Temperature effect on the electronic structure of AlN

The temperature dependence of the optical reflectance spectra for aluminum nitride was measured on a high-quality single crystal with synchrotron radiation. The dominant structure due to the interband transition was observed at photon energy of 6.16 eV at room temperature. With decreasing temperature, the energy positions of the dominant structure in the reflectance spectra shift towards higher energies and this energy shift was found to be well described by the Bose-Einstein expression with the parameters obtained by absorption spectra measurements. The feature due to crystal-field and spin-orbit splitting of the valence was also observed around the interband transition, especially prominent at low temperatures.