Near Bandedge Cathodoluminescence Studies of AlN Films: Dependence on MBE Growth Conditions

Aluminum nitride films were grown by molecular beam epitaxy on sapphire (0001) substrates. In some samples, alternating GaN/AlN thin layers were incorporated prior to the deposition of the main AlN layer in an effort to possibly reduce defects. The cathodoluminescence spectra show a sharp bandedge peak, which we tentatively assign to the optical recombination of a donor bound exciton (D0,X), sometimes accompanied by weak one- and two-longitudinal optical phonon replicas. There is also a broad band with maxima in the range 3200–3700 Å. A large value for the ratio (D0,X)/(broad band) tends to be associated with a narrow (D0,X) linewidth.