BJT practice problems
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An ideal, uniformly doped silicon npn transistor has the following doping and widths.
| NPN | emitter | base | collector |
| doping | NDE = 1.75e+18 cm-3 | NAB = 7.0e+16 cm-3 | NDC = 4.67e+15 cm-3 |
| widths | WE = 5 μm | WB = 2.5 μm | WC = 4 μm |
The BJT area is 200 μm x 200 μm.
Calculate βF and IS for the BJT.
If the BJT is biased in forward active operation, with VBE = 0.85 V, calculate the base, collector, and emitter currents, assuming room temperature operation.
Note: For silicon,
- the intrinsic carrier concentration is ni = 6.0e+9 cm-3
- the electron diffusion coefficient is 35 cm2/s, and
- the hole diffusion coefficient is 10 cm2/s.