GaN thin films deposition by laser ablation of liquid Ga target in nitrogen reactive atmosphere

GaN thin films were deposited by laser ablation of liquid Ga target in nitrogen reactive atmosphere. An Nd-YAG laser (lambda = 1.06 mu m, tau(FWHM) = 10 ns) of 0.35 J energy/pulse was used as laser source. The nitrogen pressure was varied in the range of 10(-2) to 10(-1) mbar. As substrates, we used (0001) sapphire plates and (100) Si wafers, coated or uncoated with ZnO as buffer layers, and heated below 300 degrees C. Different analysis techniques evidenced the characteristics of the deposited films. SIMS profiles corresponding to N and Ga in-depth distribution carried out the presence of layers of the order of 130-150 nm, with uniform distribution of Ga and N inside the layer. XPS studies evidenced the Ga-N bonding. The Nls signal contains as main peak the one centered at 397.3 eV and corresponding to Ga-N bond. From the distance between the photoelectron Ga 3d peak and the Auger Ga LMM peak, the calculated Auger parameter of 1083.9 eV corresponds to the one reported in literature for GaN compound (1084.05 eV). Both techniques evidenced an oxygen contamination below 5%. XRD recorded spectra show the presence of a peak assigned to (002) GaN crystalline orientation. Optical absorption spectroscopy studies in the UV-visible range evidenced a high transparency (over 80% transmission) for the deposited films. The energy band gap obtained from the absorption spectra was found to be larger than 3.6 eV. (C) 1998 Elsevier Science B.V.