High-pressure Raman scattering in InGaN heteroepitaxial layers: Effect of the substrate on the phonon pressure coefficients

We perform high-pressure Raman-scattering measurements on different In xGa1-xN/Si(111) epilayers (0.19 < x < 0.45). We find that the experimental pressure coefficient of the A 1(LO) mode measured in these samples is larger than that expected from the linear interpolation between the corresponding values of GaN and InN. Similar measurements in InGaN epilayers grown on GaN/sapphire templates yield much lower values, below the linearly interpolated pressure coefficients. We conclude that the phonon pressure coefficients measured in InGaN are mainly determined by the different compressibility of the substrate and epilayer material. Neglecting substrate effects may yield highly inaccurate phonon pressure coefficients and mode Grüneisen parameters.
The work was supported by the Spanish Ministry of Economy and Competitiveness (MINECO) under project MAT2010-16116.