Influence of rapid thermal annealing on electrical and structural properties of Pd/Au Schottky contact to Ga-polarity GaN grown on Si (111) substrate

Abstract

Abstract We studied the effect of high temperature rapid thermal annealing on the electrical and structural properties of Pd/Au Schottky contact to Ga-polarity GaN grown by MBE on p-Si substrate. Current-voltage (I-V), capacitance-voltage (C-V), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD) and atomic force microscopy (AFM) measurements are performed for the electrical and structural characterization of the Schottky diode. It has been observed that there is a significant improvement in barrier height and ideality factor with reduction in leakage current upon annealing. The estimated Schottky barrier height (φ B0 ) for the as-deposited contact is 0.61eV (I-V) and 0.94 eV (C-V). While, the extracted barrier height for 700 °C annealed contact is improved to 0.74 eV (I-V) and 1.09 eV (C-V). In addition, the surface state density is calculated using C-V and it is found that there is ten time reduction in surface state density for 700 °C annealed Pd/Au Schottky contact compared to the as-deposited Schottky contact to semiconductor. X-ray photoelectron spectroscopy (XPS) depth profile results showed that there is out diffusion of Ga into metal film which may have formed metal-gallide phases for the annealed Schottky contacts that was confirmed by X-ray diffraction (XRD) results. It implies a reduction in nitrogen related vacancies and dangling bonds associated with GaN, which could be the reason for increase in the Schottky barrier height. Moreover, the surface morphology of the contacts is analysed by atomic force microscopy (AFM) and it is found that the surface roughness of Schottky contact does not degraded upon annealing. This indicates that the contacts were thermally stable during annealing.