High performance n-MoSe2/p-Ge-GeSn MQWs/n-Ge heterojunction phototransistor for extended short-wave infrared photodetection

Abstract Germanium tin (GeSn) is promising to realize monolithic short-wave infrared (SWIR) photodetectors. However, the large dark current and insufficient responsivity resulted from high density of surface states and deteriorated crystal quality of high-Sn fraction GeSn thin films pose significant challenges for their practical application. Herein, fully strained GeSn-Ge multiple-quantum-wells (MQWs) bipolar heterojunction phototransistor (HPT) with an n-MoSe2/p-Ge van der Waals (vdW) heterostructure serving as emitter-base junction is proposed for suppressing the dark current and enhancing the responsivity in SWIR band. The fully strained GeSn-Ge MQWs are strategically employed as the absorption region to extend the response wavelength up to 2000 nm and significantly reduce dark current density. The developed HPT achieves a low dark current density of 7.87 mA/cm2 at 2 V and a commendable responsivity of 1.3 A/W at 1550 nm along with rapid rising/falling times of 81.3 μs/73.1 μs. Furthermore, the phototransistor operates in a self-powered mode, showcasing a high specific detectivity of 2.6 × 1010 Jones. These results suggest that the proposed GeSn-Ge MQWs-based mix-dimensional vdW HPT can effectively suppress dark current and enhance detectivity for advanced SWIR imaging applications.