High Gain Npn AlGaAs/GaAs Heterojunction Bipolar Transistors Prepared by Molecular Beam Epitaxy

The behavior of surface recombination current in AlGaAs/GaAs heterojunction bipolar transistors prepared by molecular beam epitaxy have been investigated. By using compositional grading of the emitter-base junction and emitter edge-thinning design, the 1-kT injection current can be increased whereas the surface recombination current is suppressed at the same time. Consequently, the maximum differential current gain reaches 4200 which, to our knowledge, is the highest reported to date for AlGaAs/GaAs heterojunction bipolar transistors prepared by molecular beam epitaxy. © 1992 IOP Publishing Ltd.