Density of States of a-InGaZnO From Temperature-Dependent Field-Effect Studies

Temperature-dependent field-effect measurements were performed on radio-frequency sputtered amorphous In-Ga-Zn-O thin film transistors (TFTs). We studied the effect of temperature on the TFT electrical properties. We observed that the field-effect mobility (mu) increases and the threshold voltage (V-T) shifts negatively with temperature, while the current on-off ratio and subthreshold slope (S) remain almost unchanged. We also observed that the TFT drain current (I-D) is thermally activated, and the relation between the prefactor (I-DO) and activation energy (E-a) obeys the Meyer-Neldel rule. The density of localized gap states (DOS) was then calculated by using a self-consistent method based on the experimentally obtained E-a. The result shows good agreement with the DOS distribution calculated from SPICE simulations.