Raman study of the A1(LO) phonon in relaxed and pseudomorphic InGaN epilayers

Abstract

The behavior of the $A_1(\mathrm{LO})$ phonon mode of relaxed and pseudomorphic ${\mathrm{In}}_x{\mathrm{Ga}}_{\text{1−x}}\mathrm{N}$ epilayers, at the surface, is investigated by Raman spectroscopy. This study involves relaxed and pseudomorphic samples, with a compositional range of $\text{0.12⩽x<0.30}$ and $\text{0.04<x⩽0.20,}$ respectively. Raman measurements were performed under excitation at 3.71 eV. Due to the low depth penetration of the incident light (40 nm), the major contribution to Raman scattering comes from the surface, where strain and composition have been independently determined. For relaxed samples, a linear dependence of the $A_1(\mathrm{LO})$ phonon frequency is obtained, as theoretically expected for an one-mode behavior alloy: ${\Omega }_0\text{(x)=(736±1)-(149±2)x.}$ In the case of pseudomorphic samples, the phonon frequency is almost composition independent up to $\text{x=0.11,}$ probably due to the opposite effects of strain and alloying.