Material properties and characteristics of polysilicon transistors for large area electronics

The recent progress in material, device and theoretical analysis of polysilicon transistors are reviewed. New methods for the determination of the material density of states are discussed. Based on these results a new model for the characteristics of polysilicon TFTs is deduced, which leads to an analytical expression for the threshold voltage, the subthreshold and the above threshold regime. TEM analysis has been used to correlated the electrical results with the structural properties of the films and is found in very good agreement with the experiment. We show that the material prepared under the standard conditions normally used in commercial low-pressure reactors contains a high density of defects and results in transistors with poor characteristics. A marked improvement is obtained with the deposition of films at much lower pressures. The role of different types of defects is discussed.