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Dense ZnO(0001) films formed at 500°C via coalescence of islands grown via metalorganic vapor phase epitaxy (MOVPE) either on GaN/AlN/SiC(0001) substrates or on initial, coherent ZnO layers. Conical crystallites formed due to thermal expansion-induced stresses between the ZnO and the substrate. Interfaces between the ZnO films on GaN epilayers exposed either simultaneously to diethylzinc and oxygen or only to diethylzinc at the initiation of growth were sharp and epitaxial. Interfaces formed after the exposure of the GaN to O 2 were less coherent, though an interfacial oxide was not observed by cross-sectional transmission electron microscopy (TEM). Threading dislocations and stacking faults were observed in all films.

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Schottky contacts of Pt͑111͒ and Au͑111͒ were deposited on chemical-vapor-cleaned, n-type GaN͑0001͒ thin films. The growth mode of the deposition, as determined by x-ray photoelectron spectroscopy analysis, followed the two-dimensional Frank-van der Merwe growth model. The resulting as-deposited metal films were monocrystalline and epitaxial with a ͑111͒//͑0002͒ relationship with the GaN. Selected samples were annealed for three minutes at 400°C, 600°C or 800°C. The rectifying behavior of both contacts degraded at 400°C; they became ohmic after annealing at 600°C ͑Au͒ or 800°C ͑Pt͒. High-resolution transmission electron micrographs revealed reactions at the metal/GaN interfaces for the higher temperature samples. X-ray diffraction results revealed an unidentified phase in the Pt sample annealed at 800°C. A decrease in the room temperature in-plane ͑111͒ lattice constant for both metals, ranging from Ϫ0.1% to Ϫ0.5%, was observed as the annealing temperature was increased from 400 to 800°C. This plastic deformation was caused by tensile stresses along the ͓111͔ direction that exceeded the yield strength as a result of the large differences in the coefficients of thermal expansion between the metal contacts and the GaN film.