Surface and optical properties of nanocrystalline GaN thin films on sapphire (0001) by pulsed laser deposition

GaN thin films have been grown on sapphire (0001) substrates by pulsed laser deposition. The thin films deposited at different substrate temperature have been evaluated by X-ray diffraction (XRD), photoluminescence spectroscopy (PL), and X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM). The influences of depositing temperature on surface and optical properties of the GaN thin films have been studied. The XRD results show that the lowest full width at half maximum (FWHM) of (0002) X-ray diffraction line of the GaN film was deposited at about 700 degrees C. The photoluminescence (PL) spectra were measured at 7 K. The quantum confinement effects of the nanocrystalline GaN films have been evaluated by the band edge PL peaks. The energy shift of the band edge PL peaks of GaN film deposited at 700 degrees C have been estimated by the effective mass approximation method. The chemical composition and the native oxide of the GaN film surface were investigated by the XPS spectra. Average roughness and surface morphology of the GaN thin films deposited on the sapphire (0001) substrates have been evaluated by AFM.