Design and fabrication of submicrometer AlGaAs/GaAs HBTs grown by LPOMVPE

The device fabrication, high-frequency performance, and effects of a heavily-carbon-doped base on submicrometer AlGaAs/GaAs heterojunction bipolar transistors (HBTs) are discussed. Photoluminescence (PL) techniques were employed to study the contributions of surface and bulk recombination in GaAs:C samples. PL intensity was quenched mainly by the bulk recombination mechanism in heavily-carbon-doped samples. The contribution from surface recombination is negligible. The emitter size effect is eliminated by using a single p/sup +/ (1*10/sup 20/ cm/sup -3/) base layer in the HBT structure. Use of a heavily-carbon-doped base layer provides for low base resistance while maintaining the abrupt acceptor profile required for high emitter injection efficiency. A maximum frequency of oscillation (f/sub MAX/) of over 100 GHz has been obtained from a submicron HBT (0.6 mu m*8.5 mu m). As a result of minimizing surface recombination in the extrinsic base region, f/sub MAX/ increases from 70 GHz to 91 GHz as emitter width decreases from 3.0 mu m to 0.6 mu m (*4.5 mu m) while f/sub T/ remains nearly unchanged. The experimental results suggest that submicron AlGaAs/GaAs HBTs are suitable for ultra-high-speed IC applications.<
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