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Structural, Optical, and Homoepitaxial Studies on the Bulk GaN Single Crystals Spontaneously Nucleated by the Na-Flux Method

Polarized and time-resolved photoluminescence (PL) studies were carried out on the bulk GaN single crystals spontaneously nucleated by the Na-flux method. Simultaneously, structural studies as well as homoepitaxial growth were carried out. For the bulk crystals, typical full width at half maximum values of X-ray rocking curves were 37 arcsec for the (1010) diffraction and 31 arcsec for the (2021) diffraction. Their PL spectra exhibited polarized excitonic fine structures at 9 K. A proper effective PL lifetime being 212 ps and the absence of distinct deep emission bands at room-temperature imply sufficiently low point defect concentrations. GaN homoepitaxial films grown on naturally formed six m-planes exhibited a smooth surface morphology with monolayer atomic steps, of which tilt and twist mosaics were just inherited from the substrate crystal. The results prove that Na-flux GaN crystals can be used as a seed for growing strain-free thick GaN crystals.