Rapid thermal diffusion and ohmic contacts using zinc in GaAs and GaAlAs

Abstract

We report behavior of zinc diffusion and p-type ohmic contacts to GaAs and GaAlAs (aluminum mole fraction ∼0.3) by Zn3As2 as vapor source and zinc embedded in tungsten films as solid source using rapid thermal processing. Tungsten acts as an inert refractory metallurgy during the processing. The diffusion profiles show high surface concentrations (mid 10 19 cm-3 to low 1020 cm-3) and a diffusion profile in agreement with Tuck's model of substitutional-interstitial diffusion in the presence of vacancy nonequilibrium. Both GaAs and GaAlAs show excellent transport properties with mobilities of 75-100 and 40-60 cm2 V-1 s-1, respectively, at room temperature. Short-time (sub-12-s) diffusions lead to sub-1000-Å diffused contacts in the 650-900°C temperature range with contact resistances below a measurement accuracy of 5×10-7 Ω cm2. The contact technology has been demonstrated in heterostructure bipolar transistors and p-channel heterostructure field-effect transistors. It is an attractive alternative to conventional gold-based contact metallizations.