Tunable Schottky barrier and high responsivity in graphene/sinanotip optoelectronic device

We demonstrate tunable Schottky barrier height and record photo-responsivity inanew-concept device madeofasingle-layer CVD graphene transferred ontoamatrixofnanotips patterned onn-type Si wafer. The original layout, where nano-sized graphene/Si heterojunctions alternate to graphene areas exposed to the electric field of the Si substrate, which acts both as diode cathode and transistor gate, results in a two-terminal barristor with single-bias control of the Schottky barrier. The nanotip patterning favors light absorption, and the enhancement of the electric field at the tip apex improves photo-charge separation and enables internal gain by impact ionization. These features render the deviceaphotodetector with responsivity (3 A W^-1 for white LED lightat 3 mW cm^-2 intensity) almost anorder of magnitude higher than commercial photodiodes.We extensively characterize the voltage and the temperature dependence ofthe device parameters, and prove that the multi-junction approach does not add extra-inhomogeneity tothe Schottky barrier height distribution. We also introduceanew phenomenological graphene/semiconductor diode equation, which well describes the experimental I-V characteristics both in forward and reverse bias.