Surface oxide modification enables super-linear photoresponse in a single Germanium nanowire photodetector

Abstract

We report observation of a super-linear photocurrent dependence on intensity of illumination in a single Ge nanowire (NW) of diameter ~60 nm. The super-linear dependence was enabled by a controlled and short duration vacuum annealing of the prefabricated NW photodetector to 400 °C. The short annealing leads to substantial overall performance enhancement of the broad band (300 nm–1100 nm) photo-detector such as reaching a Responsivity of ~0.6 × 107 A/W and a Specific Detectivity ~1014cmHz1/2/W. A combination of low frequency (<10 Hz) 1/f noise spectroscopy as well as X-Ray Photoelectron Spectroscopy showed that reduction of sub-oxide content in the surface oxide layer of a Ge NW leads to reduction of states with slow kinetics. That in turn prompts the onset of super-linear behavior along with enhancement of photodetector figures of merit.