A Two-Terminal p-GaSe/n-Ge/Au Heterojunction Phototransistor With a Schottky Barrier Collector for Extension of Short Wavelength Infrared Band

The extension of the response wavelength range of germanium (Ge) photodetector (PD) beyond 1600 nm is beneficial for its versatile applications in short wavelength infrared bands. Herein, a two-terminal p-GaSe/n-Ge/Au heterojunction phototransistor (HPT) with the Au/n-Ge Schottky barrier collector is demonstrated to extend response wavelength beyond 2000 nm due to the amplification of photocurrent generated by internal photoemission effect (IPE). The Schottky barrier height (SBH) of Au/n-Ge is about 0.51 eV, corresponding to the cutoff wavelength of 2430 nm theoretically, but usually with low quantum efficiency. The large bandgap offset of the p-GaSe/n-Ge emitter-base junction results in a high carrier injection ratio, thereby a high photocurrent gain, which strongly enlarges the photocurrent generated by hot electrons surpassing the Schottky barrier at the collector, rendering the responsivity of 7.7 A/W at 1860 nm. The peak responsivity of 42.5 A/W and high specific detectivity of 1.3 × 10<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><roman>10</roman></sup> Jones at 1550 nm for the HPT under 2 V bias voltage is achieved with high speed in terms of rising/falling times of 11.6/4.1 μs. Those results demonstrate that the Ge HPT with a Schottky barrier collector is a feasible strategy for extended short-wave infrared (SWIR) photodetection.