Graded electrical breakdown method for obtaining excellent ohmic contact on nonpolar (112¯0) p-GaN

The graded electrical breakdown (EBD) method was introduced to obtain ohmic contact on nonpolar (112¯0) a-plane p-GaN surfaces. The graded EBD method, by which the electrical stress voltage could be increased up to 50V in the Ni/SiO₂/p-GaN structure, produced an ohmic contact with a specific resistance of 1.47 × 10^-3Ωcm² without any sudden degradation in the contact. Secondary ion mass spectroscopy measurements revealed that the ohmic contact was due to gallium vacancies generated near the SiO₂/p-GaN interface. Current-voltage-temperature measurements exhibited an insensitive temperature dependence of the contact resistance, indicating predominant tunneling transport at the contact.