Performance of metal-semiconductor field effect transistors on mist chemical-vapor-deposition grown ZnO channels with intentionally oxidized AgOxSchottky contact gates

Abstract

Metal-semiconductor field-effect transistors (MESFETs) were fabricated on ZnO thin films grown via mist-chemical vapor deposition (mist-CVD), a solution-based, highly scalable, non-vacuum technique. High-performance MESFETs were achieved by using in situ intentionally oxidized AgOx Schottky contact (SC) gates with large effective barrier heights (1.13-1.18 eV) and rectification ratios (at ±2 V) of >107. The device properties of the resulting MESFETS were investigated as a function of channel thickness, gate length, and temperature (T = 25-130 °C) with the best performing devices characterized by on/off current ratios >107, channel mobilities of 5.7 cm2V-1 s-1, and sub-threshold slopes of ∼100 mV/decade at room temperature. Reliable operation was maintained up to 130 °C with only a gradual increase in off current due to increased thermionic emission across the SC gate. These results demonstrate the potential of using the combination of mist-CVD ZnO channels and AgOx SC gates to produce low-cost, low operating voltage, transparent thin film transistors. The key physical processes are a significant increase in Schottky barrier height and the passivation of oxygen vacancies at the gate-channel interface due to the presence of reactive oxygen species during the deposition of the AgOx gate.