Top-gated field-effect transistor and rectifying diode operation of core-shell structured GaP nanowire devices

We have fabricated top-gated GaP nanowire field-effect transistors using core-shell structured GaP nanowires grown by a chemical vapor deposition method. As expected, based on results of a thin Ga2O3 shell serving as a gate oxide, our top-gated GaP nanowire FETs exhibited more effective gate-channel coupling when compared to the conventional back-gated one. Above the threshold voltage of 1.5 V, diode like I-V characteristics were observed between the source and top-gate electrode. This can be explained by the formation of a midgap GaP/wide-gap Ga2O3 heterojunction. Measured current from in between the source and top gate shows extreme sensitivity toward ultraviolet illumination, which can be attributed to the electron-hole pair generation in the Ga2O3 layer. The first-principle electronic structure calculations on Ga2O3 crystal revealed a reduction in the band gap (4.8 eV -> 3.8 eV) due to the development of oxygen vacancy states in the forbidden band gap.