Analysis of Non-ideal Ohmic Characteristics in Mg-incorporated P-type GaN Contacts

The formation of reliable p-type ohmic contacts remains a key challenge in GaN device technology. In this work, Mg incorporation pretreatment was employed to improve p-type GaN ohmic contacts, with the optimum annealing temperature identified as 550 ◦C for both Ni/Au and Pd/Ni/Au stacks. Secondary ion mass spectrometry (SIMS) confirmed enhanced Mg incorporation near the surface after annealing. Despite improved ohmic formation, the contacts exhibited non-ideal rectifying behavior, showing that contact resistance cannot be treated as a constant value or simply extracted from conventional TLM analysis. Instead, it must be considered as a current-dependent parameter. The influence of the non-ideal contact behavior on device performance was quantitatively analyzed using vertical PN diodes, showing that contact resistance accounted for a significant fraction of the total on-resistance at high current densities. These results highlight the need for current-dependent resistance models to enable accurate design and performance prediction of GaN-based devices.