Self-aligned AlGaAs/InGaAs/GaAs collector-up heterojunction bipolar transistors for microwave applications

The authors discuss the recent development of high-performance AlGaAs/InGaAs/GaAs collector-up HBTs (heterojunction bipolar transistors) fabricated by using a novel self-aligned base/collector process. Transistors with collector widths down to 2.6 mu m and base doping up to 1*10/sup 20//cm/sup 3/ have been fabricated and tested. Based on s-parameters measured up to 26 GHz, an extrapolated current gain bandwidth, f/sub t/, of 65 GHz and a maximum frequency of oscillation, f/sub max/, of 102 GHz have been obtained. To the authors' knowledge, these are the first C-up HBTs demonstrated to operate at or above microwave frequencies.