Oxygen incorporation in aluminum nitride via extended defects: Part II. Structure of curved inversion domain boundaries
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Robert A. Youngman Carborundum Microelectronics Company, 10409 S. 50th Place, Phoenix, Arizona 85044
Martha R. McCartney Center for Solid State Science, Arizona State University, Tempe, Arizona 85287
Alastair N. Cormack New York State College of Ceramics, Alfred University, Alfred, New York 14802
Michael R. Notis Department of Materials Science and Engineering, Lehigh University, Bethlehem, Pennsylvania 18015 (Received 2 June 1994; accepted 24 January 1995)
Three distinct morphologies of curved (curved, facetted, and corrugated) inversion domain boundaries (IDB's), observed in aluminum nitride, have been investigated using conventional transmission electron microscopy, convergent beam electron diffraction, high-resolution transmission electron microscopy, analytical electron microscopy, and atomistic computer simulations. The interfacial structure and chemistry of the curved and facetted defects have been studied, and based upon the experimental evidence, a single model has been proposed for the curved IDB which is consistent with all three observed morphologies. The interface model comprises a continuous nitrogen sublattice, with the aluminum sublattice being displaced across a {1011} plane, and having a displacement vector R = 0.23(0001). This displacement translates the aluminum sublattice from upwardly pointing to downwardly pointing tetrahedral sites, or vice versa, in the wurtzite structure. The measured 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 chemistry. This is supported by atomistic calculations which indicate that the interface is most stable when both aluminum vacancies and oxygen ions are present at the interface, and that the interface energy is independent 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 crystal. 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 both planar and curved IDB's. The Burgers vector for the dislocation present at the intersection of the planar and curved IDB's was determined to be b = l/3(10l0) + f(0001), where fmeas = 0.157 and fcalc = 0.164.
I. INTRODUCTION The presence of extended two-dimensional defects with two different morphologies in aluminum nitride (A1N), a planar variant and a curved variant, were first reported by Hagege et al.l and Westwood and Notis.2 These two morphologies can exist separately or they can be joined to form complex defects in which the two
a) Present
address: IBM Research Division, T. J. Watson Research Center, Yorktown Heights, New York 10598. J. Mater. Res., Vol. 10, No. 5, May 1995
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crystallographic variants alternate between planar and curved morphologies. In most cases, either when they exist sep
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