Structural and optical properties of thick freestanding GaN templates

Structural and optical properties of thick (larger than 160 mum) freestandi ng hydride vapor phase epitaxy GaN templates have been investigated. AFM me asurements showed that flat and smooth surface could be fabricated. High-re solution X-ray diffraction studies carried out with different spectrometer slit for the symmetric and asymmetric diffractions show that the linewidth increases with increasing slits width. indicating that a considerable degre e of tilting and twisting of the individual grains are still present in the se thick samples. Raman scattering measurements performed in a few samples indicate good crystalline quality and reduced strain. Very sharp and intens e exciton related lines (FWHM less than I meV) have been observed in the lo w temperature photoluminescence spectra. Variable-temperature photoluminesc ence experiments were performed on both the growth surface and interface to identify the nature of the recombination processes observed in the lumines cence spectra. FTIR absorption measurements show the presence of at least t wo donors with binding energy of 30.5 and 33.6 meV. (C) 2001 Elsevier Scien ce B.V. All rights reserved.