Raman mapping of epitaxial lateral overgrown GaN: Stress at the coalescence boundary

Using micro-Raman scattering spectroscopy we have investigated stress fields in epitaxial lateral overgrown (ELO) GaN fabricated by metalorganic vapor phase epitaxy using a two-step growth method. The presence of an increased compressive stress at the coalescence boundary of two adjacent wings of ELO GaN was identified. From changes in the E2 (high) phonon frequency we estimate the magnitude of the stress concentration at the coalescence boundary to be on the order of ≈0.07 GPa with respect to the ELO GaN wing. Mechanisms for the stress concentration at the coalescence boundary were studied. Differences in stress and crystalline quality between wing and window regions of ELO GaN were also investigated.