Photoluminescence, raman and X-ray diffraction studies of porous GaN grown on sapphire

In this study, we have investigated the structural and optical properties of porous GaN films on sapphire (0001) prepared by UV assisted electrochemical etching. Scanning electron microscopy (SEM) and high resolution X-ray diffraction (HR-XRD) measurements reveal the nature of the pore morphology and microstructures. The optical properties of porous GaN samples have been studied by photoluminescence (PL) and Raman spectroscopy. SEM micrographs indicated that the average pore size for samples was around 0.16 to 0.43 μm. XRD revealed that the broadening in spectrum is due to the small size crystallites. As compared to the as-grown GaN films, porous layers exhibit a substantial photoluminescence (PL) intensity enhancement with red-shifted band- edge PL peaks associated with the relaxation of compressive stress. The shift of E2 (high) to the lower frequency in Raman spectra of the porous GaN films further confirms such a stress relaxation.