Anisotropic optical constants, birefringence, and dichroism of wurtzite GaN between 0.6 eV and 6 eV

We report the room-temperature anisotropic dielectric functions (DFs), refractive indices, and absorption coefficients as well as birefringence and dichroism of wurtzite GaN in the spectral range between 0.6 eV and 6 eV. They have been determined by combined spectroscopic ellipsometry, optical retardation, and transmission measurements on a series of m- and c-plane bulk substrates prepared from crystals grown by hydride vapor phase epitaxy. The accuracy of the derived DFs is estimated by investigation of the role of mosaicity-related crystal imperfections, self-consistency test based on a Kramers-Kronig analysis, and examination of the influence of kind of overlayer. We also briefly discuss optical properties of a highly defective near-surface layer of GaN crystals introduced by their mechanical polishing.