Characterization of bulk GaN crystals grown from solution at near atmospheric pressure

The properties of GaN crystals grown from solution at temperatures ranging from 780 to 810 degrees C and near atmospheric pressure similar to 0.14 MPa, have been investigated using low temperature X-band (similar to 9.5 GHz) electron paramagnetic resonance spectroscopy, micro-Raman spectroscopy, photoluminescense spectroscopy, and photoluminescence imaging. Our samples are spontaneously nucleated thin platelets of approximate dimensions of 2 x 2 x 0.025 mm(3), or samples grown on both polycrystalline and single crystal HVPE large-area (similar to 3 x 8 x 0.5 mm(3)) seeds. Electron paramagnetic resonance spectra consists of a single Lorentzian line with axial symmetry about the c-axis, with approximate g-values, g(parallel to) = 1.951 and g(perpendicular to) = 1.948 and a peak-to-peak linewidth of similar to 4.0 G. This resonance has been previously assigned to shallow impurity donors/conduction electrons in GaN and attributed to Si- and/or O impurities. Room temperature photoluminescence and photoluminescence imaging data from both Ga- and N-faces show different dominant emission bands, suggesting different incorporation of impurities and/or native defects. Raman scattering and X-ray diffraction show moderate to good crystalline quality. (C) 2010 Elsevier B.V. All rights reserved.