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The effect of impurities and defects on the optical properties of AlN was investigated. High-quality AlN single crystals of more than 20mm2 size were examined. Different crucible materials and growth procedures were applied to the growth of bulk AlN by physical vapor transport method to vary the defect and the impurity concentrations. The crystalline orientation was investigated by Raman spectroscopy. Glow discharge mass spectrometry was used to determine the trace concentration of the incorporated impurities such as oxygen and carbon. The photoluminescence emission and absorption properties of the crystals revealed bands around 3.5 and 4.3eV at room temperature. Absorption edges ranging between 4.1 and 5.95eV were observed. Since no straight correlation of the oxygen concentration was obtained, a major contribution of oxygen or oxygen-related impurities was ruled out to generate the observed emission and absorption bands in the Ultraviolet spectral range. The carbon-related impurities and intrinsic defects might contribute to the observed optical properties. The absorption coefficient for AlN single crystals has been derived for the spectral range below the band edge.

Group III-V wide band gap materials are widely used in developing solar blind, radiation-hard, high speed optoelectronic devices. A device detecting both ultraviolet ͑UV͒ and infrared ͑IR͒ simultaneously will be an important tool in fire fighting and for military and other applications. Here a heterojunction UV/IR dual-band detector, where the UV/IR detection is due to interband/intraband transitions in the Al 0.026 Ga 0.974 N barrier and GaN emitter, respectively, is reported. The UV threshold observed at 360 nm corresponds to the band gap of the Al 0.026 Ga 0.974 N barrier, and the IR response obtained in the range of 8-14 m is in good agreement with the free carrier absorption model.

Epitaxial layers of Ga 1−x Mn x N with concentrations of up to x = 0.015 have been grown on c-sapphire substrates by metalorganic chemical vapour deposition. No ferromagnetic second phases were detected via high-resolution x-ray diffraction. Crystalline quality and surface structure were measured by x-ray diffraction and atomic force microscopy, respectively. No significant deterioration in crystal quality and no increase in surface roughness with the incorporation of Mn were detected. Optical measurements show a broad emission band attributed to a Mn-related transition at 3.0 eV that is not seen in the underlying GaN virtual substrate layers. Room temperature ferromagnetic hysteresis has been observed in these samples, which may be due to either Mn-clustering on the atomic scale or the Ga 1−x Mn x N bulk alloy.

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