Hydride vapour-phase epitaxy growth and cathodoluminescence characterisation of thick GaN films

Hydride vapour-phase epitaxy of thick (12-120 mu m) GaN layers grown on unb uffered sapphire was examined. We found growth parameters such as the HCl f low rate and the distance from the mixing point to be critical determinants of the film quality. Good-quality films have been further examined by scan ning electron microscopy, cathodoluminescence spectroscopy and imaging. We have carried out spatially resolved studies of film cross-sections and top surfaces, as well as the interface side of free standing layers. The top su rface of the films show narrow bound exciton emission lines, while the cath odoluminescence spectra near the interface are broad and extend to energies above the band gap. We were able to quantify the electron concentration in those regions and found evidence of strong n-type doping (in the 10(19) cm (-3) range). Close to the interface we were able to directly observe a regi on about 10 mu m thick containing columnar structures which are highly n-ty pe doped. The highly doped columns occasionally protrude from the layer sur face. The relation between the defective region close to the substrate inte rface and the features observed at the top surface has been analysed. (C) 1 999 Elsevier Science B.V. All rights reserved.