Achievable Performance of Uncooled Homojunction GeSn Mid-Infrared Photodetectors

Abstract

Ge <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1-x</sub> Sn <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> photodetectors (PDs) have emerged as a new type of mid-infrared (MIR) CMOS-compatible PDs for a wide range of applications. Here we present a comprehensive theoretical study to evaluate the achievable performance of Ge <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1-x</sub> Sn <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> p-i-n homojunction PDs with strain-free and defect-free Ge <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1-x</sub> Sn <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> active layer for the purpose of demonstrating its potential in advancing the MIR detection technology. Starting from the Sn-composition-dependent band structures, the theoretical model calculates optical absorption, responsivity, dark current density, and detectivity. The results show that the optical responsivity can be enhanced with the Sn incorporation due to the improved optical absorption and the large mobilities and diffusion lengths of the photo-generated electrons and holes. The dark current density, however, increases with the increasing Sn composition. Our model suggests that not only the photodetection range of the Ge <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1-x</sub> Sn <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> PDs can be extended to the MIR region but their detectivity at room temperature can be competitive with the existing MIR technology, and in some cases better than some commercial PDs operating at lower temperatures. This study establishes the ultimate performance that can be potentially achieved with the Ge <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1-x</sub> Sn <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> MIR technology with the maturity of its material development in due time in addition to its much anticipated CMOS-compatible advantages.