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 550°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.

We present results of photoluminescence and cathodoluminescence measurements of strained undoped Ino.l~Ga0.ssAs/GaAs and InolsGao.ssAs/Alol~Gao_ssAs quantum well structures, designed to throw light on the current controversy over light-hole band alignment at low In content. We compare these data with theoretical calculations of the confined state energies within the eight band effective mass approximation. Our analysis shows that for In0.1sGa 0 ssAs/GaAs, the observed two transitions are consistent with either type I or type II alignment of the light hole band for band offset ratios within the accepted range. In the case of Ino.lsGa o ssAs/Alo.15Ga o ssAs, however, our results clearly indicate type II alignment for the light hole band. We derive the band offset ratio Q, defined here as Q = AEJAE where AE c is the conduction band offset and AE~ is the bandgap difference between the quantum well and the barrier in the presdnce of strain, for the Ino.15Gao.ssAs/A10.~sGao.ssAs system to be Q = 0.83 and discuss it in the context of the common anion rule.

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