Optical properties of bulk GaN crystals grown from solution at moderate pressure and temperature

Structural and optical properties of GaN crystals grown from solution at moderate temperature (800 °C) and pressure (∼0.25 Mpa) have been investigated using Raman scattering and photoluminescence spectroscopies. The lineshape and linewidth of the first-order optical phonons measured at room temperature indicates good crystalline quality of the freestanding GaN crystals and epitaxial GaN layers. Low-temperature photoluminescence spectra are characterized by sharp and intense emission peaks at 3.47 eV, attributed to the annihilation of excitons bound to shallow donors, which confirms good crystalline quality of the grown crystals and the epitaxial grown layers. The intensities of the near-bandedge emission lines in the photoluminescence spectra are consistent with reduced incorporation of pervasive background impurities in the crystals as well as in the epitaxial layers.