OXYGEN INCORPORATION IN ALUMINUM NITRIDE VIA EXTENDED DEFECTS .1. REFINEMENT OF THE STRUCTURAL MODEL FOR THE PLANAR INVERSION DOMAIN BOUNDARY

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[10 ($) over bar 11] + 1/3[0001] or 1/3[10 ($) over bar 11]. This thin sandwich is inserted onto the basal plane of the wurtzite structure of aluminum ni tride, This model does not take into consideration any interfacial rel axation phenomena, and is arguably electrically unstable. Therefore, t his paper presents a refinement of the model of Harris et al., by inco rporating the structural relaxations arising from modifications in loc al chemistry. The interfacial structure was investigated through the u se of conventional transmission electron microscopy, convergent electr on diffraction, high resolution transmission electron microscopy, anal ytical electron microscopy, and atomistic computer simulations, The re fined planar inversion domain boundary model is closely based on the o riginal model of Harris et al.; however, the local chemistry is change d, with every fourth oxygen being replaced by a nitrogen. Atomistic co mputer simulation of these defects, using a classical Born model of io nic solids, verified the stability of these defects as arising from th e adjustment in the local chemistry, The resulting structural relaxati ons take the form of a 0.3 mrad twist parallel to the interface, a con traction of the basal planes adjacent to the planar inversion domain b oundary, and an expansion of the c-axis component of the displacement vector; the new displacement vector across the interface is R = 1.3[10 ($) over bar 10] + epsilon[0001], where epsilon(meas) = 0.387 and eps ilon(calc) = 0.394.