Thermal stability of the non-alloyed Pd/Sn and Pd/Ge ohmic contacts to n-GaAs

A novel non-alloyed Ohmic contact system comprising of Pd/Sn metallization has already been developed for n-type Gallium Arsenide (n-GaAS) [1]. Thermal stability of this metallization has not been reported yet. Thermal stability of novel Pd/Sn Ohmic contact has been investigated and compared to the non-alloyed Pd/Ge metallization. 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 (cTLM) method. The Pd(50 nm)/Sn(125 nm) contacts show a lowest rho(c) of 2.28 x 10(-5) Omega cm(2) on Si-doped 2 x 10(18) cm(-3) n-GaAs after annealing at 330 degrees C for 30 min, whereas the Pd(50 nm)/Ge(126 nm) contacts exhibit a lowest rho(c) of 2.84 x 10(-6) Omega cm(2) under the same annealing condition. The Pd/Sn Ohmic contacts display superior thermal stability at 410 degrees C when compared with the Pd/Ge contacts. After annealing at 410 degrees C for 4 h, rho(c) of the Pd(50 nm)/Sn(125 nm) metallization remains in the low 10(-5) Omega cm(2) range, whereas rho(c) values increase by approximately two orders of magnitude for the Pd(50 nm)/Ge(126 nm) contacts. (C) 1997 Elsevier Science S.A.