The increasing demand for photodetection with high capacity and low noise for long-haul optical networks has prompted researchers to develop even better heterojunction-based photodetectors. Traditional phototransistors can not meet the strict performance criteria that modern dense wavelength division multiplexing (DWDM) systems impose. This paper presents the design and full performance analysis of a Ge₁₋ₓSnₓ/Ge multiple quantum well (MQW) heterojunction phototransistor for high-speed optical communication, integrating three periods of Ge₀.₈₃Sn₀.₁₇ quantum wells surrounded by Ge₀.₈₇Sn₀.₁₃ barriers, all designed with doping profiles that enhance carrier confinement, responsivity, and gain, while maintaining low dark current. The phototransistor was modeled and simulated using COMSOL Multiphysics TCAD tools to analyze electric field distribution, carrier transport, and doping effects in the Ge₁₋ₓSnₓ/Ge multiple quantum well heterojunction. For the purpose of evaluating the applicability at the system level, the phototransistor was implemented in a 16 × 100 Gbps DWDM system using dual-polarization quadrature phase-shift keying (DP-QPSK) modulation at an aggregate data rate of 1.6 Tbps over a 2000 km fiber link with 50-GHz channel spacing. System performance was evaluated using optical simulations to quantify system performance metrics, including bit error rate (BER), signal-to-noise ratio (SNR), and quality of eye diagrams. Systems using the proposed MQW device showed significant advantages compared to those employing either Ge-on-Si or InGaAs/InP phototransistors, achieving responsivity greater than 6 A/W, bandwidth > 35 GHz, and SNR > 77 dB at 10 GHz. The results demonstrate the great potential of GeSn/Ge MQW heterostructures that extends beyond high-performance photodetector platforms, to include complementary metal–oxide semiconductor (CMOS)-compatible devices that can be used for next-generation long-reach DWDM receiver and integrated photonic circuits.
Kumar et al. (Sat,) studied this question.