Breakdown-speed considerations in AlGaAs/GaAs heterojunction bipolar transistors with special collector designs

The breakdown-speed tradeoffs of AlGaAs/GaAs HBTs with special collector designs are presented. Monte Carlo techniques and 1-D drift-diffusion modeling are used for speed and breakdown simulation, respectively. Base current reversal is indicative of breakdown and is used in conjunction with the (breakdown voltage/total transit time) figure of merit in order to set up HBT performance criteria. Conventional (n/sup -/) and inverted field (p/sup -/) collectors show a good speed-breakdown compromise over a limited collector current density. Equally good characteristics but over a broader current range can be obtained from collector launcher ( delta n/sup +/-n/sup -/- delta p/sup +/) HBTs. Undoped collector HBTs (i- delta p/sup +/) operate best at low currents. Overall, the use of special collector structures does not always guarantee the best speed-breakdown performance.<
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