X-ray diffraction studies of high-quality GaN heteroepitaxialfilmsgrown by metal organic chemical vapour deposition

The authors report the growth and characterisation of high-quality GaN films grown on (0001)-oriented sapphire (Al2O3) substrates by metal organic chemical vapour deposition (MOCVD). These films were analysed using five-crystal X-ray diffraction, optical transmission spectroscopy, transmission electron microscopy (TEM) and cathodoluminescence. The X-ray diffraction FWHM value of ΔΘ ≃ 37 s-1 is the narrowest reported to date. The dependence of FWHM on epilayer thickness exhibits the classical behaviour commonly observed in more conventional III-V materials and implies an extinction depth much smaller than that which might be inferred from the X-ray diffraction data previously published by other researchers. The first reported observation of Pendellösung fringes in the III-V nitride material system is also presented.