In semiconductor physics, what is meant by:
An amplifier,

Explanation

### Step-by-Step Solution:

1. **Definition of an Amplifier**:
An amplifier is an electronic device that increases the power of a signal. In semiconductor physics, amplifiers are typically realized using transistors.

2. **Structure of a Transistor**:
A transistor consists of three doped regions: the emitter, base, and collector. These regions form two p-n junctions.

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