Thick GaN layers grown on A-plane sapphire substrates by hydride vapour phase epitaxy

We report on the crystal quality of GaN thick layers grown on a-plane sapphire by hydride vapour phase epitaxy (HVPE) using X-ray diffraction (XRD), atomic force microscopy (AFM) and low temperature photoluminescence (PL). The films have been grown in a horizontal reactor without a buffer layer on a-plane sapphire. For comparison some layers have been grown on c-plane sapphire substrates. The growth rate has been studied as a function of HCl gas how and the highest value has been estimated to be 106 mu m/h. The effect of different growth conditions on film properties is discussed. The X-ray diffraction measurements show that the layers obtained by HVPE on a-oriented sapphire without buffer layers have a high crystalline perfection with a rocking curve full width at half maximum (FWHM) of the (0002) reflection of about 4 arcmin. This value is comparable to those reported for high quality MOVPE material. The photoluminescence spectra measured at 2 K show the free exciton lines and narrow bound exciton lines of about 2 meV halfwidth, also indicating that the GaN thick layers grown on a-plane sapphire are of high crystalline quality.