Low resistance copper-based ohmic contact for AlGaN/GaN high electron mobility transistors

Abstract

Ti/Al/Ni/Cu ohmic contact for AlGaN/GaN structure has been fabricated. The Ni layer played an important role in achieving low specific contact resistance (r(c)), smooth morphology, and excellent edge acuity. With a 50-angstrom Ni layer, a r(c) of 1.35 x 10(-6) Omega-cm(2) and a root-mean-square roughness of 7.65 nm have been realized. The characterization results indicated that no evidence of Cu diffusion into the semiconductor layers. The formation of Al-Cu and Ti-Cu alloys might have confined the Cu within the ohmic metal. In the absence of gold, the surface roughening caused by Au-Al alloy in conventional Ti/Al/Ni/Au structure was also prevented. (C) 2013 AIP Publishing LLC.