Low‐Temperature Processing to Obtain Contact Resistance of <0.03 Ohm mm to Boron‐Doped Diamond

Abstract

Low‐resistance Ohmic contacts are necessary for high‐performance electronic devices. Ultrawide‐bandgap semiconductor materials typically have high‐resistance Ohmic contacts between the metal contact and the semiconductor. For single‐crystal boron‐doped diamond, with a bandgap of 5.5 eV, the reported specific contact resistance values vary from &gt;10−3 Ω cm2 to the lowest reported value of 2 × 10−7 Ω cm2. To obtain this low‐resistance Ohmic contact, a high temperature, &gt;500 °C, annealing is usually required, which can limit fabrication procedures and compromise device designs. On p‐type single‐crystal diamond, the lowest reported contact resistance is 0.39 Ω mm. This article reports specific contact resistances of 8.2 × 10−8 to 3.6 × 10−7 Ω cm2 and contact resistances 0.027 to 0.041 Ω mm, which are significantly better than reports in the literature and are achieved without the annealing step. The results are achieved by reactive ion etching 10 to 20 nm into the boron‐doped diamond surface. After the etch, evaporated Ti/Au forms Ohmic contacts with resistances between 0.08 and 0.2 Ω mm without an anneal. An additional step of exposing the etched surface to an intense H2 plasma at 700 °C before Ti/Au deposition, results in Ohmic contacts between 0.027 and 0.041 Ω mm.