Accurate Defect Density-of-State Extraction Based on Back-Channel Surface Potential Measurement for Solution-Processed Metal-Oxide Thin-Film Transistors

We report more accurate extraction method of the defect density of states for solution-processed indium-gallium-zinc-oxide (IGZO) thin-film transistors (TFTs). Since the solution-processed IGZO TFTs have a very thin (~8 nm) active semiconductor layer, their back-channel surface potential should be considered in the field-effect method. If the back-channel surface potential is ignored, deviation between theoretically derived and experimentally measured activation energy data becomes more significant as the thickness of the semiconductor layer decreases in comparison with its Debye length. Dependence of the back-channel surface potential on the applied gate voltages was verified by scanning Kelvin probe microscopy and found to be proportional to the gate voltages. The modified field-effect method provided a more accurate model of the activation energy over the subthreshold region and correspondingly more accurate defect density of states of the IGZO TFTs.