We report spatially resolved photoluminescence (PL) and micro-Raman scattering studies of epitaxial lateral overgrowth (ELO) of GaN on a ${\text{SiO}}_2$-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 $E_2$ (low) and $E_2$ (high) phonon modes at $\sim 143$ and $\sim 569{\text{cm}}^{-1}$, respectively. Interestingly, the $E_2$ (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 $E_2$ (low) phonon mode exhibits similar behavior, that is, its intensity is stronger in ELO GaN on ${\text{SiO}}_2$ 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.

• Received 26 April 2010

DOI:https://doi.org/10.1103/PhysRevB.81.233304