Thermally stable WTiAu non-alloyed ohmic contacts on In 0.5Ga 0.5As for GaAsAlGaAs heterojunction bipolar transistor applications

Abstract

This paper demonstrates WTiAu as a thermally stable, low resistance, non-alloyed, emitter ohmic contact for GaAsAlGaAs heterojunction bipolar transistor applications. The minimum W layer thickness required for low contact resistance and long-term thermal stability was obtained. A W layer 900 Å thick yielded the lowest contact resistance ( R c = 0.045 ω mm ) with a high degree of uniformity after (1) a collector ohmic contact rapid thermal annealing cycle at 420 °C and (2) 500 h at 250 °C. Secondary ion mass spectroscopy results indicate that In outdiffusion contributes to the thermal instability when thinner W layers are used.