Characterisation of microcrystalline GaN grown on quartz and on sapphire by laser and microwave plasma enhanced metalorganic chemical vapour deposition

We present a comparative study of GaN grown on quartz and on sapphire by laser assisted metalorganic chemical vapour deposition. Films were characterised by X-ray diffraction, Raman spectroscopy and optical transmission. Films grown on both substrates are polycrystalline, with the dominant orientation of (0002) wurtzite or (111) cubic for growth temperatures 55O°C and lower. In films grown at 625°C, both on quartz and on sapphire the crystallites show a variety of orientations, all attributed exclusively to wurtzite phase. Films grown at the same temperature are characterised by similar value of the Urbach parameter for both substrates. The Raman spectra in all examined films are alike, and characteristic for a disordered cubic GaN.