High-pressure Raman scattering of biaxially strained GaN on GaAs

We present results of high-pressure Raman-scattering experiments on bulk GaN and GaN grown on GaAs. We determined the Gruneisen parameters of both the cubic TO and LO phonon modes and the hexagonal A(1), E-1 and E-2 modes. Our measurements reveal that the Gruneisen parameters for the GaAs substrate are about 30% smaller than those of bulk GaAs. This is a consequence of the lower compressibility of GaN compared to GaAs, which results in a pressure-induced biaxial strain on the substrate. From the pressure behavior of the GaAs modes and by comparing with our results for bulk GaN we obtained information about the biaxial strain in the GaN epitaxial layer.