Collector-up AlGaAs/GaAs heterojunction bipolartransistorsusing oxidised AlAs for current confinement

Abstract
The authors describe a novel method for fabricating collector-up AlGaAs/GaAs heterojunction bipolar transistors. An AlAs layer is inserted into the emitter layer and is oxidised in water vapour at 450°C. The resulting AlAs-oxide serves as a current confining layer that constricts collector current flow to the intrinsic portion of the device. DC devices with typical current gains of 50 are observed.