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

Germanium tin (GeSn) holds great potential for the development of monolithic short-wave infrared (SWIR) photodetectors. However, the large dark current and insufficient responsivity, resulting from the dense surface states and deteriorated crystal quality of high-Sn fraction GeSn thin films, pose significant challenges for their practical application. Herein, a fully strained GeSn-Ge multiple-quantum-well (MQW) bipolar heterojunction phototransistor (HPT) with an n-MoSe 2 /p-Ge van der Waals (vdW) heterostructure serving as the emitter-base junction is proposed to suppress dark current and enhance responsivity in the SWIR band. The fully strained GeSn-Ge MQWs are strategically employed as the absorption region, thereby extending the response wavelength up to 2000 nm and significantly reducing the dark current density. The developed HPT with a floating base achieves a low dark current density of 7.87 mA cm −2 at 2 V and a commendable responsivity of 1.3 A W −1 at 1550 nm along with rapid rise/fall times of 81.3 μ s/73.1 μ s. Furthermore, the phototransistor operates in self-powered mode, showcasing a high specific detectivity of 2.6 × 10 10 Jones. These results suggest that the proposed GeSn-Ge MQW-based mix-dimensional vdW HPT can effectively suppress dark current and enhance detectivity for advanced SWIR imaging applications.