Growth of Ga-doped ZnO films by thermal oxidation with gallium and their optical properties

Metal gallium was evaporated onto ZnS films by physical vapor deposition method and then the thermal oxidation in the air was subsequently performed for the growth of Ga-doped ZnO films. The microstructures, photoluminescence (PL) and optical absorption properties of the Ga-doped ZnO films prepared under different deposition and oxidation conditions were investigated. The results showed that certain Ga doping can decrease the defects level, improve the crystallinity of ZnO films, and it became more effective with the extension of oxidation time. As the oxidation time increased, the Ga-doped ZnO films became more compact and uniform, displaying higher crystallinity. In addition, the optical band gaps of the ZnO films increased, the PL intensity of the visible emission decreased, and the luminescent center of the visible emission changed. Among them, the 505 nm emission resulted from oxygen vacancy, while the 539 nm emission was associated with oxygen interstitial.