Effect of Hydrogen Incorporation on Sub-Gap Density of States in Amorphous Ingazno Thin-Film Transistors

Amorphous semiconducting transparent oxides like InGaZnO4 (a-IGZO) have a broad distribution of metal and oxygen vacancy defects that determine thin film transistor (TFT) characteristics and impact device metrics such as hysteresis. Here, we demonstrate how hydrogen modifies the density of states (DoS) through a novel on-chip method that spectrally resolves trap concentration in a-IGZO spanning the bandgap. Requiring laser energies continuously tunable from 0:26 to 3:1 eV, this method also employs difference-frequency generation to access shallow states near the conduction band. We characterize the effect of hydrogen incorporation on the sub-gap peaks of the DoS of an a-IGZO TFT. Specifically, our data suggest hydrogen hybridizes with both metal and oxygen vacancy defects. These interactions result in a suppression of oxygen vacancy trap sites and a peak shift in the metal vacancy-related region in the sub-gap DoS near the valence band maximum. Temperature-dependent, photon energy-dependent hysteresis, and transient defect lifetime measurements further reveal the strong impact of hydrogen concentration on a-IGZO TFT performance germane to current optical display technology.