Electrically or chemically tunable photodetector with ultra high responsivity using graphene/InN nanowire based mixed...

In this work, an electrically/chemically tunable highly sensitive photodetector based on mixed dimensional heterojunction of graphene and planar InN nanowires (NW) is presented. Controlled partial oxidation of InN has been employed to effectively reduce the high surface carrier concentration of InN, which normally prevents it from forming good rectifying contact with graphene. The resulting surface modified InN NWs have been found to form excellent Schottky junction with graphene, with an increase in effective Schottky barrier height (SBH) by over 1.1 eV and a ratio of forward and reverse bias currents exceeding 4 orders of magnitude. Moreover, very strong barristor (gate tunable heterojunction) action has been observed, withI_on/I_off ≈ 4 orders of magnitude, and SBH increase by >0.3 eV. The barristor has been demonstrated to be highly sensitive to light, especially in the ultra-voilet, visible and near IR spectra. Responsivity was found to be widely tunable by gate voltage, with the highest value exceeding 1000 A W^-1. Rise and fall times being in the range of hundreds of ms are indicative of photoconductive gain, which can be attributed to the ultra high responsivity. A method of semi-permanent molecular doping has been demonstrated to realize a two-terminal version of the photodetector, where the desired responsivity can still be achieved without requiring a back gate terminal, enabling the device to be realized on insulating substrates. The effect of encapsulation has been studied as a function of time, which has showed the long term stability of the dopant-induced enhancement and ultra high responsivity of the barristor photodetector.