Simulation of influence of density of states in a-Si:H on electrical performance of a-Si:H thin-film transistors

A two-dimensional analysis of the density of states in hydrogenated amorphous silicon (a-Si:H) thin film transistors (TFT) is simulated by Semicad Device program. The model of the density of states in a-Si:H consists of conduction-band and valence-band-tail states, and deep-gap states. We found that mobility is sensitive to the conduction-band-tail states and threshold voltage is mainly determined by the combination of the deep-gap states, interface states and fixed charges, which are localized at or near the gate insulator/a-Si:H interface. We have also analyzed the physical origin of the nonlinearity of current-voltage characteristic of a-Si:H TFT. The influence of top and bottom gate insulator/a-Si:H interfaces on TFT performance are compared.