Characterizing β-Ga2O3 by photoluminescence and Raman mapping

Monoclinic gallium oxide (β-Ga2O3) is an ultrawide bandgap semiconductor with potential applications in power electronics. Photoluminescence (PL) and Raman spectroscopy are important methods to characterize defects and inhomogeneities in this material. PL or Raman mapping with excitation wavelengths ranging from 266nm to 532nm reveals the spatial distribution of features with micron resolution or better. In Czochralski-grown β-Ga2O3, the Cr3+ emission intensity shows striations due to inhomogeneities during growth. In addition to defects in the bulk, PL microscopy has revealed several specific defects on the surface. Some of these localized centers are bright UV emitters. Homoepitaxial layers show defects that are observed via the shifts in the PL band, likely due to the strain field around a dislocation-like core. Damage due to high-intensity laser pulses results in significant changes in the intensity and energy of the UV band. β-Ga2O3 single crystals have a Raman mode at 250 cm-1 that arises from gallium clusters, defined as two or more Ga atoms that form Ga–Ga bonds.