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

Abstract

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 $\ensuremath{\sim}143$ and $\ensuremath{\sim}569\text{ }{\text{cm}}^{\ensuremath{-}1}$, 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.