Fast photo-carrier multiplication by engineered potential trap in MoS2/Ge double junction phototransistor

Broadband photodetectors in the visible and short-wave infrared wavelengths have garnered significant interest in recent years as a desirable method to achieve better detection in adverse weather conditions. Many material combinations have been proposed to replace expensive III-V based photodetectors; however, the photodetection performance of these novel material and device concepts showed undesirable performances due to uncontrollable charge-trap-based photomultiplication, preventing fast photoresponse and gain. To solve this issue, we devised an engineered potential trap in Ge/MoS2 double junction phototransistor which show a high responsivity of 7.6 A/W (corresponding to an external quantum efficiency of 2,024%) as well as a fast photoresponse of 88.1 µs. The maximum photocurrent gain reaches 29.1 with broadband imaging capability. This excellent performance is achieved through photogenerated hole confined in p-Ge clad by MoS2 and n-Ge induced multiple electrons, which diminished rapidly via recombination upon removal of illumination. Our device concept enables creation of highly sensitive fast broadband imaging based on mixed dimensional van der Waals heterojunctions.