A GaInP/GaAs HBT with a selective buried sub-collector layer grown by MOCVD

Summary form only given. Extrinsic base-collector capacitance under the base ohmic contact region is often a large portion of the total collector capacitance which degrades the RF performance for HBTs. We present a method to reduce the extrinsic base-collector capacitance for HBT using a selective buried sub-collector (SBSC) layer. A 4000/spl Aring/ sub-collector layer is first grown on a SI GaAs substrate followed by chemical etching to form a sub-collector mesa. By choosing proper etchant, the sub-collector mesa has the shape of a trapezoid. The HBT structure is then regrown starting from the lightly doped collector layer to the emitter cap layer. Normal HBT processing is then employed. The emitter is aligned with the subcollector and the base contact region is formed on the lightly doped collector layer above the SI GaAs substrate. The collector layer under the base contact region is depleted under bias so that the extrinsic base-collector capacitance is substantially reduced. An experimental carbon-doped GaInP/GaAs HBT with SBSC grown by IMOCVD was fabricated and compared with a normal HBT.