Influence of hydrogen annealing on structure and optoelectronic properties in Al doped ZnO thin films

Abstract

Al doped ZnO (AZO) thin films are of significant interest for flat panel displays, solar cells, etc. In this regard, AZO films were prepared in Ar atmosphere by radio frequency magnetron sputtering with an AZO (2 wt-%Al2O3) ceramic target at room temperature. To investigate the influence of hydrogen related defects on the structure and optoelectronic properties in AZO films, the prepared films were annealed in Ar+H2 ambient at different temperatures (100–500°C). The results show that the films’ crystallinity becomes better and the resistivity decreases with the increase in annealing temperature. The lowest resistivity of 2·79×10−3 Ω cm is obtained after 500°C hydrogen annealing, which decreases by about four orders of magnitude compared to the resistivity of as deposited film. The improvement of electrical properties is attributed to the formation of H related defects and desorption of weakly bonded oxygen species near grain boundaries in AZO films after H2 annealing treatment, and the corresponding physical mechanism was discussed. It is proved that hydrogen annealing is an effective method for the improvement of electrical properties in AZO thin films. The optical bandgap energy of the films obviously increases with the increase in annealing temperature due to Burstein–Moss effect.