Ambient air effects on electrical characteristics of GaP nanowire transistors

Gallium phosphide (GaP) nanowire transistors were fabricated in back-gated structure, and their electrical characteristics were measured systematically in both air and vacuum. The transistors turn on typically between -5 and -7 V in ambient air. However, a large threshold voltage (V_th) shift, ∼10 V, toward negative gate bias was observed in vacuum. After the transistors were exposed to air for 48 h, V_th returned to the similar value in ambient air, implying a reversible process. The rate of V_th shift slows down when they were exposed to N₂ in comparison with that of air. The shift of V_th is believed to be related to the charge transfer from the surface of GaP nanowire to the physically adsorbed OH or oxygen. In addition, the observed V_th shift from the GaP nanowire transistors can be explained by the conventional n-channel depletion mode metal-oxide-semiconductor field-effect transistor.