Low-Resistance Nonalloyed Ti/Al Ohmic Contacts on N-Face n-Type GaN via an O-2 Plasma Treatment

Abstract

The authors report improved electrical properties of nonalloyed Ti/Al ohmic contact to N-face n-type GaN via oxygen (O-2) plasma treatment. The contact resistivity of Ti (50 nm)/Al (35 nm) electrodes is reduced significantly from 4.3 x 10(-1) Omega.cm(2) to 2.53 x 10(-5) Omega.cm(2) by applying O-2 plasma to the GaN surface before the Ti/Al deposition. In this process, Ti-N bonds are expected to form, while the Ga-N bonds are broken by the O-2 plasma, which eventually increases the nitrogen vacancies as well as the Ti-N phases at the GaN surface. This suggestion has been verified by X-ray photoelectron spectroscopy and transmission electron microscopy analyses.