Effects of the rear interface states and fixed charges on the electrical characteristics of thin film transistors with thin amorphous silicon layers

The electrical characteristics of the thin film transistors (TFT's) with hydrogenated amorphous silicon (a-Si:H) films thinner than 0.1 mu m have been carefully studied to show that the interface states and fixed charges at the rear interface will play the comparable effects to those at the front interface on the field effect conductance. It is dearly demonstrated that as the thickness of the active layer is smaller than the theoretically expected width of the space charge region, the potential at the rear interface will be affected by the gate voltage. This is very different from the conventional case with a thicker active layer. Since the TFT's at present have smaller typical thicknesses of the semiconductor films than the expected width of the space charge region, the effects of the interface states and the fixed charges at both the rear and front interfaces, as well as the bulk states of the thin a-Si:H films, must be taken into account concurrently.