Electrical and structural properties of Au/Yb Schottky contact on p-type GaN as a function of the annealing temperature

The structural changes of Au/Yb contacts to p-type GaN were investigated using X-ray diffraction, X-ray photoemission spectroscopy, and atomic force microscopy as the annealing temperature was varied. The results were used to interpret the electrical properties of Au/Yb Schottky contacts to p-type GaN. A barrier height of 0.84 eV was obtained for the as-deposited Au/Yb/p-type GaN Schottky diode. An optimum barrier height of 1.03 eV was obtained for the 400 °C annealed Au/Yb/p-type GaN Schottky diode and the barrier height decreased after annealing at temperatures above 500 °C. Intermixing between the Au and Yb films occurred, implying an interfacial reaction between Au and Yb during deposition followed by a massive diffusion of Au towards GaN with increasing annealing temperature. The increase in the barrier height for the 400 °C annealed Au/Yb/p-type GaN contact could be associated with the formation of YbN phase, which creates nitrogen vacancies acting as donors in the vicinity of the metal/GaN interface region. The decrease in the barrier height after annealing at 500 and 600 °C could be due to the evolution of gallide phases, which generate Ga vacancies, leading to an increase in the net hole concentration near the metal/GaN interface.