High-f/sub max/ AlGaAs/InGaAs and AlGaAs/GaAs HBT's with p/sup +//p regrown base contacts

The present paper describes a new approach to fabricating high performance HBT's with low base resistance. Their base contact resistance is reduced by using MOMBE selective growth in the extrinsic base region-a key process in the fabrication of high-f/sub max/ AlGaAs/InGaAs and AlGaAs/GaAs HBT's. A p/sup +//p regrown base structure, which consists of a 40-nm-thick graded InGaAs strained layer and a heavily C-doped regrown contact layer, is used for the AlGaAs/InGaAs HBT's to reduce both their base transit time and base resistance, while preventing aluminum oxide incorporation at the regrowth interface. An h/sub fe/ of 93, an f/sub T/ of 102 GHz, and an f/sub max/ of 224 GHz are achieved for a 1.6-/spl mu/m/spl times/4.6-/spl mu/m HBT, together with reduced base push-out effects and improved reliability. AlGaAs/GaAs HBT's with an 80-nm-thick uniform base layer that have high f/sub max/ values ranging from 140-216 GHz are also fabricated using the selective growth technique. These results confirm the high potential of the proposed HBT's, especially for microwave and millimeter-wave applications.<>