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Unformatted text preview: 1 Preparing to compute I Preparing to compute I C 1D representation of HBT Biased in active mode Choose the base region in which to evaluate the electron current 2 Reduce our equation Reduce our equation set for the electron current set for the electron current in the base in the base What about Poisson? What about the recombination term? 3 Diffusion and Recombination in the base Diffusion and Recombination in the base 10 16 10 17 10 18 10 19 10 20 106 105 104 103 102 101 Doping (cm3 ) Diffusion length (cm) L e L h The equation set reduces to Results for L e for GaAs In modern HBTs W B /L e << 1 and is constant 4 Computing I Computing I C What is n E *? Diffusion (and no recombination) in the base: What are the BC's at x dp +W B ? 5 Collector current: controlling velocities Collector current: controlling velocities Substitute for the carrier concentrations at the boundaries1 Note: the reciprocal velocities inclusion of v R necessary in modern HBTs 6 Base current: components Base current: components (iv) Note V bi Which I B components do we need to consider? 7 Base current components and...
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 Fall '09
 David

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