A comparative study of Pd/Sn/Au, Au/Ge/Au/Ni/Au, Au-Ge/Ni and Ni/Au-Ge/Ni ohmic contacts to n-GaAs

Abstract

A comparative study is presented of newly developed Pd/Sn/Au and conventional alloyed Au/Ge/Au/Ni/Au, Au-Ge/Ni and Ni/Au-Ge/Ni ohmic contacts to n-GaAs. Metallization samples are furnace annealed at various temperatures and systematically characterized utilizing Scanning Electron Microscopy (SEM) and current–voltage ( I– V) measurements. Contact resistivities, ρ c, of the proposed metallizations are measured using a conventional Transmission Line Model (TLM) method. A lowest ρ c of 8.13×10 −6 Ω cm 2 is obtained with the Pd(50 nm)/Sn(125 nm)/Au(100 nm) contacts on Si-doped 2×10 18 cm −3 n-GaAs after annealing at 300°C for 30 min. The five-layer Au(14 nm)/Ge(14 nm)/Au(14 nm)/Ni(11 nm)/Au(200 nm) contacts show improved characteristics when compared to the conventional alloyed Au-Ge(150 nm)/Ni(16 nm) and Ni(5 nm)/Au-Ge(150 nm)/Ni(16 nm) metallizations with a ρ c of 6.49×10 −6 Ω cm 2 after alloying at 430°C for 6 min. The Pd/Sn/Au ohmic contacts display comparable thermal stability at 410°C to the alloyed Au/Ge/Au/Ni/Au contacts. After annealing at 410°C for 10 h, ρ c of the Pd(50 nm)/Sn(125 nm)/Au(100 nm) metallizations remain in the low 10 −5 Ω cm 2 range.