Low-Resistance Nonalloyed Ti/Al Ohmic Contacts on N-Face n-Type GaN via an $\hbox{O}_{2}$ Plasma Treatment

Abstract

The authors report improved electrical properties of nonalloyed Ti/Al ohmic contact to N-face n-type GaN via oxygen (O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ) plasma treatment. The contact resistivity of Ti (50 nm)/ Al (35 nm) electrodes is reduced significantly from 4.3 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> Ω · cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> to 2.53 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-5</sup> Ω · cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> by applying O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> 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 <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> 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.