Effects of annealing in N2 on sputtered Al-doped ZnO thin films

Abstract

Transparent conductive oxides (TCOs) are a unique class of materials that exhibit both low electrical resistivity and high optical transmittance. Al-doped ZnO thin films have the potential to replace the widely used TCO indium tin oxide at a fraction of the current cost. Thin ZnO:Al films have been deposited by rf magnetron sputtering at room temperature onto fused quartz substrates. An ex situ anneal at 350°C in N2 was employed to improve both the electrical and optical properties of as-deposited films. The calculated average grain size increased from 25.6to28.3nm following the anneal. The resistivity was found to decrease from 3.7×10−3to7.1×10−4Ωcm as a result of postdeposition processing. An average optical transmittance of >85% was routinely observed for annealed films. X-ray photoelectron spectroscopy measurements were conducted in order to investigate the degree of oxygen deficiency of both as-deposited and annealed films. It was found that the annealing procedure generated an oxygen poor region near the film surface. The authors propose that the formation of oxygen vacancies in conjunction with improved crystalline quality is responsible for the measured improvement in film resistivity.