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.
Electrical, structural and microstructural characteristics of as-deposited and annealed Pt and Au contacts on chemical-vapor-cleaned GaN thin films
Preble, EA., Tracy, KM., Kiesel, S., McLean, H., Miraglia, PQ., Nemanich, RJ., Davis, RF., Albrecht, M., & Smith, DJ. (2002). Electrical, structural and microstructural characteristics of as-deposited and annealed Pt and Au contacts on chemical-vapor-cleaned GaN thin films. Journal of Applied Physics, 91(4), 2133-2137.