Design and Analysis of GeSn-Based Resonant-Cavity-Enhanced Photodetectors for Optical Communication Applications

We propose and analyze GeSn resonant-cavity-enhanced photodetectors (RCE-PDs) to achieve high-speed and high-responsivity photodetection for communication applications. The designed GeSn RCE-PDs comprises a Ge/GeSn/Ge p-i-n photodiode structure grown on a silicon-on-insulator (SOI) substrate and a Si/SiO2 distributed Bragg reflector (DBR). The incorporation of Sn into the active layer effectively reduced the direct bandgap energy, thereby extending the photodetection range to longer wavelengths and, thus, enhanced the optical responsivity. The buried oxide and the Si/SiO2 DBR act as the top and bottom mirrors, respectively, that considerably enhance the responsivity. We show our theoretical models to calculate the optical absorption coefficient, bandwidth, reflectivity, and responsivity, and we optimize the proposed devices to simultaneously achieve high-responsivity and high-speed operation at 1550 nm and 2000 nm. The results show that the optimized GeSn RCE-PDs can achieve a responsivity of 0.619 A/W for 6% Sn (1.02 A/W for 10% Sn) and high 3-dB bandwidth of ~58 GHz (59 GHz) at 1550 nm (2000 nm). These results show that the proposed GeSn RCE-PDs are very promising for high-performance photodetection in communication applications.