CURRENT GAIN INCREASE IN ALGAAS GAAS HETEROJUNCTION BIPOLAR-TRANSISTORS USING ALGAAS LAYER OVERGROWTH/

Reduction of the surface recombination current components in Npn AlGaA s/GaAs heterojunction bipolar transistors has been achieved by overgro wing the emitter-mesas with an AlGaAs layer approximately 0.5 mum thic k. It was observed that the n = 2 recombination current was reduced by approximately 90%, to about 10% of the original value, with a corresp onding 13-fold increase in current gain for 270 X 20 mum2 devices. In addition, devices with the same emitter-base area, but significantly d ifferent perimeters, were observed to have similar current gains and n = 2 recombination current values. This was in contrast to devices fab ricated without an overgrowth layer. These results suggest that the ov ergrowth layer causes a very significant reduction in the perimeter re combination current.