Enhanced photoresponse of Ge/Si nanostructures by combining amorphous silicon deposition and annealing

Abstract

In order to inhibit high carrier recombination rates in Ge-on-Si nanostructures, GexSi1–x nanoislands were covered by a thin amorphous silicon layer via a low pressure CVD process. It is demonstrated that the surface photovoltage (SPV) signal in capped GexSi1–x/Si is increased by an order of magnitude compared to that of bare GexSi1–x islands, which can be due to the effective passivation of recombination centers at the a-Si/GexSi1–x interface. The effect is even more enhanced after subsequent annealing at 400 °C in an O2 ambient environment, with the signal increases ranging from 5 to 10 times. The observed increased photovoltage is accompanied by longer time decays in the SPV transients, being most increased after the annealing step. These results show that the photoexcited electron-hole pairs can be efficiently separated by the internal electric field at the a-Si/GexSi1–x/c-Si interfaces and can contribute to the photovoltage with decreasing recombination in GexSi1–x islands or at the interfaces. This work can facilitate the photovoltaic applications of Ge/Si heterostructures.