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

Abstract

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±0.004eV (from I–V) and 0.622±0.018eV (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°C. The SBH of the Ni/Au Schottky contact for the other annealing temperature of 600°C was 0.617±0.005eV. The highest value of SBH for Ni/Au Schottky contact was obtained after annealing at 700°C and the value was 0.910±0.019eV. The variations in the chemical composition of the contacts with the annealing process were examined by XPS depth profile analysis.