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 37arcsec for the (101̄0) diffraction and 31 arcsec for the (202̄1) 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.