Photo response of a-IGZO thin films as a function of annealing temperature

Abstract

This paper investigated the photo response behavior of amorphous indium gallium zinc oxide (a-IGZO) thin films, identifying three distinct photoconductivity types corresponding to different oxygen vacancy concentrations: Type I (low vacancy density), Type II (intermediate density), and Type III (high vacancy density). The results reveal that the photoconductive properties of a-IGZO are massively influenced by oxygen vacancy concentration, which can be precisely controlled through vacuum annealing. Type I films exhibit rapid recombination of photogenerated electron-hole pairs when illumination is removed, suggesting minimal involvement of defect states. Contrarily, Types II and III yield slower photo response and increasingly persistent photoconductivity, reflecting the growing presence of ionized oxygen vacancies that act as donor states. This demonstrates the essential impact of vacancy-induced defect levels on carrier trapping and recombination behavior. In films with low vacancy densities, defect generation under illumination was observable, while in films with higher vacancy concentrations, incident light ionizes oxygen vacancies, increasing donor state density and enhancing photoconductivity. Moreover, the observed photo response characteristics provide a useful indicator of film quality. The study's findings emphasize the role of oxygen vacancy in the electronic and optoelectronic properties of a-IGZO, offering practical guidance for implementing quality IGZO films.