Which of the following action would reduce the hole injection current from the base to the emitter of a NPN transistor (IEp in the given figure)?

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BlackTom AI · Accepted Answer

Let's break down what affects the hole injection current I_Ep (holes moving from base to emitter) in an NPN transistor.

Option 1: Increase base doping by 10x. If we increase the base doping (p-type concentration), there are more holes available in the base material. This tends to increase the supply of holes that can be injected into the emitter, which would not reduce I_Ep; in fact it could increase hole injection. Therefore this option would not reduce the hole injection current.

Option 2: Increase emitter doping by 10x. Higher emitter doping (n-type) increases the electron concentration in the emitter, which enhances electron injection into the base and can improve overall current gain, but it does not directly suppress the hole flow from base to emitter. The hole current I_Ep is primarily governed by base hole concentration and the base-emitter junction properties, so simply increasing emitter doping is unlikely to reduce I_Ep. This choice does not reliably reduce hole injection.

Option 3: Reduce base doping to 10%. Lowering the base doping means there are fewer holes in the base region to begin with. With fewer holes available to inject into the emitter, the hole injection component I_Ep would decrease. This directly targets the source of the hole current and is a plausible way to reduce it.

Option 4: Reduce emitter doping to 10%. Reducing emitter doping increases the contrast between emitter and base carrier concentrations, but it primarily affects electron injection and minority carrier behavior in the emitter. It does not directly reduce the hole injection from base to emitter; in fact, it might indirectly alter junction characteristics in ways that do not guarantee a reduction of I_Ep. This option is not the most direct or reliable method to lower the base-to-emitter hole current.

In summary, the most straightforward and effective way to reduce the hole injection current from base to emitter is to lower the base doping level, since that reduces the available base holes that can be injected into the emitter. The other options either increase hole availability or do not directly address the hole flux across the base-emitter junction.

EESM5200 (L2) Part I: Topic 11 - Basic BJT in Forward Active Mode

Which of the following action would reduce the hole injection current from the base to the emitter of a NPN transistor (IEp in the given figure)?

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