Effects of annealing cycles on the electrical and morphological characteristics of Pd/Sn ohmic contacts to n-GaAs

A novel Pd/Sn ohmic contact system is investigated for n-GaAs. The effects of annealing cycles on the electrical and morphological characteristics of the contacts are investigated using Scanning Electron Microscopy (SEM), surface profilometry measurements, Secondary Ion Mass Spectrometry (SIMS) and current-voltage (I-V) measurements. SEM and surface profilometry measurements are employed to investigate the surface morphology of the contacts. Contact depth profiles are analyzed by SIMS. Contact resistivities, p/sub c/, of the proposed metallization are measured utilizing a conventional Transmission Line Model (TLM) method. Annealing cycles show a significant effect on contact properties. Annealing at 360/spl deg/C for 30 min yielded the lowest p/sub c/ of /spl sim/3.26/spl times/10/sup -5/ /spl Omega/-cm/sup 2/ with Pd(30 nm)/Sn(150 nm) contacts. Two-step annealing improves both electrical and morphological characteristics of Pd/Sn contacts. A lowest p/sub c/ of /spl sim/1.49/spl times/10/sup -5/ /spl Omega/-cm/sup 2/ is obtained with same contacts under two-step annealing (225/spl deg/C, 50 s+350/spl deg/C, 15 min) condition. The SIMS depth profiles of the contacts are nearly identical for both types of annealing.