OXYGEN INCORPORATION IN ALUMINUM NITRIDE VIA EXTENDED DEFECTS .2. STRUCTURE OF CURVED INVERSION DOMAIN BOUNDARIES AND DEFECT FORMATION

Three distinct morphologies of curved (curved, facetted, and corrugate d) inversion domain boundaries (IDB's), observed in aluminum nitride, have been investigated using conventional transmission electron micros copy, convergent beam electron diffraction, high-resolution transmissi on electron microscopy, analytical electron microscopy, and atomistic computer simulations, The interfacial structure and chemistry of the c urved and facetted defects have been studied, and based upon the exper imental evidence, a single model has been proposed for the curved IDB which is consistent with all three observed morphologies, The interfac e model comprises a continuous nitrogen sublattice, with the aluminum sublattice being displaced across a {10 ($) over bar 11} plane, and ha ving a displacement vector R = 0.23[0001], This displacement translate s the aluminum sublattice from upwardly pointing to downwardly pointin g tetrahedral sites, or vice versa, in the wurtzite structure, The mea sured value of the displacement vector is between 0.05[0001] and 0.43[ 0001]; the variation is believed to be due to local changes in chemist ry. This is supported by atomistic calculations which indicate that th e interface is most stable when both aluminum vacancies and oxygen ion s are present at the interface, and that the interface energy is indep endent of displacement vector in the range of 0.05(0001) to 0.35[0001] , The curved IDB's form as a result of nonstoichiometry within the cry stal. The choice of curved IDB morphology is believed to be controlled by local changes in chemistry, nonstoichiometry at the interface, and proximity to other planar IDB's (the last reason is explained in Part III), A number of possible formation mechanisms are discussed for bot h planar and curved IDB's. The Burgers vector for the dislocation pres ent at the intersection of the planar and curved IDB's was determined to be b = 1/3[10 ($) over bar 10] + t[0001], where t(meas) = 0.157 and t(calc) = 0.164.