Band-edge exciton states in AlN single crystals and epitaxial layers

The band-edge excitonic properties of AlN are investigated using low-temperature (1.7K) optical reflectance and transmission measurements of samples with various crystal orientations. The A, B, and C excitons are found to have energies of 6.025, 6.243, and 6.257eV in unstrained material, which shift with strain. The results are compared to a calculation of exciton energies and oscillator strengths to yield a crystal-field splitting of −230meV in unstrained AlN, in good agreement with previous ab initio calculations.