Pressure dependence of the refractive index in wurtzite and rocksalt indium nitride

We have performed high-pressure Fourier transform infrared reflectance measurements on a freestanding InN thin film to determine the refractive index of wurtzite InN and its high-pressure rocksalt phase as a function of hydrostatic pressure. From a fit to the experimental refractive-index curves including the effect of the high-energy optical gaps, phonons, free carriers, and the direct (fundamental) band-gap in the case of wurtzite InN, we obtain pressure coefficients for the lowfrequency (electronic) dielectric constant e1 . Negative pressure coefficients of -8.8 × 10-2 GPa-1 and -14.8 × 10-2 GPa-1 are obtained for the wurtzite and rocksalt phases, respectively. The results are discussed in terms of the electronic band structure and the compressibility of both phases.The work was supported by the Spanish Ministry of Economy and Competitiveness (MINECO) under Project Nos. MAT2010-16116, MAT2012-38664-C02-2, and MALTA-CONSOLIDER INGENIO 2010 CSD2007-00045Peer Reviewe