Abstract

This paper proposes a new nBn photodetector (nBn-PD) based on InAsSb with a barrier doping engineering technique [core–shell doped barrier (CSD-B) nBn-PD] for utilization as a low-power receiver in satellite optical wireless communication (Sat-OWC) systems. In the proposed structure, the absorber layer is selected from an ${\rm{InA}}{{\rm{s}}_{1 - x}}{\rm{S}}{{\rm{b}}_x}$ (${{x}} = {0.17}$) ternary compound semiconductor. The difference between this structure and other nBn structures is the placement of the top and bottom contacts in the form of a PN junction, which increases the efficiency of the proposed device through the creation of a built-in electric field. Also, a barrier layer is placed from the AlSb binary compound. The presence of the CSD-B layer with the high conduction band offset and very low valence band offset improves the performance of the proposed device compared to conventional PN and avalanche photodiode detectors. By applying ${-}{0.1}\;{\rm{V}}$ bias at 125 K, the dark current is demonstrated at ${4.31} \times {{1}}{{{0}}^{- 5\:}}{\rm{A}}/{\rm{cm}}^2$ by assuming high-level traps and defect conditions. Examining the figure of merit parameters under back-side illumination with a 50% cutoff wavelength of 4.6 µm shows that at 150 K, the responsivity of the CSD-B nBn-PD device reaches about 1.8 A/W under ${0.05}\;{\rm{W/c}}{{\rm{m}}^2}$ light intensity. Regarding the great importance of using low-noise receivers in Sat-OWC systems, the results indicate that the noise, noise equivalent power, and noise equivalent irradiance are calculated as ${9.98} \times {{1}}{{{0}}^{- 15\:}}{\rm{AH}}{{\rm{z}}^{- 1/2}}$, ${9.21} \times {{1}}{{{0}}^{- 15\:}}{\rm{WH}}{{\rm{z}}^{1/2}}$, and ${1.02} \times {{1}}{{{0}}^{- 9\:}}{\rm{W}}/{\rm{cm}}^2$, respectively, at ${-}{0.5}\;{\rm{V}}$ bias voltage and 4 µm laser illumination with the influence of shot–thermal noise. Also, ${{{D}}^*}$ obtains ${3.26} \times {{1}}{{{0}}^{11}}\;{\rm{cmH}}{{\rm{z}}^{1/2}}/{\rm{W}}$ without using the anti-reflection coating layer. In addition, since the bit error rate (BER) plays an essential role in the Sat-OWC systems, the effect of different modulations on the BER sensitivity of the proposed receiver is investigated. The results represent that the pulse position modulation and return zero on-off keying modulations create the lowest BER. Attenuation is also investigated as a factor that significantly affects BER sensitivity. The results clearly express that the proposed detector provides the knowledge to achieve a high-quality Sat-OWC system.

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