Spatially resolved photoluminescence and Raman mapping of epitaxial GaN laterally overgrown on sapphire

We report spatially resolved photoluminescence (PL) and micro-Raman scattering studies of epitaxial lateral overgrowth (ELO) of GaN on a SiO2 -masked sapphire substrate. Near-field scanning optical microscope measurements show that the ELO layers exhibit strong band-edge emission and yellow-band emission. Raman spectra reveal E₂ (low) and E₂ (high) phonon modes at ∼143 and ∼569 cm^-1, respectively. Interestingly, the E₂ (high) phonon intensity is significantly increased in the ELO layers. Furthermore, minima of the spectral widths of this mode occur in the ELO layers. The E₂ (low) phonon mode exhibits similar behavior, that is, its intensity is stronger in ELO GaN on SiO ₂ stripes than in coherently grown GaN on the mask openings. PL and Raman results suggest that crystalline quality is enhanced and threading dislocation density is reduced in the ELO layers.