Physics

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Author: search.filters.author.Woods, R.C.Subject: search.filters.subject.AIGaAs/GaAs heterojunction bipolar transistors

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    Current gain increase in AlGaAs/GaAs heterojunction bipolar transistors using AlGaAs layer overgrowth
    (Applied Physics Letters, 1994) Kalingamudali, S.R.D.; Wismayer, A.C.; Woods, R.C.; Roberts, J.S.
    Reduction of the surface recombination current components in Npn AlGaAs/GaAs heterojunction bipolar transistors has been achieved by overgrowing the emitter?mesas with an AlGaAs layer approximately 0.5 ?m thick. It was observed that the n=2 recombination current was reduced by ?90%, to about 10% of the original value, with a corresponding 13?fold increase in current gain for 270?20 ?m2 devices. In addition, devices with the same emitter?base area, but significantly different perimeters, were observed to have similar current gains and n=2 recombination current values. This was in contrast to devices fabricated without an overgrowth layer. These results suggest that the overgrowth layer causes a very significant reduction in the perimeter recombination current.
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    Recombination current reduction in AlGaAs/GaAs heterojunction bipolar transistors with polyimide deposition
    (Solid State Electronics, 1994) Kalingamudali, S.R.D.; Wismayer, A.C.; Woods, R.C.
    N-p-n AlGaAs/GaAs heterojunction bipolar transistors of various emitter-mesa diameters have been fabricated to examine the effects on the recombination current with polyimide deposition. The recombination current in these devices (when the ideality factor is close to 2) was proportional to the device perimeter before and after polyimide deposition. This suggests that the dominant component of the recombination current in these devices is the perimeter recombination current. A simple model was developed which allowed the contribution from the perimeter and bulk recombination currents to be calculated. The common-emitter d.c. current gains of these devices increased correspondingly as recombination current decreased due to the polyimide deposition.