Effect of emitter-base spacing on the current gain of AlGaAs/GaAs heterojunction bipolar transistors

An investigation of the effect of surface recombination and emitter-base-contact spacing on the DC current-gain of AlGaAs/GaAs heterojunction bipolar transistor (HBT) using thin AlGaAs emitter structures is discussed. The selectively-etched, thin-AlGaAs-emitter layer has been used to prevent an exposed extrinsic base region, which has previously limited current gain because of high surface recombination. It is found that a factor of approximately 50 improvement in the current gain can be achieved by proper surface passivation and emitter-base-contact spacing.>