The influence of spatially non-uniform density-of-state distributions on the characteristics of a-Si: H thin-film transistors

The potential profile in the semiconductor of a thin-film transistor is calculated on the basis of model distributions for the bulk density of states in a-Si:H. In addition a spatially non-uniform defect density distribution close to the semiconductor-insulator interface and a model for the density of interface states is considered. From this potential the source-drain current of the thin-film transistor is obtained. These data are then analysed using the conventional scheme in which a homogeneous density-of-states distribution in the bulk and no interface states are assumed. The resulting effective density-of-states function reflects the nonuniformities in a characteristic way. A simple method to determine interface state distributions from experimental field-effect data is also presented and experimental data are analysed in terms of interface states and non-uniform defect distributions.