Amorphous indium gallium zinc oxide (a-IGZO) is a transparent amorphous oxide semiconductor (TAOS) that has shown promise as transparent thin film transistors (TTFTs) in various display applications. Within a-IGZO films, states can form in the band gap that hinder TTFT performance. In order to elucidate the origin of these states, we examined the formation of the subgap states for a-IGZO thin films with various compositions. We observed a positive correlation between the subgap formation and the percentage of oxygen ruling out oxygen deficiencies as a factor in the formation of subgap states. Furthermore, metallic indium crystallites were observed to form for samples grown in oxygen deficient conditions. Our studies reveal that subgap states are due to oxygen with few surrounding metal neighbors and indium with few surrounding oxygen neighbors. The subgap states can be suppressed in a-IGZO (and other TAOS) by careful choice of composition.
Lebens-Higgins, Z., Dailey, A., & Piper, L. (2015). Orgin of Subgap Features in Transparent Amorphous Oxide Semiconductors. Alpenglow: Binghamton University Undergraduate Journal of Research and Creative Activity, 1(1). Retrieved from https://orb.binghamton.edu/alpenglowjournal/vol1/iss1/6