Thermally stable and low-resistance W/Ti/Au contacts to n-type GaN

We report on the formation of thermally stable and low-resistance Ti/Au-based ohmic contacts to n-type GaN (4.0 x 10(18) cm(-3)) by using a W barrier layer. It is shown that the electrical characteristic of the sample is considerably improved upon annealing at 900 A degrees C for 1 min in a N-2 ambient. The contacts produce the specific contact resistance as low as 6.7 x 10(-6) Omega cm(2) after annealing. The Norde and current-voltage methods are used to determine the effective Schottky barrier heights (SBHs). It is shown that annealing results in a reduction in the SBHs as compared to that of the as-deposited sample. Auger electron spectroscopy (AES), scanning transmission electron microscopy (STEM) and X-ray diffraction (XRD) examinations show that nitride and gallide phases are formed at the contact/GaN interface. Based on the AES, STEM and XRD results, a possible ohmic formation mechanism is described and discussed