Effect of Defects on the Performance of Si-Based GeSn/Ge Mid-Infrared Phototransistors

Abstract

In this paper, we discuss the impact of interfaces and defects on the frequency performance of Si-based GeSn heterojunction phototransistors (HPTs) at room temperature. Furthermore, the effect of base-emitter (B-E) voltage on the spectral responsivity (SR) and detectivity (D*) has also been studied. The presented device consists 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> alloy in the active layer to enhance the photodetection range. However, increasing Sn content in 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> causes a lattice mismatch between 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> and Ge virtual substrate (VS), which may increase defect density at the heterointerfaces. As a result, the diffusion length (L <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">p</sub> ) and minority carrier lifetime (τ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">p</sub> ) may decrease, thereby, degrading the performance of the device. Three major noise components such as shot noise current components at the base-emitter (B-E) and base-collector (B-C) junctions and Johnson noise have been considered for the first time to calculate the detectivity and noise-equivalent-power (NEP) of the presented device. The calculated results show that the decrease in diffusion length does not cause a significant impact on the SR, D* and internal quantum efficiency (IQE), however, it significantly degraded the cut-off frequency (f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</sub> ), maximum frequency (f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">max</sub> ), and sensitivity (S) of the GeSn HPT at 300 K.