Electrical characteristics of N-polar (0001) p-type GaN Schottky contacts

The electrical characteristics of Ni/N-polar p-GaN Schottky contacts were investigated in comparison with those of Ga-polar contacts. The Schottky barrier heights were obtained to be 0.91, 1.24, and 1.30 eV from the current-voltage (I-V), capacitance-voltage, and photoresponse results, respectively. These values of the N-polar samples were more than 1 eV lower than those of the Ga-polar samples. Hence, it was suggested that a Ni contact on N-polar p-GaN has a possible advantage in forming better ohmic electrodes. In addition, we also found that no memory effect, which was caused by the charge and discharge of surface defects [Ga vacancies (VGa)], was observed in the I-V characteristics, and no single peak of VGa was observed in the high-temperature isothermal capacitance transient spectroscopy spectrum. Therefore, it is suggested that the topmost N atomic layer can suppress the Ga out-diffusion.