Open Access
Add to BibSonomy
Abstract
Silicon avalanche light-emitting devices (Si Av LEDs) offer various possibilities for realizing micro- and even nano- optical biosensors directly on chip. The light-emitting devices (LEDs) operate in the wavelength range of about 450-850nm, and their optical power emitted is of the order of a few hundreds of nW/µm2. These LEDs could be fabricated in micro- and nano- dimensions by using modern semiconductor fabrication processing technologies through the mainstream of silicon material. Through a series of experiments, the dispersion phenomena in the Si Av LED are observed. Also, its light emission point was proved to locate at about one micron just below the silicon-silicon oxide interface. Subsequently, a micro-fluidic channel sensor was designed by using the dispersion characteristics owned by the Si Av LED. The analytes flowing through a micro-fluidic channel could be studied by their specific transmittance and absorption spectra. Moreover, simulations verify that a novel designed waveguide-based sensor could be fabricated on chip between the Si optical source and the Si P-I-N detector.
© 2019 Optical Society of America under the terms of the OSA Open Access Publishing Agreement
1. Introduction
Biosensors and lab on chip devices have become a subject of growing professional interest world-wide. This is evident in the growing number of scientific publications, and the astronomical growth in world market for biosensors and lab-on chip devices over the past ten years [1–9]. With the innovation of biomaterials such as conducting polymers, copolymers and sol gels, these devices could largely miniaturize biological analyses in an integrated chip with new generation sensors. Due to the maturity of device fabrication processing technology, standard silicon integrated technologies could greatly reduce costs, while biosensor devices are being miniaturized into micro- and even nano- dimensions. Various attempts have been tried to use the material of silicon for manufacturing the components like light emitter, waveguide, and detector, in particular how to integrate these components on a single silicon substrate via the standard semiconductor manufacturing processing technology such as CMOS and RF bipolar technologies [10–13].
Through recent research, light emission from silicon devices has been realized in various types of device structures with the principle of p-n junction reverse-biased toward avalanche. This development has now been named as “Silicon Light Emitting Diodes that operate in the reverse Avalanche Mode” (Si-AMLEDs) [14–18]. It is believed that, if the detailed dispersion characteristics observed per solid angle for a particular device is known, the design of novel and futuristic on-chip electro-optic applications can be realized. Potential applications include wavelength multiplexers for on-chip communication, diverse futuristic on chip micro- and nano- dimensioned gas sensors and even on-chip biosensors [19–24].
In this paper, one type of Si Av LED with the device structure of two-junction micron-sized p+nn+ is applied for observing its dispersion characteristics and for analyzing the different wavelengths of light emitted from different exit angles to the normal of the surface. It can be anticipated that the particular high refractive index of Si, and since the source of the optical radiation occurs at specific micro spots located subsurface of the silicon, that particular interesting dispersion characteristics could be observed. Apparently, the technique offers various optimizations for designing specific sensors for broad applications.
2. Regarding the Si Av LEDs
To overcome the light emission weakness due to the indirect bandgap of silicon, many attempts to improve the characteristics of Si Av LED have been done. Researchers inferred that the light emission mechanism of Si Av LEDs could be attributed to phonon assisted intra-band and inter-band recombination phenomena [25–27]. A series of utilizable silicon light emitting devices were realized by means of “surface engineering” and “current density engineering” techniques in standard CMOS manufacture procedures [28–33]. Subsequently, in an avalanching Si n+p junctions, increased light emission is realized by providing additional carriers injected into the junctions [31,32]. Following that, various devices in order to further enhance the intensity of light emissions were presented. A series of CMOS integrated LED devices with a third terminal in which the gate is controlled were realized. Due to the reverse bias configuration of Si Av LEDs, inherent high modulation speed ranging into the GHz could be one of the major advantages. Efforts on increasing the emission intensities in the wavelength ranging 650-750nm are specifically done [19–24]. This is the first time that the emission could be enhanced by means of enhanced impurity scattering and extended electric field (E-field) creatively profiling with using the silicon AV LED that is fully compatible with the standard CMOS process technology. Related light emission intensities could be up to the order of about 200nW/µm2.
As shown in Fig. 1(a), one type of Si Av LED with specific p+nn+ graded junction device structure was realized in a 0.35µm Si Bipolar process with high frequency RF application capabilities. To restrict the lateral carrier diffusion and make the diffusing carrier density into maximum, a unique pillar structure was etched out on a p-type semi-insulating substrate in this process. Dopants were doped in both side of the substrate to form n+ and p+ region, the doping should keep n+ region and p+ region one micron away. Gradually, an one micron graded junction was formed with dopants overlapping each other [23,24].
Fig. 1. Device design, considerations: (a) high resolution micrograph of the Silicon Avalanche LED, fabricated through an RF bipolar-integrated circuit process. The fuscous region represent the etching into Si substrate, filled with about 4 µm thick silicon oxide as an interlayer, and a 0.5 µm thick silicon nitride layer deposited topside. (b) lateral cross-section of the device. (c) spectral characteristics of the emitted optical radiation with some prominent peaks.
The optical spectrums are measured by the Anritso MS9710B Spectrum Analyzer with a lensed-probe optical fiber, and the fibre for power collection is a multimode (MM) fibre with a core diameter of 62.5 m and a NA of ≤0.275 [34]. The spectrum analyzer has the feature to perform extensive noise reduction and to measure optical spectrums still reliable to very low emission levels. In each case, the lensed optical probe is placed directly vertically above the device and the lensed probe is electronically micro manipulated to within 0.1 mm of the light emitting device. The total emission intensities for the device, configured in Fig. 1(b) with cross-sectional conduction areas of about 1 micron square, indicate total emission intensities at the surface of the device of 200nW/µm2. Assuming the probe detection loss is of the order of 10−2, a total external power-to-light conversion efficiency of the order of 10−4 is calculated. As predicted, the internal conversion efficiencies can reach into the range of 10−3 to 10−2. It indicates the assumption is appropriately reasonable.
Figure 1(c) depicts the main spectral components as observed for avalanching junctions, representing a broad spectrum from 450 nm to 850 nm. Prominent peaks (2.3 eV, 1.8 eV and 1.5 eV) are observed in the spectrographic measurements for the devices shown in the spectrum when converting the nm emissions to corresponding eV emissions. Regarding the related physical mechanism for the light emission, the wavelength dependence of the electroluminescence and its relation with the distribution of the light-emitting centers is further discussed as follows: a) photon energies below ∼2 eV (Corresponding to wavelength longer than 620 nm) are attributed to the indirect interband process in high-field carrier populations; b) Bremsstrahlung radiation appears dominate at intermediate energies (i.e., between ∼2 eV and ∼2.3 eV or in the wavelength range of 539 nm to 620 nm); c) the mechanism can be treated as near-direct interband transition for energies beyond ∼2.3 eV (Corresponding to wavelength shorter than 539 nm) [35].
3. Analysis on wavelength dispersion through experimental observations
To analyze the wavelength dispersion phenomena that occurred in this Si Av LED more in-depth, experimental observed dispersion characteristics of the optical radiation from the silicon light source is analyzed. Particular microscope is hence essentially used as a probe to investigate the dispersion characteristics of the emitted light from the silicon device light emission as they are emitted at various angles. High resolution color images are taken at increment angles, 5, 15, 30, 45 and 60 degrees in each case. MATLAB image analyses to count the number of pixels on micrographs, while the number of red, green, blue pixels represents the optical intensity. In every condition, the measured shift of color peaks by means of centimeter order, making sure images are focused as best as possible in each case in order to align the focus point with the surface of the chip.
Intensity profiles are taken of the pixels through each profile using MATLAB image analyses. The shift in color peaks was measured in centimeter in the final digitally magnified images in each case. The results of multi-angle observation on the dispersion phenomena, as shown in Fig. 2, are representative of five separate analyses from the same device.
Fig. 2. Observed experimental dispersion characteristics (color shifts per propagation wavelength) at 5 degree, 15 degree, 30 degree, 45 degree and 60 degree for the emitted radiation from the device. The micrographs show the clear dispersion of emitted colors increasing with the tilt angle.
A clear narrow dispersion from red to yellow to green with faint tints of blue is observed at 5 degrees exit angle. A spectrum for each primary wavelength of about 5 degrees could be derived as according to the arguments based on experimental rationale, due to the numerical aperture limitations of the microscope objective in which the chip and its mount are successively tilted from the horizontal plane while the emission characteristics are recorded with a color charged-couple diode (CCD) camera. However, the dispersion in terms of different wavelength emissions per angle is very clear and pronounced. As expected, the red radiation is the least absorbed in the silicon itself and appears as strong intensity at the low exit angle, while yellow wavelength emissions appears distinctly and at strong intensities at higher exit angles.
The color shift of green radiation was 0.25 cm at an slant angle of 5 degree, and red is the control group relatively. A shift of 0.5 cm is observed at a slant angle of 15 degree, 0.75 cm at 30 degree, and 1 cm at 45 degree. At the angle of 60 degree, the dispersion could be very wide, with a broad overlapping of the primary colors. For the purpose of proofing, the yellow pixels were each counted as one red and one green pixel. At higher solid exit angles of 15 and 30 degrees, it is clearly observed that the color emission characteristics are spreading with higher values of dispersion per unit exit angle.
Since the slant angle is relatively small, the narrow dispersion in color from red radiation to green radiation could be observed patently, and blue is hardly observed. The yellow radiation could be considered as the overlap by red and green. It could be concluded that the main color light emissions are red and green with high intensities in such observed angles.
4. Modeling of the dispersion mechanisms and ray transmission
According to the already-known optical refraction and absorption phenomena using specific device structure with different dimensions developed, the emission characteristics in the Si Av LED are theoretically modeled for analyzing related wavelength dispersion phenomena. Performances of the self-developed ray tracing are analyzed using the Microsoft EXCEL tool. Since the specific wavelength of propagation and the specific propagation direction are selected in a specific position for the optical source, the refraction phenomena as they occur at each interface in the structure where a change of optical refractive index occurred are calculated. Sitting at one micron subsurface below the silicon substrate, the optical propagation mechanisms are modeled. Using the Snell’s law for refraction under the condition of the initial wave-front optical rays direction being fixed, the subsequent ray propagation directions and angles are derived as:
where n1 is the refractive index in the incident medium, n2 is the refractive index in the exit medium, θ1 is the incident angle and θ2 is the exit angle.Accordingly, the expected intensity variation along the direction of propagation is approximately given by:
where I0 is the intensity at a position from the optical source along the propagation path, and d is the distance of propagation.Refractive index values (see [36–38]) are used in the respective analyses. Progressive ray tracing was performed by successively using Eqs. (1) and (2) with EXCEL, assuming parallel wave fronts and considering change in angular propagation when interacting with each successive interface of the device. The analyses is repeated for each specific major wavelength peak as present in the Si AMLED. The initial source position was chosen as one micron below the silicon–silicon dioxide interface.
Modeling with the optical source at one micron subsurface below the silicon reveals that substantial refraction and dispersion of the propagation occurs subsurface in the silicon itself, which results in high dispersion of different wavelengths at the surface of the device (as demonstrated in Figs. 3(a)–3(c)). This principle forms the basis for the design of several of our biosensors, particularly the proposed micro-fluidic sensor as in Fig. 4, named as “CMOS BASED MICROSENSOR”.
Fig. 3. Modeling and ray tracing of the optical refraction phenomena (a) while optical source positioning at 1µm below the silicon and silicon oxide interface. Light propagates into oxide layer from emission point in silicon layer, then travels through nitride layer with little dispersion. The exit angles to the normal of the surface could be recognized. Refractive indices and refraction phenomena are proposed to occur as shown in (b) and (c).
Fig. 4. Basic scheme of fluid particles detection & analysis on a single chip by the usual route and by the use of miniaturized light emitters in which the standard CMOS technology is used.
This device consists of a micro-fluidic channel with fluid particles flowing from direction left to right, as shown in Fig. 4. At the bottom of the device is a recessed cavity with a module containing an optical source with both directional and disperse directional emission. At the top of the device is another flip chip with an array of several detector modules arranged at the lower surface of the chip. These detector modules are arranges such that the vertical emission arrays can be utilized to obtain information about the absorption characteristics of the diffusing species at the higher (650 nm) wavelength, while subsequent array sensors can detect information about specific absorbance at specific wavelengths (λ1, λ2, λ3…λn). The chip is designed such that adjacent driving and signal processing circuitry are integrated on the same chip, fully compatible with the mainstream of the standard silicon CMOS integrated circuit technology, as shown in Fig. 4.
5. Discussion and prospective
An analysis of the results reveals numerous potential applications for the derived technology in futuristic on-chip optoelectronics. These may range from (1) the placement of specifically designed optical sources with specific directional and dispersive emission characteristics; (2) the design and placement of micro wavelength dispersive coupling into micro-dimensioned on-chip optical waveguides; (3) the design and placement of broadband wavelength emitters for diverse on-chip electro-optic applications; (4) cavity-based interferometers transforming broadband wavelength emissions into narrow band on-chip optical emitters; and (5) the realization of various on-chip micro sensors that can detect a variety of parameters, ranging from standard physical parameters to a range of derived bio-parameters through the use of waveguide optics and intermediate evanescent-based waveguide-based receptor layers.
5.1 Microfluidic channel applications
The formation of violet-light-emitting devices based on silicon and their use in rapid fluorescent bio-analysis have been outlined. The fabrication process involves steps that are routinely used in current silicon device technology. The results obtained through this work have laid the basis for the development of novel and inexpensive miniaturized arrays of all-silicon light emitters that are particularly suited for fast point-of-care diagnostic applications in hand-held devices. Optical biosensors could be fabricated in various structures. For further fabrication of the schematically presented structure in Fig. 4, the each layer presence for the micro-fluidic channel biosensor is given by Figs. 5(a) and 5(b).
Fig. 5. Proposed Si Av LED with dispersion characteristics in a micro dimension biosensor. This design could integrate light source and detectors with other circuits on chip by using silicon material. (a) Lateral cross-section of the biosensor device. (b) Layer schematic of this micro-fluidic channel biosensor.
Previously mentioned Si Av LED with the specifically designed p+nn+ graded junction could be fabricated on the silicon layer, serving as light source. The light emitting point should be at about 1 µm away from the interface of Si/SiO2 layer. The detector modules direct above the light emitting point is able to measure optical absorption characteristics of the flowing through analytes if the detector array is enough sensitive to subtle changes of light intensities. Due to the incident angles and exit angles are with the degree of zero or almost zero, the dispersion phenomena is unavailable. On the other hand, if the distance between the detector array and the emitting point is the shortest, the optical intensity received will be reach the highest value. Since fluid analytes are flowing through the channel, sensors could captured the characteristics occurring by optical absorptions. Accordingly, information received from these sensors could be treated as one of the most important factor to distinguish some particularly useful information obtained from analytes.
In Fig. 6 it is noticed that, for dispersion features, the three main wavelengths of light emission have different exiting angles even if the incident angle is same, incurring by different wavelength of the optic ray having different refraction index in the Si layer. Thus a set of detector modules is used to receive optical signals with different wavelength at some specific positions. Assuming one beam of light emits from the light source, with the incident angle of 10 degree to the normal condition of inputting on the interface of Si/SiO2 layer, dispersing into three beams, and the three beams exactly hit the corresponding detecting sensors. Through the calculation of exit angles, sensors receiving dispersed wavelength light could be located exactly at the position where the exiting light hits at. The optical intensities without analytes could then be solved, as shown in Fig. 6.
Fig. 6. Calculated exit angles values for incident angle of 5 degree, 10 degree, 15 degree while the optical source is positioned at 1µm below the Si/SiO2 surface. θ1 is the incident angle to the Si/SiO2 interface and θ2 is the refraction angle in the SiO2 layer.
5.2 Optical waveguide applications
Light could be guided via an optical waveguide due to the refractive index differences in the core and the cladding medium, and the refractive index of the core is relatively higher. In the structure shown in Fig. 7, an evanescent optical field, which decays exponentially from the interface, could be generated by means of the total reflection occurring at the core-cladding interface. The target molecules in the cavity could effect refraction index result in decreasing the propagation of light in the waveguide. It is quite feasible to analyze target bio-molecules through particular sensors with a method of using qualified waveguide to detect the distinctions of the coupling and/or light propagation.
Fig. 7. Schematic of optical biosensors based on evanescent wave interaction. While the light travels through the waveguide, partial light interacts with the analytes within the cavity. The variation in the effective refractive index changes the propagation characteristics of light.
A further study is made to simulate the evanescent waves couple with analytes in the cavity etched in the nitride layer by using the RSoft Beam Prop software [39]. One multimode light gets through the high refractive index bridge waveguide, as well as the evanescent waves could pass through the cavity, interacting with analytes in the cavity, as shown in Fig. 8(a). Analytes could be some kinds of solution dissolved bio-molecules, gasses or volatile organic compounds. The interactions is mainly a function of specific refraction index, while the analytes would absorb some propagating light emissions. After interacting with analytes, the varied signals detected by sensors could become a kind of unique features to distinguish analytes. The outcomes of simulation in Fig. 8(b) shows that most optical power could be contained in the bridge-like waveguide. In the first iteration, few power losses close to the detector is observed. In subsequent iterations, this will be refined and optimized to minimize any losses and to keep all the power within the waveguide.
Fig. 8. Bridge waveguide design realized by RSoft BeamProp optical simulation software: (a) proposed design of bridge waveguide device; (b) outcome of the simulation run for the bridge waveguide design.
In Fig. 9(a), a similar RSoft BeamProp design of the device is presented, but this time with a straight SiO2 waveguide that is couples to the bio interaction receptor cavity. In this case, we designed the waveguide so that about a third of the wave propagating through the waveguide actually travels outside the waveguide as evanescent wave. This evanescent wave interacts with the target analytes (bio species) in the cavity and produce modulating refractive indices based on the optical properties of bio species locked in the receptor cavity. The simulation run in Fig. 9(b) clearly shows the evanescent wave interacted with the species in the cavity, with quite a high split in the propagation beam that couples with the species in the cavity region. In this case, the expected sensitivity of the envisaged sensor could indeed reach monolayer status.
Fig. 9. Straight waveguide design realized by RSoft BeamProp optical simulation software: (a) proposed design of straight waveguide device; (b) outcome of the simulation run for the straight waveguide design.
6. Conclusion
The combination of optoelectronic components on the same bulk silicon substrate in a single chip leads to massive advantages compared to conventional microelectronic technologies. The design of an optical sensor system requires the integration of several devices e.g. a light source and waveguide. In this paper we have presented our first step towards a Si-based integrated micro-photonic system by developing a Si-based waveguide as an effective optical interconnect for potential coupling to the Si Av LED. The specific sensor based on optical waveguide utilizes the evanescent wave to interact with analytes. By detecting related coupling and propagating properties, features of target analytes could be distinguished with high sensitivity. All the used processes are standard for microelectronics industry, which. These micro- and nano- sensors can be integrated with adjacent driving and optical processing circuits, allowing miniaturization and large-scale production using standard Si integrated circuit manufacturing processes, providing CMOS-compatible optical sensors.
Funding
National Natural Science Foundation of China (61674001, 61704019); Science and Technology on Analog Integrated Circuits Laboratory (614280205030517); National Research Foundation, South Africa (106-2221-E-006-099-MY2); Key International Collaboration, South Africa (KSC 69798).
Acknowledgments
This work was financially supported by the Natural Science Foundation of China under Contract 61704019 and 61674001, the Science and Technology on Analog Integrated Circuits Laboratory under Contract 614280205030517, the National Research Foundation Rated Researcher Incentive Funding of South Africa under Contract IFR2011033100025, and in part by a Key International Collaboration under Contract KSC 69798.
References
1. V. N. Konopsky and E. V. Alieva, “Imaging biosensor based on planar optical waveguide,” Opt. Laser Technol. 115, 171–175 (2019). [CrossRef]
2. L. M. Lehuga, “Optical biosensors,” in Biosensors and modern Biospecific Analytical Techniques, L. Gorton, ed. (Elsevier Science BV, 2005).
3. N. Khansili, G. Rattu, and P. M. Krishna, “Label-free optical biosensors for food and biological sensor applications,” Sens. Actuators, B 265, 35–49 (2018). [CrossRef]
4. M. Turemis, S. Silletti, G. Pezzotti, J. Sanchís, M. Farré, and M. T. Giardi, “Optical biosensor based on the microalga-paramecium symbiosis for improved marine monitoring,” Sens. Actuators, B 270, 424–432 (2018). [CrossRef]
5. S. Barriasa, J. R. Fernandes, J. E. Eiras-Dias, J. Brazão, and P. Martins-Lopes, “Label free DNA-based optical biosensor as a potential system for wine authenticity,” Food Chem. 270, 299–304 (2019). [CrossRef]
6. S. M. Yoo and S. Y. Lee, “Optical Biosensors for the Detection of Pathogenic Microorganisms,” Trends Biotechnol. 34(1), 7–25 (2016). [CrossRef]
7. M. F. Santangelo, E. L. Sciuto, A. C. Busacca, S. Petralia, S. Conoci, and S. Libertino, “SiPM as miniaturised optical biosensor for DNA-microarray applications,” Sens. Biosensing Res. 6, 95–98 (2015). [CrossRef]
8. D. A. Edwards, R. M. Evans, and W. B. Li, “Measuring kinetic rate constants of multiple-component reactions with optical biosensors,” Anal. Biochem. 533, 41–47 (2017). [CrossRef]
9. T. Ramon-Marquez, A. L. Medina-Castillo, A. Fernandez-Gutierrez, and J. F. Fernandez-Sanchez, “Evaluation of two sterically directed attachments of biomolecules on a coaxial nanofibre membrane to improve the development of optical biosensors,” Talanta 187, 83–90 (2018). [CrossRef]
10. R. Yan, N. Scott Lynn, L. C. Kingry, Z. Yi, T. Erickson, R. A. Slayden, D. S. Dandy, and K. L. Lear, “Detection of virus-like nanoparticles via scattering using a chip-scale optical biosensor,” Appl. Phys. Lett. 101(16), 161111 (2012). [CrossRef]
11. V. Solis-Tinoco, S. Marquez, T. Quesada-Lopez, F. Villarroya, A. Homs-Corbera, and L. M. Lechuga, “Building of a flexible microfluidic plasmo-nanomechanical biosensor for live cell analysis,” Sens. Actuators, B 291, 48–57 (2019). [CrossRef]
12. S. Sahua, J. Ali, P. P. Yupapinc, and G. Singh, “Optical biosensor based on a cladding modulated grating waveguide,” Optik 166, 103–109 (2018). [CrossRef]
13. Z. Liao, Y. Zhang, Y. Li, Y. Miao, S. Gao, F. Lin, Y. Deng, and L. Geng, “Microfluidic chip coupled with optical biosensors for simultaneous detection of multiple analytes: A review,” Biosens. Bioelectron. 126, 697–706 (2019). [CrossRef]
14. R. Newman, “Visible light from a silicon p-n junction,” Phys. Rev. 100(2), 700–703 (1955). [CrossRef]
15. W. G. Ghynoweth and K. G. McKay, “Photon emission from avalanche breakdown in silicon,” Phys. Rev. 102(2), 369–376 (1956). [CrossRef]
16. K. Xu, L. W. Snyman, J. Polleux, H. Chen, and G. Li, “Silicon light-emitting device with application in the micro-opto-electro-mechanical systems,” Int. J. Mater., Mech. Manuf. 3(4), 282–286 (2015). [CrossRef]
17. K. Xu, K. A. Ogudo, J.-L. Polleux, C. Viana, Z. Ma, Z. Li, Q. Yu, G. Li, and L. W. Snyman, “Light-emitting devices in Si CMOS and RF bipolar integrated circuits,” Leukos 12(4), 203–212 (2016). [CrossRef]
18. S. Dutta, P. G. Steeneken, V. Agarwal, J. Schmitz, A. J. Annema, and R. J. E. Hueting, “The avalanche-mode superjunction LED,” IEEE Trans. Electron Devices 64(4), 1612–1618 (2017). [CrossRef]
19. S. Dutta, R. J. E. Hueting, A. Annema, L. Qi, L. K. Nanver, and J. Schmitz, “Opto-electronic modelling of light emission from avalanche-mode silicon p+n junctions,” J. Appl. Phys. 118(11), 114506 (2015). [CrossRef]
20. G. Piccolo, P. I. Kuindersma, L-A. Ragnarsson, R. J. E. Hueting, N. Collaert, and J. Schmitz, “Silicon LEDs in FinFET technology,” in Proc. of the 44th European Solid State Device Research Conf. (ESSDERC, 2014), pp. 274–277.
21. A. Chatterjee, B. Bhuva, and R. Schrimpf, “High-speed light modulation in avalanche breakdown mode for Si diodes,” IEEE Electron Device Lett. 25(9), 628–630 (2004). [CrossRef]
22. K. A. Ogudo, L. W. Snyman, J.-L. Polleux, C. Viana, Z. Tegegne, and D. Schmieder, “Towards 10-40 GHz on-chip micro-optical links with all integrated Si Av LED optical sources, Si N based waveguides and Si-Ge detector technology,” Proc. SPIE 8991, 899108 (2014). [CrossRef]
23. L. W. Snyman, K. Xu, J.-L. Polleux, K. A. Ogudo, and C. Viana, “Higher intensity Si Av LEDs in an RF bipolar process through carrier energy and carrier momentum engineering,” IEEE J. Quantum Electron. 51(7), 1–10 (2015). [CrossRef]
24. L. W. Snyman, J.-L. Polleux, M. Plessis, and K. A. Ogudo, “Stimulating 600–650 nm wavelength optical emission in monolithically integrated silicon LEDs through controlled injection-avalanche and carrier density balancing technology,” IEEE J. Quantum Electron. 53(5), 1–9 (2017). [CrossRef]
25. J. Bude, N. Sano, and A. Yoshii, “Hot carrier luminescence in silicon,” Phys. Rev. B 45(11), 5848–5856 (1992). [CrossRef]
26. N. Akil, V. E. Houtsma, P. LeMinh, J. Holleman, V. Zieren, D. de Mooij, P. H. Woerlee, A. van den Berg, and H. Wallinga, “Modelling of light-emission spectra measured on silicon nanometer-scale diode antifuses,” J. Appl. Phys. 88(4), 1916–1922 (2000). [CrossRef]
27. J. L. Moll and R. van Overstraeten, “Charge multiplication in silicon p-n junctions,” Solid-State Electron. 6(2), 147–157 (1963). [CrossRef]
28. J. Kramer, P. Seltz, E. F. Stelgmeler, H. Auderset, B. Delley, and H. Baltes, “Light-emitting devices in industrial CMOS technology,” Sens. Actuators, A 37-38, 527–533 (1993). [CrossRef]
29. L. W. Snyman, M. du Plessis, E. Seevinck, and H. Aharoni, “An efficient, low voltage, high frequency silicon CMOS light-emitting device and electro-optical interface,” IEEE Electron Device Lett. 20(12), 614–617 (1999). [CrossRef]
30. L. W. Snyman, H. Aharoni, M. du Plessis, J. F. K. Marais, D. V. Niekerk, and A. Biber, “Planar light-emitting electro-optical interfaces in standard silicon complementary metal oxide semiconductor integrated circuitry,” Opt. Eng. 41(12), 3230–3240 (2002). [CrossRef]
31. S. J. M. Matjila and L. W. Snyman, “Increased electroluminescence from a two-junction Si n+pn CMOS structure,” Proc. SPIE 4293, 140–146 (2001). [CrossRef]
32. L. W. Snyman, M. du Plessis, and H. Aharoni, “Injection-based Si CMOS LEDs (450-750 nm) with two order increase in light emission intensity—applications for next-generation silicon-based optoelectronics,” Jpn. J. Appl. Phys. 46(4B), 2474–2480 (2007). [CrossRef]
33. M. du Plessis, H. Aharoni, and L. W. Snyman, “A silicon trans-conductance light emitting device (TRANSLED),” Sens. Actuators, A 80(3), 242–248 (2000). [CrossRef]
34. Optical Spectrum Analyzer MS9740B Brochure-Anritsu, https://dl.cdn-anritsu.com/en-en/test-measurement/files/Brochures-Datasheets-Catalogs/Brochure/ms9740b-e1101.pdf
35. M. du Plessis, P. Johannes, and E. Bellotti, “Spectral characteristics of hot electron electroluminescence in silicon avalanching junctions,” IEEE J. Quantum Electron. 49(7), 570–577 (2013). [CrossRef]
36. “Refractive Index Database,” https://www.filmetrics.com/refractive-index-database/Silicon-oxide (28 February 2018).
37. “Refractive Index of Silicon,” https://www.filmetrics.com/refractive-index-database/Si/Silicon (28 February 2018).
38. D. E. Aspnes and J. B. Theeten, “Spectroscopic analysis of the interface between Si and its thermally grown oxide,” J. Electrochem. Soc. 127(6), 1359–1365 (1980). [CrossRef]
39. RSoft Design Group, Inc., “Beam PROP 5.1.1”
