Srd. Kalingamudali et al., CURRENT GAIN INCREASE IN ALGAAS GAAS HETEROJUNCTION BIPOLAR-TRANSISTORS USING ALGAAS LAYER OVERGROWTH/, Applied physics letters, 65(11), 1994, pp. 1403-1405
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.