Electrical, structural and microstructural characteristics of as-deposited and annealed Pt and Au contacts on chemical-vapor-cleaned GaN thin films
Schottky contacts of Pt(111) and Au(111) were deposited on chemical-vapor-cleaned, n-type GaN(0001) 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 (111)//(0002) relationship with the GaN. Selected samples were annealed for three minutes at 400 degreesC, 600 degreesC or 800 degreesC. The rectifying behavior of both contacts degraded at 400 degreesC; they became ohmic after annealing at 600 degreesC (Au) or 800 degreesC (Pt). 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 degreesC. A decrease in the room temperature in-plane (111) lattice constant for both metals, ranging from -0.1% to -0.5%, was observed as the annealing temperature was increased from 400 to 800 degreesC. This plastic deformation was caused by tensile stresses along the  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. (C) 2002 American Institute of Physics.