Al-based contacts on Ga-face and N-face n-GaN wafer grown by using hydride vapor phase epitaxy

The effect of crystal polarity on the electrical properties of Al-based contacts to the Ga-face and the N-face n-GaN wafer has been investigated. The Al-based contacts prepared on the Ga-face n-GaN wafer exhibited linear I-V characteristics after annealing at 500°C for 90 min. On the contrary, the contacts on the N-face n-GaN wafer showed a nonlinear I-V curve. X-ray photoemission spectroscopy indicated that AlN could be produced at the interface between GaN and the contact metals after the annealing. High-resolution photoemission spectroscopy suggested that the differences in I-V characteristics of the Al-based contacts on the Ga-face and the N-face n-GaN could be explained by opposite piezoelectric fields at the GaN/AlN heterostructure resulting from different polarities of the GaN wafer.