Investigation of the optical, electrical, and elemental properties upon annealing of spatial atomic layer deposited (SALD) Al-doped ZnO thin films

Abstract

Al-doped ZnO (AZO) has received significant attention due to its inherent properties like wide bandgap, high optical transparency, and electrical conductivity that has established its potential application in optoelectronic devices. The primary challenge in the efficient use of AZO thin films is the un-intentional formation of intrinsic defects, which deteriorate the device performance. The research community has made a significant effort to minimize these intrinsic defects and obtained high-quality films using low-cost growth techniques followed by a post-growth annealing treatment that has successfully suppressed defect states' formation. This presentation provides a comprehensive picture of the current state of knowledge on AZO's growth using spatial atomic layer deposition (SALD), comparing it with other growth methods such as ALD and physical vapor deposition. In this report, a series of AZO thin films were prepared by SALD on a glass substrate, followed by post-growth annealing from 400-550 °C, and the optical, structural, and electrical qualities of the formed thin films were evaluated using various techniques. X-ray (002) peak reveals the formation of stoichiometric films with increasing annealing temperature. UV-Vis results exhibited a marginal decrease in the bandgap until 500 °C that can be attributed to the suppression of oxygen vacancies. The refractive index monotonically increases with annealing temperatures, which correlates with the formation of higher film density due to the increase in grain size demonstrated in atomic force microscopy results. We find that the systematic variation of annealing temperature from 300–500 °C increases the film resistivity, implying a monotonic decrease in carrier concentration that matches X-ray and UV-Vis results.