Abstract
The A exciton feature at 6.025 eV is observed directly in the low temperature (1.8 K) reflectance spectra of AlN for the first time, using a bulk AlN single crystal which has a relatively flat m‐face that allows both σ and π configurations. Features involving unresolved B and C excitons are also observed around 6.25 eV from this sample and in three c‐oriented MOCVD AlN films. Transmission measurements on the thickest film reveal a clear but weak A excitonic absorption feature at 6.080 eV. The results are explained by theoretical calculations of exciton energies and oscillator strengths. The calculations suggest that AlGaN light‐emitting devices will emit light mainly in the π polarization for wavelengths shorter than 320 nm.
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