Design of Si1-xSnx alloy-based split-gate MOS field-effect phototransistors for infrared applications

This work proposes and investigates novel Si_1-xSn_x alloy-based p-channel split-gate metal-oxide-semiconductor field-effect phototransistors (p-MOSFEPT) designed for near-infrared (NIR) applications. The proposed device is grown epitaxially on the silicon (Si) platform. We utilize Si_1-xSn_x with x = 3.6% as a Virtual Substrate (VS) to minimize the lattice mismatch between the Si_1-xSn_x active layer with x = 30% and the Si substrate. The higher absorption coefficient of the Si_1-xSn_x active layer leads to improved photoresponse. Furthermore, the implementation of a periodical split-gate structure facilitates the generation and exposure of the channel on the shallow surface, enhancing the efficiency of incident light transmission and absorption, attributed to the Surface Plasmon Resonance (SPR) effect. In this work, the Finite-Element Method (FEM) is employed to analyze the electrical and optical response of the device. The results indicate that the designed device demonstrates the ability to reduce the dark current by 12.5% in comparison to conventional MOSFEPTs. Moreover, the device demonstrates remarkable photoresponse (responsivity, R = ~6×106 A/W) at 850 nm when exposed to an illuminated power of 50 nW. The value obtained represents the highest responsivity when compared to all previously available values. Consequently, there is a strong belief that the proposed phototransistor will find extensive application in NIR bands.