Low resistance, thermally stable Au/Pt/Ti/WSiN ohmic contacts on n(+)-InGaAs/n-GaAs layer systems

The electrical properties of the ohmic contact systems Au/Pt/Ti/WSiN and Au /Pt/ Ti to n(+)-InGaAs/GaAs layers grown by metalorganic vapor phase epitax y were investigated and compared to each other. The thermal stability prope rties of these contact systems were characterized by accelerated stress tes ts at elevated temperatures and by complementary thin film x-ray diffractio n analysis to evaluate the microstructural properties of degraded and nonde graded structures. The goal of these efforts was to develop stable, homogen eous emitter contacts for power heterojunction bipolar transistors. It was found that for both contact systems the best (specific) contact resistance R-c (rho(c)) is about 0.05 Omega mm (2 x 10(-7) Omega cm(2)) in the as-depo sited state. Au/Pt/Ti/WSiN contacts show no degradation after aging at 400 degrees C for more than 20 h. This is in contrast to standard Au/Pt/Ti cont acts which significantly degrade even after short time annealing at 400 deg rees C. The good long-time stability of the Au/Pt/Ti/WSiN system is related to the advantageous properties of the reactively sputtered WSiN barrier la yer.