Base-collector capacitance reduction of AlGaAs/GaAs heterojunction bipolar transistors by deep ion implantation

In this paper we present a novel technique which can significantly reduce the base-collector capacitance (C/sub bc/) in AlGaAs/GaAs HBTs. C/sub bc/, is a key limiter of HBT microwave gain and bandwidth. Our process uses high dose, high-energy ion implantation through the external base layer to compensate part of the heavily doped sub-collector. It also uses the more conventional self-aligned shallow implant to compensate the entire collector underneath the base contact. The total C/sub bc/ of the double implanted HBTs has been reduced by more than 35% with this new technique as compared to devices with shallow implant only. Under proper conditions, the double implantation produces little damage to the base (which can cause an increase in base resistance R/sub B/); thus the RF performance can be significantly improved. An f/sub MAX/ greater than 200 GHz has been obtained, comparable to the best previous reported results in common emitter HBTs.