Enhancement of f/sub max/ in InP/InGaAs HBTs by selective MOCVD growth of heavily-doped extrinsic base regions

InP/InGaAs heterojunction bipolar transistors (HBT's) with selectively grown heavily-doped extrinsic base layers have been fabricated. A new selective metalorganic chemical vapor deposition (MOCVD) method using a very high-speed rotating susceptor, which can attain high selectivity even at low growth temperature, is employed for the extrinsic-base regrowth. The maximum f/sub max/ of the HBT with the selectively grown extrinsic-base layer is 141 GHz, which is more than 50% larger than that of a HBT without the selective growth. The base resistances are estimated by a small-signal equivalent-circuit analysis and transmission line model measurements, and we find that the resistance is reduced to be about a half by the selective regrowth. This significant reduction is achieved by the decrease of base contact resistance as well as the low regrowth-interface resistance. We also discuss Zn redistribution during the extrinsic base regrowth.