of the conventional MIC process. Furthermore, it has been shown both theoretically and experimentally that alloying Ge with Sn would induce an indirect-to-direct gap transition [20,21,23,27,28]. This transition is due to the fact that the direct gap shrinks much faster than the indirect gap with the increase of Sn composition, which leads to much more efficient optical absorption and light emission for optoelectronic device applications. The Sn composition needed for the indirect-to-direct gap transition is 8-10 at.% [20,21], which is proved to be approachable during the eutectically enhanced crystallization process of a-GeSn by this work.

In summary, alloying Ge with Sn is advantageous over existing methods of growing Ge crystals on amorphous layers since this new approach simultaneously facilitates crystallization at low temperatures and enhances the optoelectronic properties. In the following sections we will present and discuss the experimental procedures and results in detail, demonstrating the effectiveness of our new approach.

3. Experimental

GeSn thin films are deposited by thermal co-evaporation of Ge and Sn in a Lesker Lab 18 physical vapor deposition (PVD) tool. Four-inch Si (100) wafers with 10 nm thermally grown SiO2 are used as the substrates. The inset of Fig. 2(a) shows the schematic cross-section of the samples. The chamber pressure is 10−8 Torr before deposition, and 10−6 Torr during deposition. Nominal deposition rates range from 0.5 to 1.4 Å/s as recorded by a quartz crystal monitor. The concentrations of Sn in the as-deposited a-GeSn thin films range from 4.7 to 16.5 at.%, as determined by energy dispersive X-ray spectroscopy (EDS). A pure Ge thin film is also prepared as a reference. The film thicknesses are determined by cross-sectional scanning electron microscopy (SEM). The film thickness of pure Ge is 100 nm, and that of GeSn with 4.7 at.% Sn is 150 nm. The rest of the GeSn films are ~300 nm thick. All the as-deposited films are amorphous as confirmed by X-ray diffraction (XRD) analyses, regardless of the Sn compositions. After deposition, the wafers are cut into 1.5 × 1.5 cm2 pieces. Some samples are annealed in a horizontal tube furnace with a N2 flow of 8 SCCM, others in a rapid thermal annealing (RTA) furnace. After crystallization annealing at 340~600 °C, a small amount of Sn tends to segregate out of the thin films. Therefore, the Sn compositions in the crystallized GeSn films are decreased compared to the as-deposited amorphous ones. In the following text, we will refer to the Sn compositions of the as-deposited a-GeSn thin films to distinguish the samples, unless otherwise noticed.

 

Fig. 2 (a) θ-2θ XRD data of the GeSn sample with 9.5 at.% Sn annealed at 464°C in comparison to a reference pure Ge sample annealed at 660 °C, both for 30 minutes. Note that the vertical axis is in log scale. The inset shows a schematic cross-section of the GeSn sample. (b) Raman spectra of the unannealed and annealed 9.5 at.% Sn sample in comparison to a single crystal Ge reference sample. (c) Crystallization temperature and XRD peak intensity ratio of the strongest peak (111) to the second strongest peak (either (220) or (311)) as a function of the Sn atomic concentration in as-deposited a-GeSn films. The linear fit shows that the crystallization temperature decreases by ~20 °C with 1 at.% increase in the Sn composition. The strongest (111) textured is achieved at 9.5 at.% Sn.

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The XRD analysis uses Cu Kα line. Raman spectra are measured using an excitation laser emitting at λ = 514 nm. Electron backscatter diffraction (EBSD) mappings are scanned with a resolution of 0.1 μm. Transmittance spectra are measured using a Fourier transform infrared (FTIR) spectrometer.

A 2-min etching in 37.2% HCl:H2O solution is used for the selective removal of Sn segregates on annealed GeSn thin films. To determine the etching rates of pure Sn and Ge-rich GeSn thin films, we partially mask the thin films and create timed etching steps on the samples. The etching step heights are measured using both a profilometer and an optical interference microscope. The results from the two methods are consistent. We determine that the etching rate of Sn is >4 nm/second, whereas that of Ge-rich GeSn is 3 nm/hour, indicating a high etching selectivity of Sn to Ge-rich GeSn > 4800:1.

4. Results and discussion

Figure 2(a) compares the θ-2θ XRD data of the GeSn sample with 9.5 at.% Sn annealed at 464 °C to the pure Ge reference sample annealed at 660 °C, both for 30 minutes. The first observation is that the sample with 9.5 at.% Sn demonstrates a strong (111) texture after crystallization: the (111) peak is more than 250 times stronger than the (220) and (311) peaks (note that the intensity is plotted in log scale). This observation means that most {111} planes are parallel to the surface of the GeSn thin film as well as the GeSn/SiO2 interface. In diamond cubic structures, {111} planes are the closest packed crystal planes, and thus have the lowest surface/interface free energy [29]. Therefore, the strong (111) texture is likely due to the tendency to minimize surface/interface free energy. Secondly, after annealing the sample with 9.5 at.% Sn shows a much better crystallinity than the pure Ge sample, as evidenced by the much stronger and narrower (111) peak, even though its annealing temperature is ~200 °C lower. The high crystallinity of the GeSn sample is also confirmed by the Raman spectra in Fig. 2(b). The full width at half maximum (FWHM) of the Ge-Ge peak for the crystallized 9.5 at.% Sn sample is 15 cm−1, approaching that of a single crystal Ge reference sample (10 cm−1). In Fig. 2(c), both the crystallization temperature and the intensity ratio of the strongest (111) peak to the second strongest peak (either (220) or (311)) in XRD are shown as a function of the Sn composition. The linear fit shows that the crystallization temperature decreases by ~20 °C with 1 at.% increase in the Sn composition, confirming what we anticipate for eutectically enhanced crystallization in Section 2. The low crystallization temperatures of 340~464 °C enable both BEOL CMOS processing for 3D photonic integration on Si microchips and virtual substrate fabrication on glass for cost-effective tandem solar cells. We also find that the (111) texture is strongly enhanced when the Sn composition increases from 0 to 9.5 at.%, with the intensity ratio of the strongest (111) peak to the second strongest peak increasing drastically from 1.8 to 270. As the Sn composition further increases beyond 10 at.%, this intensity ratio starts to decrease. This phenomenon is likely due to the fact that too much segregated Sn interrupts the grain growth of GeSn, thereby prohibiting the formation of a strong texture.

Another significant finding from Fig. 2(a) is that, compared to pure Ge with a lattice constant of 5.658 Å, the (111) peak of GeSn is shifted to a lower angle by 0.31 o to 26.97 o, corresponding to a lattice constant of a = 5.726 Å in the direction perpendicular to the thin film. Shifts in (220) and (311) peaks yield the same results. If there were no strain in the GeSn thin film, this lattice constant would correspond to a substitutional Sn composition of 8.1 at. % [20]. In reality, ~0.3% thermally induced tensile strain is expected upon cooling from 460 °C to room temperature, considering that in this temperature range the linear expansion coefficients of GeSn with ~8 at.% Sn and the Si substrate are ~9 × 10−6 and ~3 × 10-6 oC−1 [30], respectively. Since tensile strain shifts the XRD peaks to higher angles, thereby counteracting the effect of Sn alloying, the derived 8.1 at. % Sn without considering tensile strain is actually an underestimate. Remarkably, even this conservative estimate of the substitutional Sn composition far exceeds the equilibrium solubility limit of Sn in Ge (~1 at.%) [19], and it is comparable to that of the GeSn thin films grown by molecular beam epitaxy (MBE) [21]. Although in principle 2θ-sin2ψ measurement of a large-angle diffraction peak in XRD can help to determine the strain in a polycrystalline thin film [31] and obtain a more accurate Sn composition, in our case the large-angle peaks are too weak to provide accurate results because of the strong (111) texture. Instead, we perform EDS analysis of the crystallized GeSn thin film after etching away all the Sn segregates (more details to follow in the discussion of Fig. 3), and the content of Sn incorporated into the Ge matrix is determined to be 8.7 at.%. This Sn composition is further confirmed by Raman spectroscopy, as shown in Fig. 2(b). The Ge-Ge Raman peak of the crystallized 9.5 at.% Sn sample is at ~293 cm−1, notably shifted from that of the reference pure Ge single crystal sample at ~301 cm−1. According to ref. 32, this amount of shift in Ge-Ge Raman peak corresponds to a substitutional Sn composition of ~9 at.% without considering strain, essentially consistent with our EDS results. The slight overestimate compared to EDS is most likely due to the existence of tensile strain, which shifts the Ge-Ge peak to the same direction as Sn alloying. This large substitutional Sn composition well beyond the solubility limit is most likely due to the fact that the crystallization starts with a non-equilibrium amorphous phase, rather than the equilibrium liquid phase as described by the phase diagram. We also characterize the samples crystallized from a-GeSn films with Sn compositions from 12.8 to 16.5 at.%, and all of them also have ~8-9 at.% Sn incorporated into the Ge lattice. Therefore, it seems that the solubility limit of Sn in Ge is increased to ~9 at.% when crystallization occurs from the non-equilibrium amorphous phase rather than the equilibrium liquid phase.

 

Fig. 3 (a) SEM image of the GeSn sample with 9.5 at.% Sn after annealing at 464°C for 30 minutes. The bright dots and lines are identified to be Sn segregates by EDS. (b) SEM image of the annealed 9.5 at.% Sn sample after etching away Sn segregates on the surface, leaving behind the highly textured Ge0.913Sn0.087 thin film. (c) EBSD mapping of exactly the same region as shown in (b), where different colors indicate different in-plane crystallographic orientations. Grains that are ~5 μm wide and tens of microns long are observed. The average grain size is ~10 μm (d) EBSD mapping of the GeSn sample with 14.5 at.% Sn after annealing at 410 °C and etching away the Sn precipitates. While there are more small grains present, the average grain size is still ~5 μm.

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The 8.7 at. % Sn composition corresponds to an unstrained lattice constant of 5.731 Å [20]. Compared to a = 5.726 Å measured by XRD, the strain perpendicular to the GeSn thin film is determined to be ε = −0.09%. Since the Ge composition is still >90 at.%, if we further assume that Ge0.913Sn0.087 has the same Poisson ratio as pure Ge, which is 0.37 for (111) oriented films under biaxial tensile stress [33], then the in-plane tensile strain in the GeSn thin film is estimated to be 0.24%. This result is consistent with the ~0.3% tensile strain estimated earlier from the difference in thermal expansion coefficients between GeSn and Si, and it further helps to enhance the optoelectronic properties [28]. Accordingly, the in-plane lattice constant is a||≈5.74 Å. This lattice constant is only 0.17% mismatched to those of In0.65Ga0.35P and In0.17Ga0.83As (a = 5.73 Å), two ternary semiconductors optimized for triple junction tandem solar cells [11,22]. By comparison, the lattice mismatch between these ternary semiconductors and conventional Ge or GaAs substrates is as large as 1.1%, which requires sophisticated buffer layers to accommodate the misfit dislocations. Therefore, this highly textured GeSn layer could potentially serve as a seed layer to grow high-performance tandem solar cells on inexpensive amorphous substrates such as glass.

Considering that the Sn composition in the GeSn thin film is decreased from 9.5 at.% to 8.7 at.% after crystallization, we determine that ~0.8 at.% Sn is phase-separated from the highly (111) textured Ge0.913Sn0.087 film, contributing to the β-Sn peaks in Fig. 2(a). This result is consistent with our expectation for the eutectic-mediated crystallization process, where the Sn-rich liquid phase is segregated upon crystallization of the Ge-rich GeSn solid phase. Figure 3(a) further shows the plane-view SEM image of the 9.5 at.% Sn sample after annealing. The white dendritic lines are confirmed to be highly rich in Sn by EDS and back-scattered electron mode in SEM, a result of the Sn-rich liquid phase segregation.

This dendritic pattern of segregated Sn somewhat resembles the feature of phase segregation along the grain boundaries. To confirm the assumption that Sn segregates exclusively at the GeSn grain boundaries, we use 37.2% HCl:H2O solution with a high Sn-to-GeSn (Ge-rich) etching selectivity >4800:1 to selectively remove the Sn segregates without attacking the GeSn thin film. Figure 3(b) shows the surface view of the annealed 9.5 at.% Sn sample after etching away the Sn segregates, leaving the highly textured Ge0.913Sn0.087 thin film intact. The grooves correspond to the positions formerly occupied by the dendritic lines of Sn segregates. This profile is similar to typical grain boundaries exposed by selective etching [34]. Figure 3(c) shows an EBSD mapping of exactly the same area as in Fig. 3(b). Different colors in Fig. 3(c) correspond to different crystallographic orientations and therefore, different grains. Consistent with our assumption, the dendritic feature is resembled in the EBSD mapping, indicating that the grooves indeed correspond to the grain boundaries in the Ge0.913Sn0.087 thin film. The EBSD mapping in Fig. 3(c) also reveals additional boundaries that do not directly correspond to the etching grooves in Fig. 3(b). They turn out to be twin boundaries that do not have dangling bonds to accommodate Sn segregates. Remarkably, from the analyses in Figs. 3(b) and 3(c), we demonstrate that the highly (111) textured Ge0.913Sn0.087 thin film consists of large grains that are ~5 μm wide and tens of microns long. The average grain size is ~10 μm. When increasing the Sn composition in the as-deposited film to 14.5 at.%, the EBSD mapping in Fig. 3(d) shows that, although more small grains are present, an average grain size of ~5 μm is still obtained after crystallization annealing at 410 °C. These results again confirm the effectiveness of eutectically enhanced crystallization in the Ge-Sn system.

Furthermore, in Fig. 4(a) we show the distribution of misorientation angles between neighboring grains derived from the EBSD data of the highly textured Ge0.913Sn0.087 thin film in Fig. 3(c). Most of the misorientations are close to 60 o, which indicates Σ3 twin boundaries. Besides, there is a considerable amount of low-angle boundaries below 10 o. Twin boundaries are benign to the optoelectronic properties since no dangling bonds are introduced to form recombination centers. It has also been shown [35] that polycrystalline thin films with low-angle grain boundaries have significantly enhanced carrier mobility due to the reduced densities of defect recombination/scattering centers compared to those with random in-plane grain orientations. This also benefits the performance of electronic and optoelectronic devices. The inverse pole figure shown in the inset of Fig. 4(a), obtained by EBSD mapping over a large area of 0.2 × 0.2 mm2, confirms the strong (111) texture of the Ge0.913Sn0.087 thin film from the XRD results. Therefore, this high crystallinity Ge0.913Sn0.087 thin film on SiO2, obtained by crystallizing the 9.5 at.% Sn sample, is a significant step towards growing low defect density, near single crystalline GeSn on amorphous materials.

 

Fig. 4 (a) Distribution of misorientation angles between neighboring grains derived from the EBSD data of the highly textured Ge0.913Sn0.087 thin film in Fig. 3(c). The sample is crystallized from the a-GeSn thin film with 9.5 at.% Sn. The inset shows the inverse pole figure obtained over a 0.2 × 0.2 mm2 area, confirming the strong (111) texture. (b) Distribution of misorientation angles between neighboring grains for the 14.5 at.% Sn sample after crystallization annealing and etching away the Sn segregates. The inset shows the inverse pole figure obtained from the same EBSD mapping.

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Corresponding to Fig. 3(d), Fig. 4(b) shows the distribution of misorientation angles between neighboring grains for the 14.5 at. % Sn sample after crystallization at 410 °C. Although the Σ3 twin boundaries are still dominant, we start to see high-angle boundaries with a misorientation of ~37 o. These are the well-known Σ5 grain boundaries [35]. The presence of small grains in Fig. 3(d) and high-angle grain boundaries in Fig. 4(b) both indicate that too much Sn segregation interrupts the growth of GeSn grains. The inverse pole figure in the inset of Fig. 4(b) is consistent with the XRD results presented earlier, showing a weaker (111) texture as the Sn composition increases beyond 10 at.%.

To elucidate the formation mechanism of large grains and twin/low-angle grain boundaries in the GeSn thin films, Figs. 5(a) and 5(b) show large-area SEM surface images of the high crystallinity Ge0.913Sn0.087 thin film previously shown in Figs. 3(b) and 3(c). In an area as large as 1.6 mm2 in Fig. 5(a), we only observe 6 nucleation centers as indicated by the numbers and arrows on the graph, from which the GeSn grains grow radially (see Fig. 5(b)). The spacing between the nucleation centers is 0.1~1 mm, orders of magnitude larger than that of regular solid phase crystallization in semiconductor thin films. This striking observation suggests an extraordinarily fast lateral grain growth rate vs. a slow nucleation rate during the eutectically enhanced crystallization process of GeSn. In fact, even when we reduce the annealing time from 30 minutes of tube furnace annealing to only 90 seconds of RTA, the resulting crystallinity and grain misorientation distributions are similar. This result confirms that the crystallization is indeed completed in a very short time, consistent with the exceedingly high lateral grain growth rate suggested above. The fast growth rate is highly beneficial in fabricating large-grained and near single crystalline GeSn on amorphous materials at a high throughput. The formation of twin boundaries and low-angle grain boundaries in a given growth domain of Fig. 5(a) is likely due to the perturbation of Sn segregation during the lateral growth process of GeSn grains from the same nucleation center.

 

Fig. 5 (a) Large-area SEM image of the highly textured Ge0.913Sn0.087 thin film previously shown in Figs. 3(b) and 3(c). The sample is crystallized from a-GeSn with 9.5 at.% Sn. The arrows point to 6 nucleation centers in an total area of ~1.6 mm2, from which GeSn grains grow radially. (b) A zoomed-in image of domain 2 in (a). (c) Large-area SEM image of the 14.5 at.% Sn sample after crystallization annealing and etching away Sn segregates. The radiating dendritic feature is still present, but the density of nucleation centers is increased compared to the 9.5 at. % Sn sample shown in (a) and (b). (d) Large-area SEM image of the 16.5 at.% Sn sample after crystallization annealing and etching away Sn segregates. The radiating dendritic feature is no longer present.

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Figures 5(c) and 5(d) further show the SEM images of the 14.5 and 16.5 at.% Sn samples after crystallization annealing and etching away Sn segregates, respectively. Clearly, as the starting Sn composition further increases beyond 10 at.%, the density of nucleation centers increases and grain growth becomes less dominant compared to nucleation. As a result, the average grain size decreases. In fact, the 16.5 at.% Sn sample no longer shows a radiating dendritic feature. From EBSD mapping (not shown), the average grain size is reduced to ~1 μm, and the fraction of large angle grain boundaries increases significantly. Therefore, the optimal Sn composition in the as-deposited a-GeSn thin film is ~10 at.% to achieve the best crystallinity after annealing.

As mentioned in Section 2, the incorporation of Sn into Ge also reduces the direct band gap and leads to a transformation from indirect to direct band gap material. To verify this point, Fig. 6(a) shows the transmittance spectrum of the highly (111) textured, large-grained Ge0.913Sn0.087 thin film mentioned earlier. Also shown for comparison is the transmittance spectrum of a reference sample without the GeSn thin film. Since the GeSn film is very thin (302 nm), the indirect gap absorption in the order of 10~100 cm−1 [36] could only lead to <0.3% decrease in transmittance. Therefore, the drastic decrease in transmittance at λ<2500 nm (hv>0.5 eV) for the Ge0.913Sn0.087 thin film has to be attributed to the efficient direct gap absorption in the order of 103-104 cm−1 [36]. Figure 6(b) shows the absorption coefficient data calculated from the transmittance measurement using transfer matrix method and Kramer-Kronig relation [37]. The order of magnitude of the absorption coefficients is indeed consistent with direct band gap absorption. The direct band gap of Ge0.913Sn0.087 is around 0.5 eV, significantly red-shifted from that of pure Ge (0.8 eV). This amount of red-shift is consistent with the result obtained from the epitaxial GeSn on Si with ~9 at.% Sn, approaching the indirect-to-direct gap transition [20,21] that greatly enhances absorption and emission efficiency for optoelectronic applications [17,18].

 

Fig. 6 (a) Transmittance spectrum of the high crystallinity Ge0.913Sn0.087 thin film sample compared to a reference sample without the GeSn thin film. (b) Absorption spectrum of Ge0.913Sn0.087 derived from the transmittance spectrum in (a).

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5. Conclusions

This work demonstrates that, by incorporating Sn into Ge to enhance crystallization through the Ge-Sn eutectic system and modify the band structure towards a direct gap semiconductor, we simultaneously achieve high crystallinity and significantly improved optoelectronic properties for GeSn thin films on amorphous SiO2 at low crystallization temperatures of 370~470 °C. The enhanced optoelectronic properties and low crystallization temperatures of GeSn represent a major step towards both BEOL CMOS processing for 3D photonic integration on Si microchips and virtual substrate fabrication on glass for cost-effective tandem solar cell. We find that the crystallization temperature decreases with the increase of Sn composition in the as-deposited a-GeSn thin films. The optimal crystallinity comes from the sample with 9.5 at.% Sn annealed at 464 °C, where a highly (111) textured Ge0.913Sn0.087 thin film with grain sizes up to tens of microns was crystallized on SiO2. The intensity ratio of the strongest (111) peak to the second strongest (311) peak in XRD is as high as 270 in this sample. Remarkably, the majority of the grain boundaries are either twin boundaries or low-angle boundaries, which is a significant step towards growing low defect density, near single crystalline GeSn on amorphous materials for optoelectronic and electronic devices. We also find that the large grains and the dominance of twin/low-angle grain boundaries are due to an extraordinarily large spacing of 0.1~1 mm between nucleation centers from which GeSn grains grow radially, indicating an exceedingly high lateral growth rate vs. a low nucleation rate in the eutectically enhanced crystallization process of GeSn. The fast grain growth offers high throughput for large area device fabrication.

Another significant finding is that up to 8.7 at.% Sn is incorporated substitutionally into the Ge lattice during the crystallization process, far exceeding the equilibrium solubility limit of ~1 at.%. As a result, the direct band gap red-shifts significantly from 0.8 eV for pure Ge to 0.5 eV for Ge0.913Sn0.087, approaching the indirect-to-direct gap transition that enhances the optoelectronic properties substantially. Furthermore, compared to Ge and GaAs, Ge0.913Sn0.087 is significantly better lattice-matched to In0.65Ga0.35P and In0.17Ga0.83As, two ternary semiconductors optimized for triple junction tandem cells. These results indicate that the high crystallinity GeSn thin film fabricated on amorphous layers at temperature <500 °C is a promising precursor towards near single crystalline GeSn materials and devices on dielectric layers or glass substrates for applications in both monolithic 3D photonic integration on Si and cost-effective tandem solar cells on GeSn/glass virtual substrates. The eutectically enhanced crystallization method demonstrated in this work can be extended to other eutectic systems for a broader range of applications.

Acknowledgments

We would like to thank Dr. Charles Daghlian and Prof. Christopher Levey for helpful discussions. This work is supported by the National Science Foundation under the grant number DMR-1255066.

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3. J. F. Liu, M. Beals, A. Pomerene, S. Bernardis, R. Sun, J. Cheng, L. C. Kimerling, and J. Michel, “Waveguide-integrated, ultra-low energy GeSi electro-absorption modulators,” Nat. Photonics 2(7), 433–437 (2008). [CrossRef]  

4. D. H. Ahn, C. Y. Hong, J. F. Liu, W. Giziewicz, M. Beals, L. C. Kimerling, J. Michel, J. Chen, and F. X. Kärtner, “High performance, waveguide integrated Ge photodetectors,” Opt. Express 15(7), 3916–3921 (2007). [CrossRef]   [PubMed]  

5. M. Beals, J. Michel, J. F. Liu, D. H. Ahn, D. Sparacin, R. Sun, C. Y. Hong, L. C. Kimerling, A. Pomerene, D. Carathers, J. Beattie, A. Kopa, and A. Apsel, “Process flow innovations for photonic device integration in CMOS,” Proc. SPIE 6898, 689804 (2008). [CrossRef]  

6. J. F. Liu, X. C. Sun, R. Camacho-Aguilera, L. C. Kimerling, and J. Michel, “Ge-on-Si laser operating at room temperature,” Opt. Lett. 35(5), 679–681 (2010). [CrossRef]   [PubMed]  

7. J. M. Fedeli, M. Migette, L. Di Cioccio, L. El Melhaoui, R. Orobtchouk, C. Seassal, P. Rojoromeo, F. Mandorlo, D. Marris Morini, and L. Vivien, “Incorporation of a photonic layer at the metallization levels of a CMOS circuit,” in Proceedings of IEEE International Conference on Group IV Photonics (Institute of Electrical and Electronics Engineers, 2006), pp. 200–202.

8. P. Koonath and B. Jalali, “Multilayer 3-D photonics in silicon,” Opt. Express 15(20), 12686–12691 (2007). [CrossRef]   [PubMed]  

9. B. Guha, B. B. C. Kyotoku, and M. Lipson, “CMOS-compatible athermal silicon microring resonators,” Opt. Express 18(4), 3487–3493 (2010). [CrossRef]   [PubMed]  

10. K. Wada, “Challenges of Si Photonics for on-chip Integration,” in Proceedings of European Conference of Optical Communication (ECOC), (Vienna, Austria, September, 2009), paper 2.7.3.

11. F. Dimroth and S. Kurtz, “High-efficiency multijunction solar cells,” MRS Bull. 32(03), 230–235 (2007). [CrossRef]  

12. H. Kanno, K. Atsushi, T. Sadoh, and M. Miyao, “Ge-enhanced MILC velocity in a-Ge/a-Si/SiO2layered structure,” Mater. Sci. Semicond. Process. 8(1-3), 83–88 (2005). [CrossRef]  

13. C. H. Yu, P. H. Yeh, S. L. Cheng, L. J. Chen, and L. W. Cheng, “Metal-induced crystallization of amorphous Si1-xGex by rapid thermal annealing,” Thin Solid Films 469–470, 356–360 (2004). [CrossRef]  

14. C. M. Yang and H. A. Atwater, “Selective solid phase crystallization for control of grain size and location in Ge thin films on silicon dioxide,” Appl. Phys. Lett. 68(24), 3392–3394 (1996). [CrossRef]  

15. K. McComber, X. Duan, J. F. Liu, J. Michel, and L. C. Kimerling, “Single-crystal germanium growth on amorphous silicon,” Adv. Funct. Mater. 22(5), 1048–1057 (2012). [CrossRef]  

16. S. Gupta, B. Vincent, B. Yang, D. Lin, F. Gencarelli, J.-Y. J. Lin, R. Chen, O. Richard, H. Bender, B. Magyari-Köpe, M. Caymax, J. Dekoster, Y. Nishi, and K. C. Saraswat, “Towards high mobility GeSn channel nMOSFETs: Improved surface passivation using novel ozone oxidation method,” in Proceedings of IEEE Electronic Device Meeting (Institute of Electrical and Electronics Engineers, San Francisco, 2012), pp. 16.2.1–16.2.4. [CrossRef]  

17. J. Werner, M. Oehme, M. Schmid, M. Kaschel, A. Schirmer, E. Kasper, and J. Schulze, “Germanium-tin p-i-n photodetectors integrated on silicon grown by molecular beam epitaxy,” Appl. Phys. Lett. 98(6), 061108 (2011). [CrossRef]  

18. R. Roucka, J. Mathews, R. T. Beeler, J. Tolle, J. Kouvetakis, and J. Menéndez, “Direct gap electroluminescence from Si/Ge1-ySny p-i-n heterostructure diodes,” Appl. Phys. Lett. 98(6), 061109 (2011). [CrossRef]  

19. B. Predel, “Ge-Sn binary phase diagram,” in Landolt-Börnstein Database: Group IV Physical Chemistry, Numerical Data and Functional Relationship in Science and Technology. O. Madelung ed. New Series IV/5, vol. 5f (Springer, 2013). http://www.springermaterials.com/docs/info/10501684_1506.html.

20. V. R. D’Costa, C. S. Cook, A. G. Birdwell, C. L. Littler, M. Canonico, S. Zollner, J. Kouvetakis, and J. Menéndez, “Optical critical points of thin-film Ge1-ySny alloys: a comparative Ge1-ySny/Ge1-xSix study,” Phys. Rev. B 73(12), 125207 (2006). [CrossRef]  

21. R. Chen, H. Lin, Y. Huo, C. Hitzman, T. I. Kamins, and J. S. Harris, “Increased photoluminescence of strain-reduced, high-Sn composition Ge1−xSnx alloys grown by molecular beam epitaxy,” Appl. Phys. Lett. 99(18), 181125 (2011). [CrossRef]  

22. W. Guter, J. Schöne, S. P. Philipps, M. Steiner, G. Siefer, A. Wekkeli, E. Welser, E. Oliva, A. W. Bett, and F. Dimroth, “Current-matched triple-junction solar cell reaching 41.1% conversion efficiency under concentrated sunlight,” Appl. Phys. Lett. 94(22), 223504 (2009). [CrossRef]  

23. G. He and H. A. Atwater, “Interband transitions in SnxGe1-x alloys,” Phys. Rev. Lett. 79(10), 1937–1940 (1997). [CrossRef]  

24. H. Pérez Ladrón de Guevara, A. G. Rodríguez, H. Navarro-Contreras, and M. A. Vidal, “Ge1-xSnx alloys pseudomorphically grown on Ge(001),” Appl. Phys. Lett. 83(24), 4942–4944 (2003). [CrossRef]  

25. M. G. Mauk, Liquid Phase Epitaxy of Electronic, Optical, and Optoelectronic Materials (Wiley, 2007), Chap. 5.

26. A. S. Saidov, A. Sh. Razzakov, and É. A. Koshchanov, “Liquid phase epitaxy of Ge1-xSnx thin fims,” Tech. Phys. Lett. 27(8), 698–700 (2001). [CrossRef]  

27. R. A. Soref and L. Friedman, “Direct gap Ge/GeSn/Si and GeSn/Ge/Si heterostructures,” Superlattices Microstruct. 14(2-3), 189–193 (1993). [CrossRef]  

28. R. A. Soref, J. Kouvetakis, J. Tolle, J. Menendez, and V. D’Costa, “Advances in SiGeSn technology,” J. Mater. Res. 22(12), 3281–3291 (2007). [CrossRef]  

29. R. J. Jaccodine, “Surface Energy of Germanium and Silicon,” J. Electrochem. Soc. 110(6), 524–527 (1963). [CrossRef]  

30. R. Roucka, Y.-Y. Fang, J. Kouvetakis, A. V. G. Chizmeshya, and J. Menéndez, “Thermal expansivity of Ge1-ySny alloys,” Phys. Rev. B 81(24), 245214 (2010). [CrossRef]  

31. P. Water, Stress Analysis and Mechanical Characterization of Thin Films for Microelectronics and MEMS Applications (ProQuest, 2008), Chap. 3, pp. 78–95.

32. V. R. D’Costa, J. Tolle, R. Roucka, J. Kouvetakis, and J. Menendez, “Raman scattering in Ge1-ySny alloys,” Solid State Commun. 144(5-6), 240–244 (2007). [CrossRef]  

33. C. G. Van de Walle, “Band lineups and deformation potentials in the model-solid theory,” Phys. Rev. B Condens. Matter 39(3), 1871–1883 (1989). [CrossRef]   [PubMed]  

34. J. F. Shackelford, Introduction to Materials Science for Engineers, 5th Ed. (Prentice-Hall, 2000), Chap. 4.

35. W. Choi, A. T. Findikoglu, M. J. Romero, and M. Al-Jassim, “Effect of grain alignment on lateral carrier transport in aligned-crystalline silicon films on polycrystalline substrates,” J. Mater. Res. 22(04), 821–825 (2007). [CrossRef]  

36. A. Frova and P. Handler, “Franz-Keldysh effect in the space-charge region of a germanium p-n junction,” Phys. Rev. 137(6A), A1857–A1862 (1965). [CrossRef]  

37. J. F. Liu, X. Sun, L. C. Kimerling, and J. Michel, “Direct-gap optical gain of Ge on Si at room temperature,” Opt. Lett. 34(11), 1738–1740 (2009). [CrossRef]   [PubMed]  

References

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  • |

  1. R. Kirchain and L. C. Kimerling, “A roadmap for nanophotonics,” Nat. Photonics 1(6), 303–305 (2007).
    [Crossref]
  2. R. A. Soref, “The past, present, and future of silicon photonics,” IEEE Sel. Top. Quantum. Electron. 12(6), 1678–1687 (2006).
    [Crossref]
  3. J. F. Liu, M. Beals, A. Pomerene, S. Bernardis, R. Sun, J. Cheng, L. C. Kimerling, and J. Michel, “Waveguide-integrated, ultra-low energy GeSi electro-absorption modulators,” Nat. Photonics 2(7), 433–437 (2008).
    [Crossref]
  4. D. H. Ahn, C. Y. Hong, J. F. Liu, W. Giziewicz, M. Beals, L. C. Kimerling, J. Michel, J. Chen, and F. X. Kärtner, “High performance, waveguide integrated Ge photodetectors,” Opt. Express 15(7), 3916–3921 (2007).
    [Crossref] [PubMed]
  5. M. Beals, J. Michel, J. F. Liu, D. H. Ahn, D. Sparacin, R. Sun, C. Y. Hong, L. C. Kimerling, A. Pomerene, D. Carathers, J. Beattie, A. Kopa, and A. Apsel, “Process flow innovations for photonic device integration in CMOS,” Proc. SPIE 6898, 689804 (2008).
    [Crossref]
  6. J. F. Liu, X. C. Sun, R. Camacho-Aguilera, L. C. Kimerling, and J. Michel, “Ge-on-Si laser operating at room temperature,” Opt. Lett. 35(5), 679–681 (2010).
    [Crossref] [PubMed]
  7. J. M. Fedeli, M. Migette, L. Di Cioccio, L. El Melhaoui, R. Orobtchouk, C. Seassal, P. Rojoromeo, F. Mandorlo, D. Marris Morini, and L. Vivien, “Incorporation of a photonic layer at the metallization levels of a CMOS circuit,” in Proceedings of IEEE International Conference on Group IV Photonics (Institute of Electrical and Electronics Engineers, 2006), pp. 200–202.
  8. P. Koonath and B. Jalali, “Multilayer 3-D photonics in silicon,” Opt. Express 15(20), 12686–12691 (2007).
    [Crossref] [PubMed]
  9. B. Guha, B. B. C. Kyotoku, and M. Lipson, “CMOS-compatible athermal silicon microring resonators,” Opt. Express 18(4), 3487–3493 (2010).
    [Crossref] [PubMed]
  10. K. Wada, “Challenges of Si Photonics for on-chip Integration,” in Proceedings of European Conference of Optical Communication (ECOC), (Vienna, Austria, September, 2009), paper 2.7.3.
  11. F. Dimroth and S. Kurtz, “High-efficiency multijunction solar cells,” MRS Bull. 32(03), 230–235 (2007).
    [Crossref]
  12. H. Kanno, K. Atsushi, T. Sadoh, and M. Miyao, “Ge-enhanced MILC velocity in a-Ge/a-Si/SiO2layered structure,” Mater. Sci. Semicond. Process. 8(1-3), 83–88 (2005).
    [Crossref]
  13. C. H. Yu, P. H. Yeh, S. L. Cheng, L. J. Chen, and L. W. Cheng, “Metal-induced crystallization of amorphous Si1-xGex by rapid thermal annealing,” Thin Solid Films 469–470, 356–360 (2004).
    [Crossref]
  14. C. M. Yang and H. A. Atwater, “Selective solid phase crystallization for control of grain size and location in Ge thin films on silicon dioxide,” Appl. Phys. Lett. 68(24), 3392–3394 (1996).
    [Crossref]
  15. K. McComber, X. Duan, J. F. Liu, J. Michel, and L. C. Kimerling, “Single-crystal germanium growth on amorphous silicon,” Adv. Funct. Mater. 22(5), 1048–1057 (2012).
    [Crossref]
  16. S. Gupta, B. Vincent, B. Yang, D. Lin, F. Gencarelli, J.-Y. J. Lin, R. Chen, O. Richard, H. Bender, B. Magyari-Köpe, M. Caymax, J. Dekoster, Y. Nishi, and K. C. Saraswat, “Towards high mobility GeSn channel nMOSFETs: Improved surface passivation using novel ozone oxidation method,” in Proceedings of IEEE Electronic Device Meeting (Institute of Electrical and Electronics Engineers, San Francisco, 2012), pp. 16.2.1–16.2.4.
    [Crossref]
  17. J. Werner, M. Oehme, M. Schmid, M. Kaschel, A. Schirmer, E. Kasper, and J. Schulze, “Germanium-tin p-i-n photodetectors integrated on silicon grown by molecular beam epitaxy,” Appl. Phys. Lett. 98(6), 061108 (2011).
    [Crossref]
  18. R. Roucka, J. Mathews, R. T. Beeler, J. Tolle, J. Kouvetakis, and J. Menéndez, “Direct gap electroluminescence from Si/Ge1-ySny p-i-n heterostructure diodes,” Appl. Phys. Lett. 98(6), 061109 (2011).
    [Crossref]
  19. B. Predel, “Ge-Sn binary phase diagram,” in Landolt-Börnstein Database: Group IV Physical Chemistry, Numerical Data and Functional Relationship in Science and Technology. O. Madelung ed. New Series IV/5, vol. 5f (Springer, 2013). http://www.springermaterials.com/docs/info/10501684_1506.html .
  20. V. R. D’Costa, C. S. Cook, A. G. Birdwell, C. L. Littler, M. Canonico, S. Zollner, J. Kouvetakis, and J. Menéndez, “Optical critical points of thin-film Ge1-ySny alloys: a comparative Ge1-ySny/Ge1-xSix study,” Phys. Rev. B 73(12), 125207 (2006).
    [Crossref]
  21. R. Chen, H. Lin, Y. Huo, C. Hitzman, T. I. Kamins, and J. S. Harris, “Increased photoluminescence of strain-reduced, high-Sn composition Ge1−xSnx alloys grown by molecular beam epitaxy,” Appl. Phys. Lett. 99(18), 181125 (2011).
    [Crossref]
  22. W. Guter, J. Schöne, S. P. Philipps, M. Steiner, G. Siefer, A. Wekkeli, E. Welser, E. Oliva, A. W. Bett, and F. Dimroth, “Current-matched triple-junction solar cell reaching 41.1% conversion efficiency under concentrated sunlight,” Appl. Phys. Lett. 94(22), 223504 (2009).
    [Crossref]
  23. G. He and H. A. Atwater, “Interband transitions in SnxGe1-x alloys,” Phys. Rev. Lett. 79(10), 1937–1940 (1997).
    [Crossref]
  24. H. Pérez Ladrón de Guevara, A. G. Rodríguez, H. Navarro-Contreras, and M. A. Vidal, “Ge1-xSnx alloys pseudomorphically grown on Ge(001),” Appl. Phys. Lett. 83(24), 4942–4944 (2003).
    [Crossref]
  25. M. G. Mauk, Liquid Phase Epitaxy of Electronic, Optical, and Optoelectronic Materials (Wiley, 2007), Chap. 5.
  26. A. S. Saidov, A. Sh. Razzakov, and É. A. Koshchanov, “Liquid phase epitaxy of Ge1-xSnx thin fims,” Tech. Phys. Lett. 27(8), 698–700 (2001).
    [Crossref]
  27. R. A. Soref and L. Friedman, “Direct gap Ge/GeSn/Si and GeSn/Ge/Si heterostructures,” Superlattices Microstruct. 14(2-3), 189–193 (1993).
    [Crossref]
  28. R. A. Soref, J. Kouvetakis, J. Tolle, J. Menendez, and V. D’Costa, “Advances in SiGeSn technology,” J. Mater. Res. 22(12), 3281–3291 (2007).
    [Crossref]
  29. R. J. Jaccodine, “Surface Energy of Germanium and Silicon,” J. Electrochem. Soc. 110(6), 524–527 (1963).
    [Crossref]
  30. R. Roucka, Y.-Y. Fang, J. Kouvetakis, A. V. G. Chizmeshya, and J. Menéndez, “Thermal expansivity of Ge1-ySny alloys,” Phys. Rev. B 81(24), 245214 (2010).
    [Crossref]
  31. P. Water, Stress Analysis and Mechanical Characterization of Thin Films for Microelectronics and MEMS Applications (ProQuest, 2008), Chap. 3, pp. 78–95.
  32. V. R. D’Costa, J. Tolle, R. Roucka, J. Kouvetakis, and J. Menendez, “Raman scattering in Ge1-ySny alloys,” Solid State Commun. 144(5-6), 240–244 (2007).
    [Crossref]
  33. C. G. Van de Walle, “Band lineups and deformation potentials in the model-solid theory,” Phys. Rev. B Condens. Matter 39(3), 1871–1883 (1989).
    [Crossref] [PubMed]
  34. J. F. Shackelford, Introduction to Materials Science for Engineers, 5th Ed. (Prentice-Hall, 2000), Chap. 4.
  35. W. Choi, A. T. Findikoglu, M. J. Romero, and M. Al-Jassim, “Effect of grain alignment on lateral carrier transport in aligned-crystalline silicon films on polycrystalline substrates,” J. Mater. Res. 22(04), 821–825 (2007).
    [Crossref]
  36. A. Frova and P. Handler, “Franz-Keldysh effect in the space-charge region of a germanium p-n junction,” Phys. Rev. 137(6A), A1857–A1862 (1965).
    [Crossref]
  37. J. F. Liu, X. Sun, L. C. Kimerling, and J. Michel, “Direct-gap optical gain of Ge on Si at room temperature,” Opt. Lett. 34(11), 1738–1740 (2009).
    [Crossref] [PubMed]

2012 (1)

K. McComber, X. Duan, J. F. Liu, J. Michel, and L. C. Kimerling, “Single-crystal germanium growth on amorphous silicon,” Adv. Funct. Mater. 22(5), 1048–1057 (2012).
[Crossref]

2011 (3)

J. Werner, M. Oehme, M. Schmid, M. Kaschel, A. Schirmer, E. Kasper, and J. Schulze, “Germanium-tin p-i-n photodetectors integrated on silicon grown by molecular beam epitaxy,” Appl. Phys. Lett. 98(6), 061108 (2011).
[Crossref]

R. Roucka, J. Mathews, R. T. Beeler, J. Tolle, J. Kouvetakis, and J. Menéndez, “Direct gap electroluminescence from Si/Ge1-ySny p-i-n heterostructure diodes,” Appl. Phys. Lett. 98(6), 061109 (2011).
[Crossref]

R. Chen, H. Lin, Y. Huo, C. Hitzman, T. I. Kamins, and J. S. Harris, “Increased photoluminescence of strain-reduced, high-Sn composition Ge1−xSnx alloys grown by molecular beam epitaxy,” Appl. Phys. Lett. 99(18), 181125 (2011).
[Crossref]

2010 (3)

2009 (2)

J. F. Liu, X. Sun, L. C. Kimerling, and J. Michel, “Direct-gap optical gain of Ge on Si at room temperature,” Opt. Lett. 34(11), 1738–1740 (2009).
[Crossref] [PubMed]

W. Guter, J. Schöne, S. P. Philipps, M. Steiner, G. Siefer, A. Wekkeli, E. Welser, E. Oliva, A. W. Bett, and F. Dimroth, “Current-matched triple-junction solar cell reaching 41.1% conversion efficiency under concentrated sunlight,” Appl. Phys. Lett. 94(22), 223504 (2009).
[Crossref]

2008 (2)

J. F. Liu, M. Beals, A. Pomerene, S. Bernardis, R. Sun, J. Cheng, L. C. Kimerling, and J. Michel, “Waveguide-integrated, ultra-low energy GeSi electro-absorption modulators,” Nat. Photonics 2(7), 433–437 (2008).
[Crossref]

M. Beals, J. Michel, J. F. Liu, D. H. Ahn, D. Sparacin, R. Sun, C. Y. Hong, L. C. Kimerling, A. Pomerene, D. Carathers, J. Beattie, A. Kopa, and A. Apsel, “Process flow innovations for photonic device integration in CMOS,” Proc. SPIE 6898, 689804 (2008).
[Crossref]

2007 (7)

V. R. D’Costa, J. Tolle, R. Roucka, J. Kouvetakis, and J. Menendez, “Raman scattering in Ge1-ySny alloys,” Solid State Commun. 144(5-6), 240–244 (2007).
[Crossref]

W. Choi, A. T. Findikoglu, M. J. Romero, and M. Al-Jassim, “Effect of grain alignment on lateral carrier transport in aligned-crystalline silicon films on polycrystalline substrates,” J. Mater. Res. 22(04), 821–825 (2007).
[Crossref]

R. A. Soref, J. Kouvetakis, J. Tolle, J. Menendez, and V. D’Costa, “Advances in SiGeSn technology,” J. Mater. Res. 22(12), 3281–3291 (2007).
[Crossref]

D. H. Ahn, C. Y. Hong, J. F. Liu, W. Giziewicz, M. Beals, L. C. Kimerling, J. Michel, J. Chen, and F. X. Kärtner, “High performance, waveguide integrated Ge photodetectors,” Opt. Express 15(7), 3916–3921 (2007).
[Crossref] [PubMed]

R. Kirchain and L. C. Kimerling, “A roadmap for nanophotonics,” Nat. Photonics 1(6), 303–305 (2007).
[Crossref]

F. Dimroth and S. Kurtz, “High-efficiency multijunction solar cells,” MRS Bull. 32(03), 230–235 (2007).
[Crossref]

P. Koonath and B. Jalali, “Multilayer 3-D photonics in silicon,” Opt. Express 15(20), 12686–12691 (2007).
[Crossref] [PubMed]

2006 (2)

V. R. D’Costa, C. S. Cook, A. G. Birdwell, C. L. Littler, M. Canonico, S. Zollner, J. Kouvetakis, and J. Menéndez, “Optical critical points of thin-film Ge1-ySny alloys: a comparative Ge1-ySny/Ge1-xSix study,” Phys. Rev. B 73(12), 125207 (2006).
[Crossref]

R. A. Soref, “The past, present, and future of silicon photonics,” IEEE Sel. Top. Quantum. Electron. 12(6), 1678–1687 (2006).
[Crossref]

2005 (1)

H. Kanno, K. Atsushi, T. Sadoh, and M. Miyao, “Ge-enhanced MILC velocity in a-Ge/a-Si/SiO2layered structure,” Mater. Sci. Semicond. Process. 8(1-3), 83–88 (2005).
[Crossref]

2004 (1)

C. H. Yu, P. H. Yeh, S. L. Cheng, L. J. Chen, and L. W. Cheng, “Metal-induced crystallization of amorphous Si1-xGex by rapid thermal annealing,” Thin Solid Films 469–470, 356–360 (2004).
[Crossref]

2003 (1)

H. Pérez Ladrón de Guevara, A. G. Rodríguez, H. Navarro-Contreras, and M. A. Vidal, “Ge1-xSnx alloys pseudomorphically grown on Ge(001),” Appl. Phys. Lett. 83(24), 4942–4944 (2003).
[Crossref]

2001 (1)

A. S. Saidov, A. Sh. Razzakov, and É. A. Koshchanov, “Liquid phase epitaxy of Ge1-xSnx thin fims,” Tech. Phys. Lett. 27(8), 698–700 (2001).
[Crossref]

1997 (1)

G. He and H. A. Atwater, “Interband transitions in SnxGe1-x alloys,” Phys. Rev. Lett. 79(10), 1937–1940 (1997).
[Crossref]

1996 (1)

C. M. Yang and H. A. Atwater, “Selective solid phase crystallization for control of grain size and location in Ge thin films on silicon dioxide,” Appl. Phys. Lett. 68(24), 3392–3394 (1996).
[Crossref]

1993 (1)

R. A. Soref and L. Friedman, “Direct gap Ge/GeSn/Si and GeSn/Ge/Si heterostructures,” Superlattices Microstruct. 14(2-3), 189–193 (1993).
[Crossref]

1989 (1)

C. G. Van de Walle, “Band lineups and deformation potentials in the model-solid theory,” Phys. Rev. B Condens. Matter 39(3), 1871–1883 (1989).
[Crossref] [PubMed]

1965 (1)

A. Frova and P. Handler, “Franz-Keldysh effect in the space-charge region of a germanium p-n junction,” Phys. Rev. 137(6A), A1857–A1862 (1965).
[Crossref]

1963 (1)

R. J. Jaccodine, “Surface Energy of Germanium and Silicon,” J. Electrochem. Soc. 110(6), 524–527 (1963).
[Crossref]

Ahn, D. H.

M. Beals, J. Michel, J. F. Liu, D. H. Ahn, D. Sparacin, R. Sun, C. Y. Hong, L. C. Kimerling, A. Pomerene, D. Carathers, J. Beattie, A. Kopa, and A. Apsel, “Process flow innovations for photonic device integration in CMOS,” Proc. SPIE 6898, 689804 (2008).
[Crossref]

D. H. Ahn, C. Y. Hong, J. F. Liu, W. Giziewicz, M. Beals, L. C. Kimerling, J. Michel, J. Chen, and F. X. Kärtner, “High performance, waveguide integrated Ge photodetectors,” Opt. Express 15(7), 3916–3921 (2007).
[Crossref] [PubMed]

Al-Jassim, M.

W. Choi, A. T. Findikoglu, M. J. Romero, and M. Al-Jassim, “Effect of grain alignment on lateral carrier transport in aligned-crystalline silicon films on polycrystalline substrates,” J. Mater. Res. 22(04), 821–825 (2007).
[Crossref]

Apsel, A.

M. Beals, J. Michel, J. F. Liu, D. H. Ahn, D. Sparacin, R. Sun, C. Y. Hong, L. C. Kimerling, A. Pomerene, D. Carathers, J. Beattie, A. Kopa, and A. Apsel, “Process flow innovations for photonic device integration in CMOS,” Proc. SPIE 6898, 689804 (2008).
[Crossref]

Atsushi, K.

H. Kanno, K. Atsushi, T. Sadoh, and M. Miyao, “Ge-enhanced MILC velocity in a-Ge/a-Si/SiO2layered structure,” Mater. Sci. Semicond. Process. 8(1-3), 83–88 (2005).
[Crossref]

Atwater, H. A.

G. He and H. A. Atwater, “Interband transitions in SnxGe1-x alloys,” Phys. Rev. Lett. 79(10), 1937–1940 (1997).
[Crossref]

C. M. Yang and H. A. Atwater, “Selective solid phase crystallization for control of grain size and location in Ge thin films on silicon dioxide,” Appl. Phys. Lett. 68(24), 3392–3394 (1996).
[Crossref]

Beals, M.

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J. F. Liu, M. Beals, A. Pomerene, S. Bernardis, R. Sun, J. Cheng, L. C. Kimerling, and J. Michel, “Waveguide-integrated, ultra-low energy GeSi electro-absorption modulators,” Nat. Photonics 2(7), 433–437 (2008).
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D. H. Ahn, C. Y. Hong, J. F. Liu, W. Giziewicz, M. Beals, L. C. Kimerling, J. Michel, J. Chen, and F. X. Kärtner, “High performance, waveguide integrated Ge photodetectors,” Opt. Express 15(7), 3916–3921 (2007).
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M. Beals, J. Michel, J. F. Liu, D. H. Ahn, D. Sparacin, R. Sun, C. Y. Hong, L. C. Kimerling, A. Pomerene, D. Carathers, J. Beattie, A. Kopa, and A. Apsel, “Process flow innovations for photonic device integration in CMOS,” Proc. SPIE 6898, 689804 (2008).
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J. F. Liu, M. Beals, A. Pomerene, S. Bernardis, R. Sun, J. Cheng, L. C. Kimerling, and J. Michel, “Waveguide-integrated, ultra-low energy GeSi electro-absorption modulators,” Nat. Photonics 2(7), 433–437 (2008).
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W. Guter, J. Schöne, S. P. Philipps, M. Steiner, G. Siefer, A. Wekkeli, E. Welser, E. Oliva, A. W. Bett, and F. Dimroth, “Current-matched triple-junction solar cell reaching 41.1% conversion efficiency under concentrated sunlight,” Appl. Phys. Lett. 94(22), 223504 (2009).
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V. R. D’Costa, C. S. Cook, A. G. Birdwell, C. L. Littler, M. Canonico, S. Zollner, J. Kouvetakis, and J. Menéndez, “Optical critical points of thin-film Ge1-ySny alloys: a comparative Ge1-ySny/Ge1-xSix study,” Phys. Rev. B 73(12), 125207 (2006).
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Canonico, M.

V. R. D’Costa, C. S. Cook, A. G. Birdwell, C. L. Littler, M. Canonico, S. Zollner, J. Kouvetakis, and J. Menéndez, “Optical critical points of thin-film Ge1-ySny alloys: a comparative Ge1-ySny/Ge1-xSix study,” Phys. Rev. B 73(12), 125207 (2006).
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M. Beals, J. Michel, J. F. Liu, D. H. Ahn, D. Sparacin, R. Sun, C. Y. Hong, L. C. Kimerling, A. Pomerene, D. Carathers, J. Beattie, A. Kopa, and A. Apsel, “Process flow innovations for photonic device integration in CMOS,” Proc. SPIE 6898, 689804 (2008).
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Chen, L. J.

C. H. Yu, P. H. Yeh, S. L. Cheng, L. J. Chen, and L. W. Cheng, “Metal-induced crystallization of amorphous Si1-xGex by rapid thermal annealing,” Thin Solid Films 469–470, 356–360 (2004).
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R. Chen, H. Lin, Y. Huo, C. Hitzman, T. I. Kamins, and J. S. Harris, “Increased photoluminescence of strain-reduced, high-Sn composition Ge1−xSnx alloys grown by molecular beam epitaxy,” Appl. Phys. Lett. 99(18), 181125 (2011).
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J. F. Liu, M. Beals, A. Pomerene, S. Bernardis, R. Sun, J. Cheng, L. C. Kimerling, and J. Michel, “Waveguide-integrated, ultra-low energy GeSi electro-absorption modulators,” Nat. Photonics 2(7), 433–437 (2008).
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C. H. Yu, P. H. Yeh, S. L. Cheng, L. J. Chen, and L. W. Cheng, “Metal-induced crystallization of amorphous Si1-xGex by rapid thermal annealing,” Thin Solid Films 469–470, 356–360 (2004).
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C. H. Yu, P. H. Yeh, S. L. Cheng, L. J. Chen, and L. W. Cheng, “Metal-induced crystallization of amorphous Si1-xGex by rapid thermal annealing,” Thin Solid Films 469–470, 356–360 (2004).
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R. Roucka, Y.-Y. Fang, J. Kouvetakis, A. V. G. Chizmeshya, and J. Menéndez, “Thermal expansivity of Ge1-ySny alloys,” Phys. Rev. B 81(24), 245214 (2010).
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W. Choi, A. T. Findikoglu, M. J. Romero, and M. Al-Jassim, “Effect of grain alignment on lateral carrier transport in aligned-crystalline silicon films on polycrystalline substrates,” J. Mater. Res. 22(04), 821–825 (2007).
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V. R. D’Costa, C. S. Cook, A. G. Birdwell, C. L. Littler, M. Canonico, S. Zollner, J. Kouvetakis, and J. Menéndez, “Optical critical points of thin-film Ge1-ySny alloys: a comparative Ge1-ySny/Ge1-xSix study,” Phys. Rev. B 73(12), 125207 (2006).
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R. A. Soref, J. Kouvetakis, J. Tolle, J. Menendez, and V. D’Costa, “Advances in SiGeSn technology,” J. Mater. Res. 22(12), 3281–3291 (2007).
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D’Costa, V. R.

V. R. D’Costa, J. Tolle, R. Roucka, J. Kouvetakis, and J. Menendez, “Raman scattering in Ge1-ySny alloys,” Solid State Commun. 144(5-6), 240–244 (2007).
[Crossref]

V. R. D’Costa, C. S. Cook, A. G. Birdwell, C. L. Littler, M. Canonico, S. Zollner, J. Kouvetakis, and J. Menéndez, “Optical critical points of thin-film Ge1-ySny alloys: a comparative Ge1-ySny/Ge1-xSix study,” Phys. Rev. B 73(12), 125207 (2006).
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W. Guter, J. Schöne, S. P. Philipps, M. Steiner, G. Siefer, A. Wekkeli, E. Welser, E. Oliva, A. W. Bett, and F. Dimroth, “Current-matched triple-junction solar cell reaching 41.1% conversion efficiency under concentrated sunlight,” Appl. Phys. Lett. 94(22), 223504 (2009).
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F. Dimroth and S. Kurtz, “High-efficiency multijunction solar cells,” MRS Bull. 32(03), 230–235 (2007).
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K. McComber, X. Duan, J. F. Liu, J. Michel, and L. C. Kimerling, “Single-crystal germanium growth on amorphous silicon,” Adv. Funct. Mater. 22(5), 1048–1057 (2012).
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R. Roucka, Y.-Y. Fang, J. Kouvetakis, A. V. G. Chizmeshya, and J. Menéndez, “Thermal expansivity of Ge1-ySny alloys,” Phys. Rev. B 81(24), 245214 (2010).
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W. Choi, A. T. Findikoglu, M. J. Romero, and M. Al-Jassim, “Effect of grain alignment on lateral carrier transport in aligned-crystalline silicon films on polycrystalline substrates,” J. Mater. Res. 22(04), 821–825 (2007).
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W. Guter, J. Schöne, S. P. Philipps, M. Steiner, G. Siefer, A. Wekkeli, E. Welser, E. Oliva, A. W. Bett, and F. Dimroth, “Current-matched triple-junction solar cell reaching 41.1% conversion efficiency under concentrated sunlight,” Appl. Phys. Lett. 94(22), 223504 (2009).
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A. Frova and P. Handler, “Franz-Keldysh effect in the space-charge region of a germanium p-n junction,” Phys. Rev. 137(6A), A1857–A1862 (1965).
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R. Chen, H. Lin, Y. Huo, C. Hitzman, T. I. Kamins, and J. S. Harris, “Increased photoluminescence of strain-reduced, high-Sn composition Ge1−xSnx alloys grown by molecular beam epitaxy,” Appl. Phys. Lett. 99(18), 181125 (2011).
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R. Chen, H. Lin, Y. Huo, C. Hitzman, T. I. Kamins, and J. S. Harris, “Increased photoluminescence of strain-reduced, high-Sn composition Ge1−xSnx alloys grown by molecular beam epitaxy,” Appl. Phys. Lett. 99(18), 181125 (2011).
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Hong, C. Y.

M. Beals, J. Michel, J. F. Liu, D. H. Ahn, D. Sparacin, R. Sun, C. Y. Hong, L. C. Kimerling, A. Pomerene, D. Carathers, J. Beattie, A. Kopa, and A. Apsel, “Process flow innovations for photonic device integration in CMOS,” Proc. SPIE 6898, 689804 (2008).
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D. H. Ahn, C. Y. Hong, J. F. Liu, W. Giziewicz, M. Beals, L. C. Kimerling, J. Michel, J. Chen, and F. X. Kärtner, “High performance, waveguide integrated Ge photodetectors,” Opt. Express 15(7), 3916–3921 (2007).
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R. Chen, H. Lin, Y. Huo, C. Hitzman, T. I. Kamins, and J. S. Harris, “Increased photoluminescence of strain-reduced, high-Sn composition Ge1−xSnx alloys grown by molecular beam epitaxy,” Appl. Phys. Lett. 99(18), 181125 (2011).
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R. Chen, H. Lin, Y. Huo, C. Hitzman, T. I. Kamins, and J. S. Harris, “Increased photoluminescence of strain-reduced, high-Sn composition Ge1−xSnx alloys grown by molecular beam epitaxy,” Appl. Phys. Lett. 99(18), 181125 (2011).
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H. Kanno, K. Atsushi, T. Sadoh, and M. Miyao, “Ge-enhanced MILC velocity in a-Ge/a-Si/SiO2layered structure,” Mater. Sci. Semicond. Process. 8(1-3), 83–88 (2005).
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Kaschel, M.

J. Werner, M. Oehme, M. Schmid, M. Kaschel, A. Schirmer, E. Kasper, and J. Schulze, “Germanium-tin p-i-n photodetectors integrated on silicon grown by molecular beam epitaxy,” Appl. Phys. Lett. 98(6), 061108 (2011).
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J. Werner, M. Oehme, M. Schmid, M. Kaschel, A. Schirmer, E. Kasper, and J. Schulze, “Germanium-tin p-i-n photodetectors integrated on silicon grown by molecular beam epitaxy,” Appl. Phys. Lett. 98(6), 061108 (2011).
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Kimerling, L. C.

K. McComber, X. Duan, J. F. Liu, J. Michel, and L. C. Kimerling, “Single-crystal germanium growth on amorphous silicon,” Adv. Funct. Mater. 22(5), 1048–1057 (2012).
[Crossref]

J. F. Liu, X. C. Sun, R. Camacho-Aguilera, L. C. Kimerling, and J. Michel, “Ge-on-Si laser operating at room temperature,” Opt. Lett. 35(5), 679–681 (2010).
[Crossref] [PubMed]

J. F. Liu, X. Sun, L. C. Kimerling, and J. Michel, “Direct-gap optical gain of Ge on Si at room temperature,” Opt. Lett. 34(11), 1738–1740 (2009).
[Crossref] [PubMed]

M. Beals, J. Michel, J. F. Liu, D. H. Ahn, D. Sparacin, R. Sun, C. Y. Hong, L. C. Kimerling, A. Pomerene, D. Carathers, J. Beattie, A. Kopa, and A. Apsel, “Process flow innovations for photonic device integration in CMOS,” Proc. SPIE 6898, 689804 (2008).
[Crossref]

J. F. Liu, M. Beals, A. Pomerene, S. Bernardis, R. Sun, J. Cheng, L. C. Kimerling, and J. Michel, “Waveguide-integrated, ultra-low energy GeSi electro-absorption modulators,” Nat. Photonics 2(7), 433–437 (2008).
[Crossref]

D. H. Ahn, C. Y. Hong, J. F. Liu, W. Giziewicz, M. Beals, L. C. Kimerling, J. Michel, J. Chen, and F. X. Kärtner, “High performance, waveguide integrated Ge photodetectors,” Opt. Express 15(7), 3916–3921 (2007).
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R. Kirchain and L. C. Kimerling, “A roadmap for nanophotonics,” Nat. Photonics 1(6), 303–305 (2007).
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Kopa, A.

M. Beals, J. Michel, J. F. Liu, D. H. Ahn, D. Sparacin, R. Sun, C. Y. Hong, L. C. Kimerling, A. Pomerene, D. Carathers, J. Beattie, A. Kopa, and A. Apsel, “Process flow innovations for photonic device integration in CMOS,” Proc. SPIE 6898, 689804 (2008).
[Crossref]

Koshchanov, É. A.

A. S. Saidov, A. Sh. Razzakov, and É. A. Koshchanov, “Liquid phase epitaxy of Ge1-xSnx thin fims,” Tech. Phys. Lett. 27(8), 698–700 (2001).
[Crossref]

Kouvetakis, J.

R. Roucka, J. Mathews, R. T. Beeler, J. Tolle, J. Kouvetakis, and J. Menéndez, “Direct gap electroluminescence from Si/Ge1-ySny p-i-n heterostructure diodes,” Appl. Phys. Lett. 98(6), 061109 (2011).
[Crossref]

R. Roucka, Y.-Y. Fang, J. Kouvetakis, A. V. G. Chizmeshya, and J. Menéndez, “Thermal expansivity of Ge1-ySny alloys,” Phys. Rev. B 81(24), 245214 (2010).
[Crossref]

R. A. Soref, J. Kouvetakis, J. Tolle, J. Menendez, and V. D’Costa, “Advances in SiGeSn technology,” J. Mater. Res. 22(12), 3281–3291 (2007).
[Crossref]

V. R. D’Costa, J. Tolle, R. Roucka, J. Kouvetakis, and J. Menendez, “Raman scattering in Ge1-ySny alloys,” Solid State Commun. 144(5-6), 240–244 (2007).
[Crossref]

V. R. D’Costa, C. S. Cook, A. G. Birdwell, C. L. Littler, M. Canonico, S. Zollner, J. Kouvetakis, and J. Menéndez, “Optical critical points of thin-film Ge1-ySny alloys: a comparative Ge1-ySny/Ge1-xSix study,” Phys. Rev. B 73(12), 125207 (2006).
[Crossref]

Kurtz, S.

F. Dimroth and S. Kurtz, “High-efficiency multijunction solar cells,” MRS Bull. 32(03), 230–235 (2007).
[Crossref]

Kyotoku, B. B. C.

Lin, H.

R. Chen, H. Lin, Y. Huo, C. Hitzman, T. I. Kamins, and J. S. Harris, “Increased photoluminescence of strain-reduced, high-Sn composition Ge1−xSnx alloys grown by molecular beam epitaxy,” Appl. Phys. Lett. 99(18), 181125 (2011).
[Crossref]

Lipson, M.

Littler, C. L.

V. R. D’Costa, C. S. Cook, A. G. Birdwell, C. L. Littler, M. Canonico, S. Zollner, J. Kouvetakis, and J. Menéndez, “Optical critical points of thin-film Ge1-ySny alloys: a comparative Ge1-ySny/Ge1-xSix study,” Phys. Rev. B 73(12), 125207 (2006).
[Crossref]

Liu, J. F.

K. McComber, X. Duan, J. F. Liu, J. Michel, and L. C. Kimerling, “Single-crystal germanium growth on amorphous silicon,” Adv. Funct. Mater. 22(5), 1048–1057 (2012).
[Crossref]

J. F. Liu, X. C. Sun, R. Camacho-Aguilera, L. C. Kimerling, and J. Michel, “Ge-on-Si laser operating at room temperature,” Opt. Lett. 35(5), 679–681 (2010).
[Crossref] [PubMed]

J. F. Liu, X. Sun, L. C. Kimerling, and J. Michel, “Direct-gap optical gain of Ge on Si at room temperature,” Opt. Lett. 34(11), 1738–1740 (2009).
[Crossref] [PubMed]

M. Beals, J. Michel, J. F. Liu, D. H. Ahn, D. Sparacin, R. Sun, C. Y. Hong, L. C. Kimerling, A. Pomerene, D. Carathers, J. Beattie, A. Kopa, and A. Apsel, “Process flow innovations for photonic device integration in CMOS,” Proc. SPIE 6898, 689804 (2008).
[Crossref]

J. F. Liu, M. Beals, A. Pomerene, S. Bernardis, R. Sun, J. Cheng, L. C. Kimerling, and J. Michel, “Waveguide-integrated, ultra-low energy GeSi electro-absorption modulators,” Nat. Photonics 2(7), 433–437 (2008).
[Crossref]

D. H. Ahn, C. Y. Hong, J. F. Liu, W. Giziewicz, M. Beals, L. C. Kimerling, J. Michel, J. Chen, and F. X. Kärtner, “High performance, waveguide integrated Ge photodetectors,” Opt. Express 15(7), 3916–3921 (2007).
[Crossref] [PubMed]

Mathews, J.

R. Roucka, J. Mathews, R. T. Beeler, J. Tolle, J. Kouvetakis, and J. Menéndez, “Direct gap electroluminescence from Si/Ge1-ySny p-i-n heterostructure diodes,” Appl. Phys. Lett. 98(6), 061109 (2011).
[Crossref]

McComber, K.

K. McComber, X. Duan, J. F. Liu, J. Michel, and L. C. Kimerling, “Single-crystal germanium growth on amorphous silicon,” Adv. Funct. Mater. 22(5), 1048–1057 (2012).
[Crossref]

Menendez, J.

V. R. D’Costa, J. Tolle, R. Roucka, J. Kouvetakis, and J. Menendez, “Raman scattering in Ge1-ySny alloys,” Solid State Commun. 144(5-6), 240–244 (2007).
[Crossref]

R. A. Soref, J. Kouvetakis, J. Tolle, J. Menendez, and V. D’Costa, “Advances in SiGeSn technology,” J. Mater. Res. 22(12), 3281–3291 (2007).
[Crossref]

Menéndez, J.

R. Roucka, J. Mathews, R. T. Beeler, J. Tolle, J. Kouvetakis, and J. Menéndez, “Direct gap electroluminescence from Si/Ge1-ySny p-i-n heterostructure diodes,” Appl. Phys. Lett. 98(6), 061109 (2011).
[Crossref]

R. Roucka, Y.-Y. Fang, J. Kouvetakis, A. V. G. Chizmeshya, and J. Menéndez, “Thermal expansivity of Ge1-ySny alloys,” Phys. Rev. B 81(24), 245214 (2010).
[Crossref]

V. R. D’Costa, C. S. Cook, A. G. Birdwell, C. L. Littler, M. Canonico, S. Zollner, J. Kouvetakis, and J. Menéndez, “Optical critical points of thin-film Ge1-ySny alloys: a comparative Ge1-ySny/Ge1-xSix study,” Phys. Rev. B 73(12), 125207 (2006).
[Crossref]

Michel, J.

K. McComber, X. Duan, J. F. Liu, J. Michel, and L. C. Kimerling, “Single-crystal germanium growth on amorphous silicon,” Adv. Funct. Mater. 22(5), 1048–1057 (2012).
[Crossref]

J. F. Liu, X. C. Sun, R. Camacho-Aguilera, L. C. Kimerling, and J. Michel, “Ge-on-Si laser operating at room temperature,” Opt. Lett. 35(5), 679–681 (2010).
[Crossref] [PubMed]

J. F. Liu, X. Sun, L. C. Kimerling, and J. Michel, “Direct-gap optical gain of Ge on Si at room temperature,” Opt. Lett. 34(11), 1738–1740 (2009).
[Crossref] [PubMed]

M. Beals, J. Michel, J. F. Liu, D. H. Ahn, D. Sparacin, R. Sun, C. Y. Hong, L. C. Kimerling, A. Pomerene, D. Carathers, J. Beattie, A. Kopa, and A. Apsel, “Process flow innovations for photonic device integration in CMOS,” Proc. SPIE 6898, 689804 (2008).
[Crossref]

J. F. Liu, M. Beals, A. Pomerene, S. Bernardis, R. Sun, J. Cheng, L. C. Kimerling, and J. Michel, “Waveguide-integrated, ultra-low energy GeSi electro-absorption modulators,” Nat. Photonics 2(7), 433–437 (2008).
[Crossref]

D. H. Ahn, C. Y. Hong, J. F. Liu, W. Giziewicz, M. Beals, L. C. Kimerling, J. Michel, J. Chen, and F. X. Kärtner, “High performance, waveguide integrated Ge photodetectors,” Opt. Express 15(7), 3916–3921 (2007).
[Crossref] [PubMed]

Miyao, M.

H. Kanno, K. Atsushi, T. Sadoh, and M. Miyao, “Ge-enhanced MILC velocity in a-Ge/a-Si/SiO2layered structure,” Mater. Sci. Semicond. Process. 8(1-3), 83–88 (2005).
[Crossref]

Navarro-Contreras, H.

H. Pérez Ladrón de Guevara, A. G. Rodríguez, H. Navarro-Contreras, and M. A. Vidal, “Ge1-xSnx alloys pseudomorphically grown on Ge(001),” Appl. Phys. Lett. 83(24), 4942–4944 (2003).
[Crossref]

Oehme, M.

J. Werner, M. Oehme, M. Schmid, M. Kaschel, A. Schirmer, E. Kasper, and J. Schulze, “Germanium-tin p-i-n photodetectors integrated on silicon grown by molecular beam epitaxy,” Appl. Phys. Lett. 98(6), 061108 (2011).
[Crossref]

Oliva, E.

W. Guter, J. Schöne, S. P. Philipps, M. Steiner, G. Siefer, A. Wekkeli, E. Welser, E. Oliva, A. W. Bett, and F. Dimroth, “Current-matched triple-junction solar cell reaching 41.1% conversion efficiency under concentrated sunlight,” Appl. Phys. Lett. 94(22), 223504 (2009).
[Crossref]

Pérez Ladrón de Guevara, H.

H. Pérez Ladrón de Guevara, A. G. Rodríguez, H. Navarro-Contreras, and M. A. Vidal, “Ge1-xSnx alloys pseudomorphically grown on Ge(001),” Appl. Phys. Lett. 83(24), 4942–4944 (2003).
[Crossref]

Philipps, S. P.

W. Guter, J. Schöne, S. P. Philipps, M. Steiner, G. Siefer, A. Wekkeli, E. Welser, E. Oliva, A. W. Bett, and F. Dimroth, “Current-matched triple-junction solar cell reaching 41.1% conversion efficiency under concentrated sunlight,” Appl. Phys. Lett. 94(22), 223504 (2009).
[Crossref]

Pomerene, A.

J. F. Liu, M. Beals, A. Pomerene, S. Bernardis, R. Sun, J. Cheng, L. C. Kimerling, and J. Michel, “Waveguide-integrated, ultra-low energy GeSi electro-absorption modulators,” Nat. Photonics 2(7), 433–437 (2008).
[Crossref]

M. Beals, J. Michel, J. F. Liu, D. H. Ahn, D. Sparacin, R. Sun, C. Y. Hong, L. C. Kimerling, A. Pomerene, D. Carathers, J. Beattie, A. Kopa, and A. Apsel, “Process flow innovations for photonic device integration in CMOS,” Proc. SPIE 6898, 689804 (2008).
[Crossref]

Razzakov, A. Sh.

A. S. Saidov, A. Sh. Razzakov, and É. A. Koshchanov, “Liquid phase epitaxy of Ge1-xSnx thin fims,” Tech. Phys. Lett. 27(8), 698–700 (2001).
[Crossref]

Rodríguez, A. G.

H. Pérez Ladrón de Guevara, A. G. Rodríguez, H. Navarro-Contreras, and M. A. Vidal, “Ge1-xSnx alloys pseudomorphically grown on Ge(001),” Appl. Phys. Lett. 83(24), 4942–4944 (2003).
[Crossref]

Romero, M. J.

W. Choi, A. T. Findikoglu, M. J. Romero, and M. Al-Jassim, “Effect of grain alignment on lateral carrier transport in aligned-crystalline silicon films on polycrystalline substrates,” J. Mater. Res. 22(04), 821–825 (2007).
[Crossref]

Roucka, R.

R. Roucka, J. Mathews, R. T. Beeler, J. Tolle, J. Kouvetakis, and J. Menéndez, “Direct gap electroluminescence from Si/Ge1-ySny p-i-n heterostructure diodes,” Appl. Phys. Lett. 98(6), 061109 (2011).
[Crossref]

R. Roucka, Y.-Y. Fang, J. Kouvetakis, A. V. G. Chizmeshya, and J. Menéndez, “Thermal expansivity of Ge1-ySny alloys,” Phys. Rev. B 81(24), 245214 (2010).
[Crossref]

V. R. D’Costa, J. Tolle, R. Roucka, J. Kouvetakis, and J. Menendez, “Raman scattering in Ge1-ySny alloys,” Solid State Commun. 144(5-6), 240–244 (2007).
[Crossref]

Sadoh, T.

H. Kanno, K. Atsushi, T. Sadoh, and M. Miyao, “Ge-enhanced MILC velocity in a-Ge/a-Si/SiO2layered structure,” Mater. Sci. Semicond. Process. 8(1-3), 83–88 (2005).
[Crossref]

Saidov, A. S.

A. S. Saidov, A. Sh. Razzakov, and É. A. Koshchanov, “Liquid phase epitaxy of Ge1-xSnx thin fims,” Tech. Phys. Lett. 27(8), 698–700 (2001).
[Crossref]

Schirmer, A.

J. Werner, M. Oehme, M. Schmid, M. Kaschel, A. Schirmer, E. Kasper, and J. Schulze, “Germanium-tin p-i-n photodetectors integrated on silicon grown by molecular beam epitaxy,” Appl. Phys. Lett. 98(6), 061108 (2011).
[Crossref]

Schmid, M.

J. Werner, M. Oehme, M. Schmid, M. Kaschel, A. Schirmer, E. Kasper, and J. Schulze, “Germanium-tin p-i-n photodetectors integrated on silicon grown by molecular beam epitaxy,” Appl. Phys. Lett. 98(6), 061108 (2011).
[Crossref]

Schöne, J.

W. Guter, J. Schöne, S. P. Philipps, M. Steiner, G. Siefer, A. Wekkeli, E. Welser, E. Oliva, A. W. Bett, and F. Dimroth, “Current-matched triple-junction solar cell reaching 41.1% conversion efficiency under concentrated sunlight,” Appl. Phys. Lett. 94(22), 223504 (2009).
[Crossref]

Schulze, J.

J. Werner, M. Oehme, M. Schmid, M. Kaschel, A. Schirmer, E. Kasper, and J. Schulze, “Germanium-tin p-i-n photodetectors integrated on silicon grown by molecular beam epitaxy,” Appl. Phys. Lett. 98(6), 061108 (2011).
[Crossref]

Siefer, G.

W. Guter, J. Schöne, S. P. Philipps, M. Steiner, G. Siefer, A. Wekkeli, E. Welser, E. Oliva, A. W. Bett, and F. Dimroth, “Current-matched triple-junction solar cell reaching 41.1% conversion efficiency under concentrated sunlight,” Appl. Phys. Lett. 94(22), 223504 (2009).
[Crossref]

Soref, R. A.

R. A. Soref, J. Kouvetakis, J. Tolle, J. Menendez, and V. D’Costa, “Advances in SiGeSn technology,” J. Mater. Res. 22(12), 3281–3291 (2007).
[Crossref]

R. A. Soref, “The past, present, and future of silicon photonics,” IEEE Sel. Top. Quantum. Electron. 12(6), 1678–1687 (2006).
[Crossref]

R. A. Soref and L. Friedman, “Direct gap Ge/GeSn/Si and GeSn/Ge/Si heterostructures,” Superlattices Microstruct. 14(2-3), 189–193 (1993).
[Crossref]

Sparacin, D.

M. Beals, J. Michel, J. F. Liu, D. H. Ahn, D. Sparacin, R. Sun, C. Y. Hong, L. C. Kimerling, A. Pomerene, D. Carathers, J. Beattie, A. Kopa, and A. Apsel, “Process flow innovations for photonic device integration in CMOS,” Proc. SPIE 6898, 689804 (2008).
[Crossref]

Steiner, M.

W. Guter, J. Schöne, S. P. Philipps, M. Steiner, G. Siefer, A. Wekkeli, E. Welser, E. Oliva, A. W. Bett, and F. Dimroth, “Current-matched triple-junction solar cell reaching 41.1% conversion efficiency under concentrated sunlight,” Appl. Phys. Lett. 94(22), 223504 (2009).
[Crossref]

Sun, R.

M. Beals, J. Michel, J. F. Liu, D. H. Ahn, D. Sparacin, R. Sun, C. Y. Hong, L. C. Kimerling, A. Pomerene, D. Carathers, J. Beattie, A. Kopa, and A. Apsel, “Process flow innovations for photonic device integration in CMOS,” Proc. SPIE 6898, 689804 (2008).
[Crossref]

J. F. Liu, M. Beals, A. Pomerene, S. Bernardis, R. Sun, J. Cheng, L. C. Kimerling, and J. Michel, “Waveguide-integrated, ultra-low energy GeSi electro-absorption modulators,” Nat. Photonics 2(7), 433–437 (2008).
[Crossref]

Sun, X.

Sun, X. C.

Tolle, J.

R. Roucka, J. Mathews, R. T. Beeler, J. Tolle, J. Kouvetakis, and J. Menéndez, “Direct gap electroluminescence from Si/Ge1-ySny p-i-n heterostructure diodes,” Appl. Phys. Lett. 98(6), 061109 (2011).
[Crossref]

R. A. Soref, J. Kouvetakis, J. Tolle, J. Menendez, and V. D’Costa, “Advances in SiGeSn technology,” J. Mater. Res. 22(12), 3281–3291 (2007).
[Crossref]

V. R. D’Costa, J. Tolle, R. Roucka, J. Kouvetakis, and J. Menendez, “Raman scattering in Ge1-ySny alloys,” Solid State Commun. 144(5-6), 240–244 (2007).
[Crossref]

Van de Walle, C. G.

C. G. Van de Walle, “Band lineups and deformation potentials in the model-solid theory,” Phys. Rev. B Condens. Matter 39(3), 1871–1883 (1989).
[Crossref] [PubMed]

Vidal, M. A.

H. Pérez Ladrón de Guevara, A. G. Rodríguez, H. Navarro-Contreras, and M. A. Vidal, “Ge1-xSnx alloys pseudomorphically grown on Ge(001),” Appl. Phys. Lett. 83(24), 4942–4944 (2003).
[Crossref]

Wekkeli, A.

W. Guter, J. Schöne, S. P. Philipps, M. Steiner, G. Siefer, A. Wekkeli, E. Welser, E. Oliva, A. W. Bett, and F. Dimroth, “Current-matched triple-junction solar cell reaching 41.1% conversion efficiency under concentrated sunlight,” Appl. Phys. Lett. 94(22), 223504 (2009).
[Crossref]

Welser, E.

W. Guter, J. Schöne, S. P. Philipps, M. Steiner, G. Siefer, A. Wekkeli, E. Welser, E. Oliva, A. W. Bett, and F. Dimroth, “Current-matched triple-junction solar cell reaching 41.1% conversion efficiency under concentrated sunlight,” Appl. Phys. Lett. 94(22), 223504 (2009).
[Crossref]

Werner, J.

J. Werner, M. Oehme, M. Schmid, M. Kaschel, A. Schirmer, E. Kasper, and J. Schulze, “Germanium-tin p-i-n photodetectors integrated on silicon grown by molecular beam epitaxy,” Appl. Phys. Lett. 98(6), 061108 (2011).
[Crossref]

Yang, C. M.

C. M. Yang and H. A. Atwater, “Selective solid phase crystallization for control of grain size and location in Ge thin films on silicon dioxide,” Appl. Phys. Lett. 68(24), 3392–3394 (1996).
[Crossref]

Yeh, P. H.

C. H. Yu, P. H. Yeh, S. L. Cheng, L. J. Chen, and L. W. Cheng, “Metal-induced crystallization of amorphous Si1-xGex by rapid thermal annealing,” Thin Solid Films 469–470, 356–360 (2004).
[Crossref]

Yu, C. H.

C. H. Yu, P. H. Yeh, S. L. Cheng, L. J. Chen, and L. W. Cheng, “Metal-induced crystallization of amorphous Si1-xGex by rapid thermal annealing,” Thin Solid Films 469–470, 356–360 (2004).
[Crossref]

Zollner, S.

V. R. D’Costa, C. S. Cook, A. G. Birdwell, C. L. Littler, M. Canonico, S. Zollner, J. Kouvetakis, and J. Menéndez, “Optical critical points of thin-film Ge1-ySny alloys: a comparative Ge1-ySny/Ge1-xSix study,” Phys. Rev. B 73(12), 125207 (2006).
[Crossref]

Adv. Funct. Mater. (1)

K. McComber, X. Duan, J. F. Liu, J. Michel, and L. C. Kimerling, “Single-crystal germanium growth on amorphous silicon,” Adv. Funct. Mater. 22(5), 1048–1057 (2012).
[Crossref]

Appl. Phys. Lett. (6)

J. Werner, M. Oehme, M. Schmid, M. Kaschel, A. Schirmer, E. Kasper, and J. Schulze, “Germanium-tin p-i-n photodetectors integrated on silicon grown by molecular beam epitaxy,” Appl. Phys. Lett. 98(6), 061108 (2011).
[Crossref]

R. Roucka, J. Mathews, R. T. Beeler, J. Tolle, J. Kouvetakis, and J. Menéndez, “Direct gap electroluminescence from Si/Ge1-ySny p-i-n heterostructure diodes,” Appl. Phys. Lett. 98(6), 061109 (2011).
[Crossref]

C. M. Yang and H. A. Atwater, “Selective solid phase crystallization for control of grain size and location in Ge thin films on silicon dioxide,” Appl. Phys. Lett. 68(24), 3392–3394 (1996).
[Crossref]

R. Chen, H. Lin, Y. Huo, C. Hitzman, T. I. Kamins, and J. S. Harris, “Increased photoluminescence of strain-reduced, high-Sn composition Ge1−xSnx alloys grown by molecular beam epitaxy,” Appl. Phys. Lett. 99(18), 181125 (2011).
[Crossref]

W. Guter, J. Schöne, S. P. Philipps, M. Steiner, G. Siefer, A. Wekkeli, E. Welser, E. Oliva, A. W. Bett, and F. Dimroth, “Current-matched triple-junction solar cell reaching 41.1% conversion efficiency under concentrated sunlight,” Appl. Phys. Lett. 94(22), 223504 (2009).
[Crossref]

H. Pérez Ladrón de Guevara, A. G. Rodríguez, H. Navarro-Contreras, and M. A. Vidal, “Ge1-xSnx alloys pseudomorphically grown on Ge(001),” Appl. Phys. Lett. 83(24), 4942–4944 (2003).
[Crossref]

IEEE Sel. Top. Quantum. Electron. (1)

R. A. Soref, “The past, present, and future of silicon photonics,” IEEE Sel. Top. Quantum. Electron. 12(6), 1678–1687 (2006).
[Crossref]

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R. J. Jaccodine, “Surface Energy of Germanium and Silicon,” J. Electrochem. Soc. 110(6), 524–527 (1963).
[Crossref]

J. Mater. Res. (2)

R. A. Soref, J. Kouvetakis, J. Tolle, J. Menendez, and V. D’Costa, “Advances in SiGeSn technology,” J. Mater. Res. 22(12), 3281–3291 (2007).
[Crossref]

W. Choi, A. T. Findikoglu, M. J. Romero, and M. Al-Jassim, “Effect of grain alignment on lateral carrier transport in aligned-crystalline silicon films on polycrystalline substrates,” J. Mater. Res. 22(04), 821–825 (2007).
[Crossref]

Mater. Sci. Semicond. Process. (1)

H. Kanno, K. Atsushi, T. Sadoh, and M. Miyao, “Ge-enhanced MILC velocity in a-Ge/a-Si/SiO2layered structure,” Mater. Sci. Semicond. Process. 8(1-3), 83–88 (2005).
[Crossref]

MRS Bull. (1)

F. Dimroth and S. Kurtz, “High-efficiency multijunction solar cells,” MRS Bull. 32(03), 230–235 (2007).
[Crossref]

Nat. Photonics (2)

R. Kirchain and L. C. Kimerling, “A roadmap for nanophotonics,” Nat. Photonics 1(6), 303–305 (2007).
[Crossref]

J. F. Liu, M. Beals, A. Pomerene, S. Bernardis, R. Sun, J. Cheng, L. C. Kimerling, and J. Michel, “Waveguide-integrated, ultra-low energy GeSi electro-absorption modulators,” Nat. Photonics 2(7), 433–437 (2008).
[Crossref]

Opt. Express (3)

Opt. Lett. (2)

Phys. Rev. (1)

A. Frova and P. Handler, “Franz-Keldysh effect in the space-charge region of a germanium p-n junction,” Phys. Rev. 137(6A), A1857–A1862 (1965).
[Crossref]

Phys. Rev. B (2)

R. Roucka, Y.-Y. Fang, J. Kouvetakis, A. V. G. Chizmeshya, and J. Menéndez, “Thermal expansivity of Ge1-ySny alloys,” Phys. Rev. B 81(24), 245214 (2010).
[Crossref]

V. R. D’Costa, C. S. Cook, A. G. Birdwell, C. L. Littler, M. Canonico, S. Zollner, J. Kouvetakis, and J. Menéndez, “Optical critical points of thin-film Ge1-ySny alloys: a comparative Ge1-ySny/Ge1-xSix study,” Phys. Rev. B 73(12), 125207 (2006).
[Crossref]

Phys. Rev. B Condens. Matter (1)

C. G. Van de Walle, “Band lineups and deformation potentials in the model-solid theory,” Phys. Rev. B Condens. Matter 39(3), 1871–1883 (1989).
[Crossref] [PubMed]

Phys. Rev. Lett. (1)

G. He and H. A. Atwater, “Interband transitions in SnxGe1-x alloys,” Phys. Rev. Lett. 79(10), 1937–1940 (1997).
[Crossref]

Proc. SPIE (1)

M. Beals, J. Michel, J. F. Liu, D. H. Ahn, D. Sparacin, R. Sun, C. Y. Hong, L. C. Kimerling, A. Pomerene, D. Carathers, J. Beattie, A. Kopa, and A. Apsel, “Process flow innovations for photonic device integration in CMOS,” Proc. SPIE 6898, 689804 (2008).
[Crossref]

Solid State Commun. (1)

V. R. D’Costa, J. Tolle, R. Roucka, J. Kouvetakis, and J. Menendez, “Raman scattering in Ge1-ySny alloys,” Solid State Commun. 144(5-6), 240–244 (2007).
[Crossref]

Superlattices Microstruct. (1)

R. A. Soref and L. Friedman, “Direct gap Ge/GeSn/Si and GeSn/Ge/Si heterostructures,” Superlattices Microstruct. 14(2-3), 189–193 (1993).
[Crossref]

Tech. Phys. Lett. (1)

A. S. Saidov, A. Sh. Razzakov, and É. A. Koshchanov, “Liquid phase epitaxy of Ge1-xSnx thin fims,” Tech. Phys. Lett. 27(8), 698–700 (2001).
[Crossref]

Thin Solid Films (1)

C. H. Yu, P. H. Yeh, S. L. Cheng, L. J. Chen, and L. W. Cheng, “Metal-induced crystallization of amorphous Si1-xGex by rapid thermal annealing,” Thin Solid Films 469–470, 356–360 (2004).
[Crossref]

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S. Gupta, B. Vincent, B. Yang, D. Lin, F. Gencarelli, J.-Y. J. Lin, R. Chen, O. Richard, H. Bender, B. Magyari-Köpe, M. Caymax, J. Dekoster, Y. Nishi, and K. C. Saraswat, “Towards high mobility GeSn channel nMOSFETs: Improved surface passivation using novel ozone oxidation method,” in Proceedings of IEEE Electronic Device Meeting (Institute of Electrical and Electronics Engineers, San Francisco, 2012), pp. 16.2.1–16.2.4.
[Crossref]

J. M. Fedeli, M. Migette, L. Di Cioccio, L. El Melhaoui, R. Orobtchouk, C. Seassal, P. Rojoromeo, F. Mandorlo, D. Marris Morini, and L. Vivien, “Incorporation of a photonic layer at the metallization levels of a CMOS circuit,” in Proceedings of IEEE International Conference on Group IV Photonics (Institute of Electrical and Electronics Engineers, 2006), pp. 200–202.

K. Wada, “Challenges of Si Photonics for on-chip Integration,” in Proceedings of European Conference of Optical Communication (ECOC), (Vienna, Austria, September, 2009), paper 2.7.3.

M. G. Mauk, Liquid Phase Epitaxy of Electronic, Optical, and Optoelectronic Materials (Wiley, 2007), Chap. 5.

P. Water, Stress Analysis and Mechanical Characterization of Thin Films for Microelectronics and MEMS Applications (ProQuest, 2008), Chap. 3, pp. 78–95.

J. F. Shackelford, Introduction to Materials Science for Engineers, 5th Ed. (Prentice-Hall, 2000), Chap. 4.

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Figures (6)

Fig. 1
Fig. 1 (a) Ge-Sn equilibrium phase diagram. (b) A zoomed-in diagram on the Ge-rich side [19].
Fig. 2
Fig. 2 (a) θ-2θ XRD data of the GeSn sample with 9.5 at.% Sn annealed at 464°C in comparison to a reference pure Ge sample annealed at 660 °C, both for 30 minutes. Note that the vertical axis is in log scale. The inset shows a schematic cross-section of the GeSn sample. (b) Raman spectra of the unannealed and annealed 9.5 at.% Sn sample in comparison to a single crystal Ge reference sample. (c) Crystallization temperature and XRD peak intensity ratio of the strongest peak (111) to the second strongest peak (either (220) or (311)) as a function of the Sn atomic concentration in as-deposited a-GeSn films. The linear fit shows that the crystallization temperature decreases by ~20 °C with 1 at.% increase in the Sn composition. The strongest (111) textured is achieved at 9.5 at.% Sn.
Fig. 3
Fig. 3 (a) SEM image of the GeSn sample with 9.5 at.% Sn after annealing at 464°C for 30 minutes. The bright dots and lines are identified to be Sn segregates by EDS. (b) SEM image of the annealed 9.5 at.% Sn sample after etching away Sn segregates on the surface, leaving behind the highly textured Ge0.913Sn0.087 thin film. (c) EBSD mapping of exactly the same region as shown in (b), where different colors indicate different in-plane crystallographic orientations. Grains that are ~5 μm wide and tens of microns long are observed. The average grain size is ~10 μm (d) EBSD mapping of the GeSn sample with 14.5 at.% Sn after annealing at 410 °C and etching away the Sn precipitates. While there are more small grains present, the average grain size is still ~5 μm.
Fig. 4
Fig. 4 (a) Distribution of misorientation angles between neighboring grains derived from the EBSD data of the highly textured Ge0.913Sn0.087 thin film in Fig. 3(c). The sample is crystallized from the a-GeSn thin film with 9.5 at.% Sn. The inset shows the inverse pole figure obtained over a 0.2 × 0.2 mm2 area, confirming the strong (111) texture. (b) Distribution of misorientation angles between neighboring grains for the 14.5 at.% Sn sample after crystallization annealing and etching away the Sn segregates. The inset shows the inverse pole figure obtained from the same EBSD mapping.
Fig. 5
Fig. 5 (a) Large-area SEM image of the highly textured Ge0.913Sn0.087 thin film previously shown in Figs. 3(b) and 3(c). The sample is crystallized from a-GeSn with 9.5 at.% Sn. The arrows point to 6 nucleation centers in an total area of ~1.6 mm2, from which GeSn grains grow radially. (b) A zoomed-in image of domain 2 in (a). (c) Large-area SEM image of the 14.5 at.% Sn sample after crystallization annealing and etching away Sn segregates. The radiating dendritic feature is still present, but the density of nucleation centers is increased compared to the 9.5 at. % Sn sample shown in (a) and (b). (d) Large-area SEM image of the 16.5 at.% Sn sample after crystallization annealing and etching away Sn segregates. The radiating dendritic feature is no longer present.
Fig. 6
Fig. 6 (a) Transmittance spectrum of the high crystallinity Ge0.913Sn0.087 thin film sample compared to a reference sample without the GeSn thin film. (b) Absorption spectrum of Ge0.913Sn0.087 derived from the transmittance spectrum in (a).

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