AlGaAs/GaAs HBTs with reduced base-collector capacitance by using buried SiO/sub 2/ and polycrystalline GaAs in the extrinsic base and collector

A novel AlGaAs/GaAs HBT (heterojunction bipolar transistor) structure with buried SiO/sub 2/ and polycrystalline GaAs (poly-GaAs) in the extrinsic base and collector is presented. The lower dielectric constant of SiO/sub 2/ and complete carrier depletion of n-type poly-GaAs have reduced the extrinsic component of C/sub BC/ (base-collector capacitance) to 30% while f/sub T/ has been kept high by a thin intrinsic collector. By using newly developed low-resistance p-type poly-GaAs for the base electrode, further reduction in C/sub BC/ is expected with a one-dimensional transistor structure, such as SICOS.