VOLTAGE-DEPENDENCE OF OFF CURRENT IN A-SI-H TFT UNDER BACKLIGHT ILLUMINATION

We have studied the off currents of a-Si:H TFT at negative gate voltag es, The voltage dependence of the off current in a-Si:H TFT is explain ed as the hole current limited by two competing components, channel co nductance due to hole accumulation and the drain junction conductance under backlight illumination, When enough carriers are injected from t he source and drain regions by photogeneration, two quite different ga te voltage dependences appeared, In the dark condition the increasing off current with negative gate bias is the hole current injected from the drain junction region, and the hole generation seems to originate from the thermally-assisted tunneling via the localized states in a-Si :H near the drain junction because of its small activation energy of 0 .1 similar to 0.2 eV.