Defects generated by MF magnetron sputtering and their influences on the electrical and optical properties of Al doped ZnO thin films

Abstract

In this paper, the defects of Al doped ZnO films generated by magnetron sputtering in the deposition processes are comprehensively investigated. It is found that oxygen ion bombardment deteriorates the crystallinity and generates oxygen related defects, such as oxygen interstitials (Oi), chemisorbed oxygen at the grain boundaries (OGB), and oxygen vacancies (VO). Oi and OGB decrease the carrier concentration and mobility of the pristine films remarkably, but they can be removed by hydrogen annealing. However, the grain boundary scattering originated from poor crystallinity cannot be reduced by the annealing below 450°C. Moreover, the in-situ temperature-dependent resistivity measurement under hydrogen atmosphere suggests that hydrogen atoms are incorporated into the ZnO: Al films and interact with VO. We propose that there are two energetically favorable states for the incorporated hydrogen. The defect configurations of (H2)i and HO+Hi are assigned to the high resistivity state (HRS) and low resistivity state (LRS) respectively and the switching between these two states is activated by VO and mediated by a metastable state (H2)*O. The transformation between these two resistivity states leads to a hysteresis loop during the heating and cooling process.