A collector-up heterojunction bipolar transistor using a p-type doping buried layer

In this paper, we report a collector-up npn heterojunction bipolar transistor (C-up HBT) which employs a p-type doping buried layer inserted between an extrinsic emitter and a subemitter for current confinement. Fabrication of C-up AlGaAs/GaAs HBTs with a selectively buried layer by metalorganic chemical vapour deposition (MOCVD) regrowth is described. The fabricated C-up AlGaAs/GaAs HBT demonstrates good common-emitter I-V characteristics and a current gain of 18. A systematic analysis is performed to verify the functionality of the p-type doping buried layer using a two-dimensional device simulator. It is found that the p-type doping buried layer should be biased properly to achieve the high efficiency of current confinement. And the HBT with a large ΔE_V at the base-emitter heterojunction is preferred for the proposed C-up HBTs to reduce hole back-injection.