Synchrotron-based photoluminescence excitation spectroscopy applied to investigate the valence band splittings in AlN and Al0.94Ga0.06N

We demonstrate that synchrotron-based photoluminescence excitation (PLE) spectroscopy is a versatile tool for determining valence band splittings of AlN and high aluminum content AlGaN. PLE results are independently confirmed by synchrotron-based spectroscopic ellipsometry. The splittings between the ordinary and the extraordinary absorption edges are found to be −240 meV and −170 meV for AlN and Al0.94Ga0.06N, respectively. These values differ from the crystal field energy due to residual strain.