Novel doubly self-aligned AlGaAs/GaAs HBT

A novel, doubly self-aligned process technology for AlGaAs/GaAs heterojunction bipolar transistors (HBT) has been developed. This doubly self-aligned process enables self-alignment for all emitter, base, and collector contacts and the fabricated device occupies an area approaching the intrinsic device area. The resulting base-collector capacitance of a fabricated device is reduced below half of the base-collector capacitance of conventional devices. The reductions in the capacitance are reflected in the superior cutoff frequency and maximum oscillation frequency of the doubly self-aligned devices as compared with conventional devices.