Effects of Ga concentration and rapid thermal annealing on the structural, optoelectronic and photoluminescence properties of Ga-doped ZnO thin films

In this study, Ga-doped ZnO (GZO) thin films were grown on sapphire substrates at a low temperature of 350 °C by metalorganic chemical vapor deposition (MOCVD). The Ga content of GZO was varied by the triethylgallium (TEGa) flow rate from 0 to 20 sccm. The structural, optoelectronic and photoluminescence properties of GZO thin films were investigated in detail. Moreover, to improve these characteristics, the as-grown GZO thin films were further treated via the rapid thermal annealing (RTA) process at 550 °C for 2 min in N2 ambient. After RTA process, the crystal quality of GZO films was enhanced. From the transmittance spectra, it was found that the as-deposited and annealed GZO films both possessed high transparency above 90% with the wavelength range from 400 to 800 nm. Based on the photoluminescence results, there existed mixed bandgaps within the GZO films when the TEGa flow rate was higher than 10 sccm during the MOCVD growth. Not only, the improvement of GZO crystallinity and a blueshift in bandgap peaks also occurred. Additionally, the intensity of the bandgap to broad band luminescence peaks was increased. Furthermore, the electrical resistivity of GZO can be reduced efficiently through the RTA treatment. It reveals that the RTA process is indeed helpful to GZO thin films.