Spatial stress distribution and optical properties of GaN films grown on convex shape-patterned sapphire substrate by metalorganic chemical vapor deposition

μ-Raman and μ-photoluminescence methods have been employed to investigate microscopic spatial stress distribution and optical properties of GaN films grown on the convex shape-patterned sapphire substrate (CSPSS). By comparison of the μ-Raman and μ-PL spectra, we found that significantly large difference, Δσxx ∼0.46 GPa, in biaxial compressive stress between the flat trench and convex regions in the side facet of the GaN film, around ∼2 μm below the surface whereas on the GaN surface, little difference with large residual stress was observed in both regions compared to those from the side facet. Temperature dependent and time-resolved photoluminescence spectra have shown that the GaN film grown on the CSPSS has improved crystal purity through the reduction of intrinsic point defects.

Research highlights▶ The local stress distribution of the GaN films grown on the convex-shaped patterned sapphire substrate is examined using μ-Raman scattering. ▶ We find that there is significant stress reduction in the flat trench due to stress relaxation by lateral growth but large thermal stress is built in the GaN surface. ▶ Photoluminescence results show improved crystal purity of the GaN film via the reduced native point defects.