Growth and characterization of bulk AlN substrates grown by PVT

We have grown bulk AlN boules by PVT at different growth temperatures. The grown material is single‐phase wurtzite AlN containing about 100 ppm wt of oxygen; transition metals are present only in the sub‐ppm range. Vibrational spectroscopy shows that structural quality of the single‐crystalline areas is high. In FT‐IR reflectivity, an additional maximum showing up in the 900–1000 cm–1 range is attributed to a probably distorted Al2O3 surface layer. In cathodoluminescence performed at 8 K, the samples show a broad luminescence band having its maximum varying between 3.45 eV and 3.85 eV as well as excitonic emission with transition energies of 6.03 eV, 5.93 eV and 5.82 eV. Remarkable variation in peak maximum and width of the broad band even within the same single‐crystalline area is probably caused by local inhomogeneities originating from fluctuations in impurity, e.g. oxygen, or defects concentration. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)