Structural Dynamics in Amorphous Oxide Semiconductors and Its Role on Defect Formation and Transport

Amorphous oxide semiconductors (AOS) possess many unique properties, including high carrier mobility (>>a-Si:H) and optical transparency, making them attractive materials for a wide range of optoelectronic applications. Unlike Si-based semiconductors or silica glasses, AOS exhibit strong distortions in local polyhedral structure due to weaker Metal-Oxygen bonds that are ionic in nature. These distortions have been shown to cause strong electron localization near the valence and conduction band edges and deep inside the band gap when oxygen content, known to dope the oxide materials n-type, is varied. Moreover, due to the large number of degrees of freedom in AOS, thermal or photo activation may switch bond configurations out of shallow states into deep bound states or vice versa, making a static characterization inadequate for AOS. In this work, ab-initio molecular dynamics simulations are combined with accurate density-functional calculations to study time- and temperature-dependent characteristics of defects with different formation energies and degree of localization in amorphous InOx . The microscopic understanding of the structural dynamics highlights the complex nature of AOS and helps explain the observed non-equilibrium conductivity in the materials under illumination.