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

Abstract

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, ρ 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 ρ c of 2.28×10 −5 Ωcm 2 on Si-doped 2×10 18 cm −3 n-GaAs after annealing at 330°C for 30 min, whereas the Pd(50 nm)/Ge(126 nm) contacts exhibit a lowest ρ c of 2.84×10 −6 Ωcm 2 under the same annealing condition. The Pd/Sn Ohmic contacts display superior thermal stability at 410°C when compared with the Pd/Ge contacts. After annealing at 410°C for 4 h, ρ c of the Pd(50 nm)/Sn(125 nm) metallization remains in the low 10 −5 Ωcm 2 range, whereas ρ c values increase by approximately two orders of magnitude for the Pd(50 nm)/Ge(126 nm) contacts.