Photoreflectance spectra of excitonic polaritons in GaN substrate preparedby lateral epitaxial overgrowth

Photoreflectance (PR) spectra of high-purity, nearly free-standing GaN subs trate were compared with emission and reflectance spectra, which were analy zed based on a model exciton-polariton picture in which A, B, and C free ex citons couple simultaneously to an electromagnetic wave. The GaN substrate with reduced dislocation density was prepared by lateral epitaxial overgrow th technique and it exhibited predominant excitonic emissions with the deca y time nearly 1 ns even at room temperature. The transition energies obtain ed from the PR spectrum agree with the energies of bottlenecks of the excit onic polariton branches. The result means that perturbation-induced change in the dielectric function is mainly due to polaritons. Temperature depende nce of the A-exciton energy was well described using a model which assumes Einstein phonons. (C) 2000 American Institute of Physics. [S0003-6951(00)00 412-5].