Excitons and exciton-phonon coupling in the optical response of GaN



We carried out reflectance and spectroscopic ellipsometry measurements of high-purity c -plane epitaxial films of wurtzite GaN in a temperature range 5-840 K. Analysis of the data reveals three main contributions to the dielectric function related to optical transitions involving discrete exciton states, excitonic continuum and exciton-phonon complexes, respectively. The observed contributing mechanisms show different temperature dependence. This behavior is related to specific interactions between optical excitations and thermal LO phonons. (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)