High-k dielectric interlayered ITO/germanium Schottky photodiodes with low dark current and high photoconductive gain

We propose a simple germanium Schottky photodiode, in which an ultrathin Al2O3 or HfO2 interlayer is inserted between the indium-doped tin oxide (ITO) and n-Ge contact, showing low dark current and ultra-high responsivity (gain). The introduction of 2 nm thick Al2O3 interlayer in a ITO/n-Ge Schottky photodetector results in 138 × reduction of dark current, and 16 × improvement of responsivity, exhibiting a low dark current density of 32 mA/cm2 and high responsivity of 12.5 A/W (external quantum efficiency: 1183%) for 1310 nm and 7.3 A/W (external quantum efficiency: 584%) for 1550 nm at − 4 V reverse bias, respectively. The large responsivity up to 18.5 A/W is obtained for 1310 nm at − 9 V for ITO/Al2O3(2 nm)/n-Ge diode, which corresponds to a large photoconductive gain of 24. Such a high photoconductive gain may be attributed to the capture of holes by the traps at the interface. These results are of significance for the fabrication of Ge photodetector with high performances.