Performance of metal-semiconductor field effect transistors on mist chemical-vapor-deposition grown ZnO channels with intentionally oxidized AgOx Schottky 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.