Question

What is the basic structure of BJT?

Answer 1

A **BJT (Bipolar Junction Transistor)** is a type of transistor used to amplify or switch electronic signals. It has three main parts:

1. **Emitter (E):** This is where the charge carriers (electrons or holes) are injected into the transistor. The emitter is always heavily doped (to allow easy movement of charge carriers).

2. **Base (B):** This is the middle part of the BJT, and it is lightly doped. The base controls the flow of charge carriers between the emitter and the collector. The current that flows into the base controls the larger current flowing from the emitter to the collector.

3. **Collector (C):** This is where the charge carriers flow out of the transistor. The collector is moderately doped and collects the charge carriers from the emitter.

### Types of BJTs:
- **NPN BJT:** The emitter is made of **n-type** material, while the base and collector are made of **p-type** material.
- **PNP BJT:** The emitter is made of **p-type** material, while the base and collector are made of **n-type** material.

### Structure Summary:
- **Emitter:** Highly doped (either n or p type depending on NPN or PNP).
- **Base:** Lightly doped, thin layer.
- **Collector:** Moderately doped.

In operation, a small current flowing into the base controls a much larger current flowing from the emitter to the collector. This makes the BJT useful for amplification or switching applications.