Structural and optical properties of thick freestanding GaN templates

Abstract

Structural and optical properties of thick (larger than 160 μm) freestanding hydride vapor phase epitaxy GaN templates have been investigated. AFM measurements showed that flat and smooth surface could be fabricated. High-resolution 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 degree of tilting and twisting of the individual grains are still present in these thick samples. Raman scattering measurements performed in a few samples indicate good crystalline quality and reduced strain. Very sharp and intense exciton related lines (FWHM less than 1 meV) have been observed in the low temperature photoluminescence spectra. Variable-temperature photoluminescence experiments were performed on both the growth surface and interface to identify the nature of the recombination processes observed in the luminescence spectra. FTIR absorption measurements show the presence of at least two donors with binding energy of 30.5 and 33.6 meV.