Plasma and Etch Process Modulation of Subgap Trap State Density in a-Ingaznox Thin-Film Transistors

Abstract

Amorphous oxide semiconductors such as amorphous InGaZnOx (a-IGZO) possess a high concentration of subgap electronic trap states that control the performance of thin-film transistors (TFTs). Using an ultrabroadband spectroscopic method capable of directly resolving the subgap density of states, we report the effects of different etch processing and plasma treatments on the subgap. Back channel etch a-IGZO TFTs are shown to possess an acceptor-like zinc vacancy state centered at ~2.2 eV below the conduction band mobility edge, which is not present in top gate a-IGZO TFTs. We also explore how different active channel compositions and thermal annealing-activated hydrogen incorporation impact the subgap density of states of amorphous oxide semiconductors. Hydrogen is found to behave as a donor in both a-IGZO and a-ITGZO, forming a complex with valence band oxygen states after donating its electron due to its negative-U character in amorphous oxide semiconductors. Figure 1