Investigation of low-resistance metal contacts on p-type GaN using the linear and circular transmission line method

In this work we investigated the specific contact resistances of the differ ent metallizations Pt, Pd, and Ni on p-type GaN. Those materials were depos ited both by thermal and electron beam evaporation on LED wafer material gr own on SiC by MOCVD after using a standard surface treatment. Realizing var ious annealing steps we were able to achieve results in the low 10(-3) Omeg a cm(2) range. To determine those values, TLM (transmission line method) pa tterns were made by photolithography technique. To proof the usability of t he TLM measurements on LED wafer material a comparison of the results obtai ned by linear and circular test structures with different geometries is giv en. Furthermore, the Pt, Pd and Ni contacts were examined by temperature de pendent TLM measurements to get information concerning the current transpor t mechanism at the p-GaN-metal interface. The experiments showed only a wea k temperature dependence of the contact resistances which indicates that ma inly the field emission determines the contact resistance.