Consider an uniformly doped BJT, let Ne, Nb and Nc represent the emitter, base and collector doping in atoms / cm3 respectively. If the emitter injection efficiency of the BJT is close to unity which one of the options is true?
 Ne=Nb and Nb<Nc
 Ne=Nb=Nb
 Ne>>Nb and Nb>Nc
 Ne<Nb<Nc

In a Bipolar Junction Transistor (BJT), emitter injection efficiency is a measure of how effectively the emitter injects carriers (electrons in an NPN transistor or holes in a PNP transistor) compared to the base. The emitter injection efficiency (\( \gamma \)) is defined as:

\[
\gamma = \frac{\text{current injected by the emitter}}{\text{total current entering the base-emitter junction}} = \frac{I_E}{I_E + I_B}
\]

For the emitter injection efficiency to be close to unity (\( \gamma \approx 1 \)), most of the carriers must be injected by the emitter, and only a small portion of carriers should come from the base. This implies the following:

- The emitter should be much more heavily doped than the base, i.e., \( N_E >> N_B \), to ensure that a higher number of carriers are injected from the emitter into the base.
- The base should be lightly doped compared to the emitter to avoid recombination in the base.
- The collector's doping level is usually less than that of the base to facilitate easy collection of carriers, i.e., \( N_C < N_B \).

Given this information, the correct answer is:

**Ne >> Nb and Nb > Nc**

This corresponds to the third option:  
**Ne >> Nb and Nb > Nc**

### Do you want details or have any questions?

Here are 5 related questions to deepen your understanding:
1. How does base width affect the base transport factor in a BJT?
2. What is the relationship between doping concentration and breakdown voltage in a BJT?
3. How does emitter doping affect the forward current gain in a BJT?
4. Why is the base typically lightly doped in a BJT?
5. What factors affect the common-emitter current gain (\( \beta \)) of a BJT?

**Tip:** A higher emitter doping concentration reduces recombination in the base, improving efficiency and current gain in a BJT.

Consider a uniformly doped BJT, let Ne, Nb, and Nc represent the emitter, base, and collector doping in atoms/cm³ respectively. If the emitter injection efficiency of the BJT is close to unity which one of the options is true?

Ne=Nb and Nb<Nc
Ne=Nb=Nb
Ne>>Nb and Nb>Nc
Ne<Nb<Nc

Explore how the emitter injection efficiency in a BJT depends on doping concentrations. This problem focuses on semiconductor physics concepts, using the formula for emitter efficiency and explaining the relationship between emitter, base, and collector doping levels. Ideal for university-level electronics students.

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