BREAKDOWN SPEED CONSIDERATIONS IN ALGAAS/GAAS HETEROJUNCTION BIPOLAR-TRANSISTORS WITH SPECIAL COLLECTOR DESIGNS

The breakdown-speed tradeoffs of AlGaAs/GaAs HBT's with special collector designs are presented. Monte Carlo techniques and 1D 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-) and inverted field (p-) 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 (deltan+-n--deltap+) HBT's. Undoped collector HBT's (i-deltap+) operate finally best at low currents. Overall, the use of special collector structures does not always guarantee best speed-breakdown performance.