Suppression of the emitter size effect on the current gain of AlGaAs/GaAs heterojunction bipolar transistor by utilizing (NH4)2S<i>x</i> treatment

Abstract

The (NH4)2Sx surface treatment was applied to the AlGaAs/GaAs heterojunction bipolar transistor. The suppression of the emitter size effect on the current gain was observed for up to 4×4 μm2 emitter size devices, and 2.5 times high current gain was obtained with the improvement of the ideality factor. These results indicate that the surface recombination at emitter-base junction area are largely reduced by this treatment. The (NH4)2Sx treatment also proved to be applicable to the conventional device fabrication processes and highly reliable for the heat treatment.