Raman Mapping and Finite Element Analysis of Epitaxial Lateral Overgrown GaN on Sapphire Substrates

Using micro-Raman scattering and finite element (FE) analysis, stress fields in epitaxial lateral overgrown (ELO) GaN fabricated by metalorganic vapor phase epitaxy (MOVPE) on sapphire substrates using a two-step growth method were investigated. Nearly full stress relaxation at the top ELO GaN surface can be achieved by increasing the thickness of ELO GaN to about 50 μm. Reductions in stress variation between window and overgrown regions can be achieved by using a double ELO GaN growth at a much smaller ELO thickness. Increased compressive stress at the coalescence boundary of two adjacent wings of ELO GaN was related to the presence of voids in this area. In the double ELO growth, stress near the top surface was mainly attributed to the presence of voids on top of the upper dielectric mask.