Effect of thermal annealing on electrical and structural properties of Ni/Au/n-GaN Schottky contacts

The effects of thermal annealing on the electrical and structural properties of Ni/Au Schottky contacts to n-type GaN were investigated by current-voltage (I-V) and capacitance-voltage (C-V) characteristics, atomic force microscopy (AFM), and X-ray photoelectron spectroscopy (XPS) depth profile analysis. The metallization patterns on GaN grown by metal organic chemical vapor deposition (MOCVD) on a (0001) sapphire substrate were formed using the photolithography and lift-off techniques. The Schottky barrier height (SBH) for these contacts was obtained from I-V and C-V measurements. The value of SBH of the as-deposited contacts was found to be 0.560 +/- 0.004 eV (from I-V) and 0.622 +/- 0.018 eV (from C-V) with an ideality factor of 1.856 +/- 0.085. The values of SBH obtained from the C-V measurements were found to be higher than that of obtained from the I-V measurements. This case was attributed to the presence of the lateral inhomogeneities of the barrier height. However, the values of SBH slightly increase after the annealing temperatures at 100, 200, 300, 400 and 500 degrees C. The SBH of the Ni/Au Schottky contact for the other annealing temperature of 600 degrees C was 0.617 +/- 0.005 eV. The highest value of SBH for Ni/Au Schottky contact was obtained after annealing at 700 degrees C and the value was 0.910 +/- 0.019 eV. The variations in the chemical composition of the contacts with the annealing process were examined by XPS depth profile analysis. (C) 2014 Elsevier B.V. All rights reserved.