Ohmic contacts to n-type GaAs made with Pd/Sn and Pd/Sn/Au metallizations

Abstract

A non-alloyed ohmic contact system comprising of Pd/Sn metallization has been developed for n-GaAs and compared with Pd/Sn/Au metallization. Contacts are annealed at 300-400/spl deg/C for 30 min in a graphite strip annealer. Surface morphology of the contacts is investigated using surface profilometry measurements and Scanning Electron Microscopy (SEM). Contact resistivities, /spl rho//sub c/, of the proposed metallizations are measured utilizing conventional Transmission Line Model (TLM) method. A lowest /spl rho//sub c/ of 2.38/spl times/10/sup -5/ /spl Omega/-cm/sup 2/ is obtained with Pd(40 nm)/Sn(120 nm) contacts on 2/spl times/10/sup 18/ cm/sup -3/ n-GaAs after annealing at 400/spl deg/C for 30 min. A Au overlayer improves both electrical and morphological characteristics of the contacts. The Au overlayer also changes the optimal annealing cycles at the lowest /spl rho//sub c/ points. The Pd(30 nm)/Sn(150 nm)/Au(100 nm) contact shows a lowest /spl rho//sub c/ of /spl sim/3.89/spl times/10/sup -6/ /spl Omega/-cm/sup 2/ after annealing at 330/spl deg/C for 30 min. The Pd(30 nm)/Sn(90 nm) contact is thermally stable at 300/spl deg/C for at least 400 h. After 400 h annealing, /spl rho//sub c/ values decrease from 1.13/spl times/10/sup -3/ to 1.37/spl times/10/sup -5/ /spl Omega/-cm/sup 2/.