Quantitative Analysis of the Density of Trap States in Semiconductors by Electrical Transport Measurements on Low-Voltage Field-Effect Transistors

A method for extracting the density and energetic distribution of the trap states in the semiconductor of a field-effect transistor from its measured transfer characteristics is investigated. The method is based on an established extraction scheme [M. Grunewald et al., Phys. Stat. Sol. B 100, K139 (1980)] and extends it to low-voltage thin-film transistors (TFTs). In order to demonstrate the significance of this extension, two types of TFTs are fabricated and analyzed: one with a thick gate dielectric and high operating voltage and one with a thin gate dielectric and low operating voltage. From the measured transfer characteristics of both TFTs, the density of states (DOS) is calculated using both the original and the extended Grunewald method. The results not only confirm the validity of the original Grunewald method for high-voltage transistors, but also indicate the need for the extended Grunewald method for the reliable extraction of the trap DOS in transistors with a thin gate dielectric and low operating voltage.