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_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°C for 30 min yielded the lowest p_c of ~3.26×10^-5 Ω-cm² with Pd(30 nm)/Sn(150 nm) contacts. Two-step annealing improves both electrical and morphological characteristics of Pd/Sn contacts. A lowest p_c of ~1.49×10^-5 Ω-cm² is obtained with same contacts under two-step annealing (225°C, 50 s+350°C, 15 min) condition. The SIMS depth profiles of the contacts are nearly identical for both types of annealing