Ohmic Contact to High-Aluminum-Content AlGaN Epilayers

Abstract

We report on the effect of dry etching and the combination of metal stacks used to form ohmic contacts on silicon-doped high-Al-content (>60%) n-AlGaN layers for deep-ultraviolet light-emitting diodes. The contact characteristics are compared for as-grown and plasma-etched n-AlGaN samples. The Ti/Al/Ti/Au contacts to as-grown n-AlGaN were linear, with a specific contact resistivity of 5 × 10−5 Ω-cm2. The same metallic layer combinations yielded nonlinear contacts on the plasma-etched surface of the n-AlGaN layers. However, when Ni was used as the barrier layer instead of titanium, the contacts to plasma-etched AlGaN surfaces became linear, with a specific contact resistivity of 5 × 10−4 Ω-cm2.