Enhanced mechanism investigation on violet-blue emission of ZnO films by incorporating Al and Zn to form ZnO-Al-Zn films

ZnO, ZnO-Zn, ZnO-Al0.10-Zn and ZnO-Al0.15-Zn are deposited on glass substrates by radio frequency and direct current magnetron co-sputtering. Photoluminescence (PL) measurements show that the optical performances of samples are strongly dependent on both Al and Zn incoprations. The origin of the defect-related PL emission has been investigated for a long time. Several different hypotheses have been proposed, however, they are still under investigation. Especially for the blue emissions, its origins have been debated intensely for more than thirty years because of its sparsity and instability. In this paper, both violet and blue emissions are observed in all the samples. PL emission decreases sharply as Zn is doped in ZnO to form ZnO-Zn film. However, as both Al and Zn are simultaneously doped in ZnO to form ZnO-Al0.10-Zn film, PL emission conversely increases and attains the maxima. In addition, PL emission decreases again with the increase of Al target power to form ZnO-Al0.15-Zn film. We concluded that violet-blue emission is ascribed to defect types in reverse change trend with interstitial Zn, such as Zn vacancies. This is different from previous universal hypothesis that violet-blue emission is from interstitial Zn defects.