C/sub BC/ reduction in GaInAs/InP buried metal heterojunction bipolar transistor

We fabricated GaInAs/InP based buried metal heterojunction bipolar transistors (BM-HBTs), in which a tungsten stripe with the same area as the emitter was buried with an intrinsic collector layer. In this device, there was no conductive layer under the extrinsic base region to reduce the total base-collector capacitance (C/sub BCT/). Though tungsten was embedded in an active region of HBTs, flat surface of base layer and no void formation around buried tungsten were confirmed by the observation of cross section. C/sub BCT/ of 10.3 fF was calculated from Y/sub 12/ parameters and an effective base-collector junction area of BM-HBT was estimated at 22% of conventional-HBT.