Ex situ Ohmic contacts to n-InGaAs

The authors report ultralow specific contact resistivity (ρ _c) in ex situ Ohmic contacts to n -type In_0.53Ga _0.47 As (100) layers, with an electron concentration of 5× 1019 cm-3. They present the ρ _c obtained for molybdenum (Mo) contacts to n -type In_0.53Ga_0.47 As, with the semiconductor surface cleaned by atomic H before metal deposition. The authors compare these data with the ρ _c obtained for contacts made without atomic H cleaning. After exposure to air during normal device processing, the semiconductor surface was prepared by UV-ozone exposure plus a dilute HCl etch and subsequently exposed to thermally cracked H. Mo contact metal was deposited in an electron beam evaporator without breaking vacuum after H cleaning. Transmission line model measurements showed a contact resistivity of (1.1±0.9) × 10^-8 cm² ω for the Mo/In_0.53Ga_0.47 As interface. This ρ _c is equivalent to that obtained with in situ Mo contacts [ρ _c = (1.1±0.6) × 10^-8 cm²]. Ex situ contacts prepared by UV-ozone exposure plus dilute HCl (without any atomic H exposure) result in ρ _c = (1.5±1.0) × 10^-8 ω cm².