Investigation of Low-Resistance Metal Contacts on p-Type GaN Using the Linear and Circular Transmission Line Method

Abstract

In this work we investigated the specific contact resistances of the different metallizations Pt, Pd, and Ni on p-type GaN. Those materials were deposited both by thermal and electron beam evaporation on LED wafer material grown on SiC by MOCVD after using a standard surface treatment. Realizing various annealing steps we were able to achieve results in the low 10–3 Ω cm2 range. To determine those values, TLM (transmission line method) patterns were made by photolithography technique. To proof the usability of the TLM measurements on LED wafer material a comparison of the results obtained by linear and circular test structures with different geometries is given. Furthermore, the Pt, Pd and Ni contacts were examined by temperature dependent TLM measurements to get information concerning the current transport mechanism at the p-GaN–metal interface. The experiments showed only a weak temperature dependence of the contact resistances which indicates that mainly the field emission determines the contact resistance.