Admittance Spectroscopy of Interface States in $\hbox {ZnO/HfO}_{2}$ Thin-Film Electronics

The electronic properties of ZnO/HfO₂ interface states are studied by dc current-voltage and ac admittance spectroscopy on thin-fllm transistors (TFTs) and metal-insulator-semiconductor capacitor structures. Subthreshold behavior of the transistors indicates an interface state density (N_it) value of 7.2 × 10¹² cm^-2. Cole-Cole plots of ac admittance demonstrate Debye behavior and extracted energy-dependent inter face state density (D_it) with an approximate exponential decay of 3.0 × 10¹³ cm^-2 · eV^-1 near the conduction band to 1.2 × 10¹² cm^-2 · eV^-1 at 0.9 eV below the conduction band. The integrated interface state density from these measurements is N_it = 7.9 × 10¹² cm^-2, which is consistent with the value obtained from subthreshold behavior of the TFTs.