Formation of Vanadium-based Ohmic Contacts to n-GaN

Abstract

We investigate vanadium (V)-based Ohmic contacts on n-GaN (<TEX>$N_{d}$</TEX>=<TEX>$2.0<TEX>${\times}$</TEX>10^{18}$</TEX> <TEX>$cm^{-3}$</TEX> ) as a function of annealing temperature. It is shown that the V (60 nm) contacts become Ohmic with specific contact resistances of <TEX>$10^{-3}$</TEX> <TEX>$- 10^{-4}$</TEX> Ω<TEX>$\textrm{cm}^2$</TEX> upon annealing at 650 and <TEX>$850^{\circ}C$</TEX>. The V(20 nm)/Ti(60 nm)/Au(20 nm)contacts produce very low specific contact resistances of <TEX>$2.2 <TEX>${\times}$</TEX> 10^{-5}$</TEX> and<TEX>$ 4.0<TEX>${\times}$</TEX>10^{-6}$</TEX> Ω<TEX>$\textrm{cm}^2$</TEX> when annealed at 650 and <TEX>$850{\circ}C$</TEX>, respectively. A comparison shows that the use of the overlayers (Ti/Au) is very effective in improving Ohmic property. Based on the current-voltage measurement, Auger electron spectroscopy, glancing angle X-ray diffraction, and X-ray photoemission spectroscopy results, the possible mechanisms for the annealing temperature dependence of the Ohmic behavior of the V-based contacts are described and discussed.d.