Photoluminescence spectra of high-quality bulk AlN crystals are reported. In addition to the expected linear luminescence features like free excitons and donor-bound excitons, nonlinear processes like biexcitons and the exciton-exciton scattering band are seen for higher excitation densities. For temperatures above $\approx 150\text{K}$ the electron-hole plasma becomes clearly visible in the spectra. A detailed analysis of the data yields an exciton binding energy of 55 meV, a biexciton binding energy of 28.5 meV, a band gap of 6.089 eV at low temperature, and a band gap of 6.015 eV at room temperature.

• Received 29 December 2009

DOI:https://doi.org/10.1103/PhysRevB.82.075208