Properties of free-standing GaN bulk crystals grown by HVPE

GaN wafers 200 mu m thick and 30 mm diameter were fabricated. GaN was grown by hydride vapor phase epitaxy on SIC substrates and removed from the substrate by reactive ion etching. Lateral size of the GaN wafers was equal to the size of the initial SIC substrates. GaN wafers were cleaved in pieces and these pieces were characterised. It was found that after the fabrication, GaN crystals were slightly deformed and strained. An anneal at 830 degrees C in nitrogen ambient eliminated the residual strains. The FWHM of omega-scan (0002) x-ray rocking curve for annealed crystals was less than 140 arcsec for both sides of the best GaN crystals. The lattice constants measured from both sides of the crystals were c=5.1853+/-0.00038 Angstrom and a=3.1889+/-0.0001 Angstrom. The N-d-N-a concentration determined by a mercury probe was about 2x10(17)cm(-3) for as-grown GaN surface and about 2x10(19)cm(-3) for former interface surface. Photoluminescence spectrum taken at 17 K revealed an edge peak at 3.472 eV with the FWHM value of 2.3 meV. A ratio of the edge peak intensity to the intensity of yellow band was higher than 1000. Initial TEM experiments were performed.