Design of Mid-Infrared Ge1-xSnx/Ge Heterojunction Photodetectors on GeSnOI Platform with a Bandwidth Exceeding 100 GHz

This work presents normal-incidence p⁺-p-n-n⁺ Ge/Ge _1-x Sn _x (x = 6-12%) heterojunction photodetectors (PDs) on germanium-tin-on-insulator (GeSnOI) substrate for mid-infrared (MIR) application. The GeSnOI substrate facilitates the detector to achieve a low leakage current and offer efficient optical confinement. Utilizing COMSOL Multiphysics, the devices' DC and RF characteristics in both illuminated and dark conditions have been examined. Three Sn concentrations—6, 9, and 12%—have been considered here in order to investigate their effects on the functionality of the proposed device. Consequently, the optical signal up to 3.1 μm can potentially be detected by the proposed device. At T = 300 K, a dark current density of 0.027, 0.2, and 1.415 A/cm ² under −1 V bias is attained for Sn = 6, 9, and 12%, respectively. The dark current densities obtained here are lower than those reported in previous theoretical and experimental studies. For a 2-μm illumination wavelength under zero bias and Sn = 12%, an optical responsivity of 0.31 A/W is achieved. Moreover, a 3dB bandwidth ( f_3dB ) of around 100 (175) GHz is attained at 0 (-2) V, the highest recorded value among all group III–V and group IV photodetectors operating in the 2-μm wavelength region. The proposed device shows the significant potential of a GeSn PD in the MIR wavelength region.