Aluminum nitride possesses a unique ability to accommodate oxygen via lattice dissolution to levels exceeding 4 at.%. The mechanism for this large accommodation of oxygen is of technological and scientific interest due to the established deleterious effects of oxygen on the thermal conductivity in this material. When doped with oxygen, AIN exhibits an intense, very broad (FWHM > 1 eV), luminescence peak in the near-UV (-375 nm). Though there is little doubt that this transition is associated with oxygen incorporation in the lattice, both the anomalous width of this feature and the specific complex from which it is derived have been a matter of debate. This paper reviews past studies of the luminescence of oxygen-related defects in AIN and presents recent detailed photoluminescence experiments which delineate changes in the luminescence as a function of oxygen content. These data are utilized in conjunction with other measurements to elucidate the nature of the oxygen-related defect and its evolution as a function of oxygen concentration. A defect-cluster model is presented which accounts for a transition in the luminescent properties of AIN and is found to be in accord with measurements on thermal conduction and unit-cell volume changes in AIN. This understanding of the oxygen-related defect in AIN from the photoluminescence studies is then utilized in cathodoluminescence studies via cathodoluminescence imaging in a scanning electron microscope and a transmission electron microscope. Such techniques are extremely useful in elucidating the distribution and interaction of oxygen in the microstructure of sintered AIN ceramics, which has been heretofore an extremely difficult problem in microstructural and microchemical analysis of such sintered ceramics. [

The oxygen-related defect in an aluminum nitride (A1N) single crystal and in polycrystalline ceramics is investigated utilizing photoluminescence spectroscopy, thermal conductivity measurements, x-ray diffraction lattice parameter measurements, and transmission electron microscopy. The results of these measurements indicate that at oxygen concentrations near 0.75 at. %, a transition in the oxygen accommodating defect occurs. On both sides of this transition, simple structural models for the oxygen defect are proposed and shown to be in good agreement with the thermal conductivity and lattice parameter measurements, and to be consistent with the formation of various extended defects (e.g., inversion domain boundaries) at higher oxygen concentrations.

The model proposed by Harris et al. [J. Mater. Res. 5, 1763–1773 (1990)], describing planar inversion domain boundaries in aluminum nitride, consists of a basal plane of aluminum atoms octahedrally coordinated with respect to oxygen, and with a translation of R = 1/3〈1011〉. This thin sandwich is inserted onto the basal plane of the wurtzite structure of aluminum nitride. This model does not take into consideration any interfacial relaxation phenomena, and is arguably electrically unstable. Therefore, this paper presents a refinement of the model of Harris et al., by incorporating the structural relaxations arising from modifications in local chemistry. The interfacial structure was investigated through the use of conventional transmission electron microscopy, convergent electron diffraction, high resolution transmission electron microscopy, analytical electron microscopy, and atomistic computer simulations. The refined planar inversion domain boundary model is closely based on the original model of Harris et al.; however, the local chemistry is changed, with every fourth oxygen being replaced by a nitrogen. Atomistic computer simulation of these defects, using a classical Born model of ionic solids, verified the stability of these defects as arising from the adjustment in the local chemistry. The resulting structural relaxations take the form of a 0.3 mrad twist parallel to the interface, a contraction of the basal planes adjacent to the planar inversion domain boundary, and an expansion of the c-axis component of the displacement vector; the new displacement vector across the interface is R = 1.3〈1010〉 + ∊〈0001〉, where ∊meas = 0.387 and ∊calc = 0.394.

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