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

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, rho(c), of the proposed metallizations are measured using a conventional Transmission Line Model (TLM) method. A lowest rho(c) of 8.13 x 10(-6) Ohm cm(2) is obtained with the Pd(50 nm)/Sn(125 nm)/Au(100 nm) contacts on Si-doped 2 x 10(18) cm(-3) n-GaAs after annealing at 300 degrees C for 30 min. The five-layer Au(14 nm)/Ge(l4 nm)/Au(14 nn)/Ni(11 nm)/Au(200 nm) contacts show improved characteristics when compared to the conventional alloyed Au-Ge(150 nn)/Ni(16 nm) and Ni(5 nm)/Au-Ge(150 nm)/Ni(16 nn) metallizations with a rho(c) of 6.49 x 10(-6) Ohm cm(2) after alloying at 430 degrees C for 6 min. The Pd/Sn/Au ohmic contacts display comparable thermal stability at 410 degrees C to the alloyed Au/Ge/Au/Ni/Au contacts. After annealing at 410 degrees C for 10 h, rho(c) of the Pd(50 nm)/Sn(125 nm)/Au(100 nm) metallizations remain in the low 10(-5) Ohm d cm(2) range.