Characterization of Pd/Sn ohmic contacts on n-GaAs using electrical measurements, EDAX and SIMS

A non-alloyed Pd/Sn ohmic contact on n-GaAs has been developed. Metallization samples are: annealed at various temperatures and systematically characterized using Energy Dispersive Analysis of X-rays (EDAX), Secondary Ion Mass Spectrometry (SIMS) and current-voltage (I-V) measurements. Contact resistivities, ρ_c, of the proposed metallization are measured utilizing a transmission line model (TLM) method. Annealing at 360°C for 30 min yielded the lowest ρ_c of ~3.26×10^-5 Ω-cm² on 2×10¹³ cm^-3 n-GaAs with a Pd(300 Å)/Sn(1500 Å) contact. The EDAX spectra show a correlation between Ga signal peaks and measured ρ_c values at various annealing temperatures. The contact depth profiles are analyzed by SIMS. The effect of metallization thickness on contact properties are also presented. The mass spectrometer analysis confirms the formation of PdGa and SnGa compounds at the lowest ρ_c condition