High-fmax AlGaAs/InGaAs and AlGaAs/GaAs HBT´s with p+/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_max AlGaAs/InGaAs and AlGaAs/GaAs HBT´s. A p⁺/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_fe of 93, an f_T of 102 GHz, and an f_max of 224 GHz are achieved for a 1.6-μm×4.6-μm 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_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.