Raman-scattering probe of anharmonic effects due to temperature and composition in InGaN

We have carried out a detailed investigation of temperature‐dependent micro‐Raman scattering on In1 − xGaxN films with different Ga compositions (0.06 ≤ χ ≤ 0.91). The observed phonon frequency downshift and linewidth broadening with increasing temperature of A1(LO) and E2(high) modes can be well explained by a model taking into account the contributions of the thermal expansion, the lattice‐mismatch‐induced strain, and the anharmonic phonon processes. We have elucidated the variation with Ga composition of the contribution of the three‐ and four‐phonon processes in the anharmonic effect. It is found that with increasing Ga composition the three‐phonon process increases over the four‐phonon process. The variation in the relative contribution from three‐ and four‐processes can be further attributed to the diversification of structural properties and phonon density of states in InGaN.