High-performance AlGaAs/GaAs HBT's utilizing proton-implanted buried layers and highly doped base layers

Fabrication of AlGaAs/GaAs heterojunction bipolar transistors (HBT's) using a proton-implanted external collector layer and a highly doped base layer is presented. Influence of the proton implantation on base-collector junction characteristics is systematically investigated. At the optimized implantation condition, a buried semi-insulating layer beneath the external base is formed without deteriorating the junction current-voltage characteristics. In a fabricated HBT with 2 µm × 10 µm emitter size, a cutoff frequency f
T
of 50 GHz and a maximum oscillation frequency f
max
of 70 GHz have been achieved.