Tunable Schottky barrier and high responsivity in graphene/Si-nanotip optoelectronic device

Abstract

We demonstrate tunable Schottky barrier height and record photo-responsivity\nin a new-concept device made of a single-layer CVD graphene transferred onto a\nmatrix of nanotips patterned on n-type Si wafer. The original layout, where\nnano-sized graphene/Si heterojunctions alternate to graphene areas exposed to\nthe electric field of the Si substrate, which acts both as diode cathode and\ntransistor gate, results in a two-terminal barristor with single-bias control\nof the Schottky barrier. The nanotip patterning favors light absorption, and\nthe enhancement of the electric field at the tip apex improves photo-charge\nseparation and enables internal gain by impact ionization. These features\nrender the device a photodetector with responsivity (3 A/W for white LED light\nat 3 mW/cm2 intensity) almost an order of magnitude higher than commercial\nphotodiodes. We extensively characterize the voltage and the temperature\ndependence of the device parameters and prove that the multi-junction approach\ndoes not add extra-inhomogeneity to the Schottky barrier height distribution.\nThis work represents a significant advance in the realization of graphene/Si\nSchottky devices for optoelectronic applications.\n