Thin a-plane (1 1 2 0) GaN layers have been grown on r-plane (1 1 0 2) sapphire substrates by hydride vapor phase epitaxy (HVPE), using either a single-step high-temperature (HT) growth or a two-step growth method similar to that of metal organic vapor phase epitaxy (MOVPE). For the single-step growth procedure, layers were grown under various pressures, ranging from near atmospheric pressure down to 75 mbar. For growth pressures lower than 200 mbar, an improvement in surface morphology is observed. The full-widths at half-maximum (FWHM) of in-plane X-ray diffraction peak anisotropy features are reversed when the growth pressure is decreased from 400 to 100 mbar. These layers are then compared to those obtained by the two-step growth procedure. (c) 2006 Elsevier B.V. All rights reserved.