In semi-conductor, the carriers of current at room temperature are

1. Analyze the question It asks which charge carriers conduct current in a semiconductor at room temperature.

2. Explain the concept Semiconductors such as silicon and germanium have a small energy gap between the valence band and the conduction band.

• At absolute zero, the valence band is full and the conduction band is empty, so the material behaves as an insulator.
• At room temperature, thermal energy lets some valence electrons jump into the conduction band. These are free electrons.
• Each electron that leaves behind a vacancy called a hole, which acts as a positive charge carrier. Neighbouring electrons can move into the hole, so the hole appears to move in the opposite direction.

Both the electrons (negative carriers) and the holes (positive carriers) therefore contribute to the current.

3. Solution

• Electrons only (A): incomplete, because holes also carry current.
• Holes only (C): incomplete, because the free electrons also carry current.
• Electrons and ions (D): wrong, because ions in a solid lattice are fixed and do not carry current.
• Electrons and holes (B): correct.

4. Answer B. electrons and holes

5. Exam tip Remember this: "Metals use electrons; semiconductors use electrons AND holes." In an intrinsic (pure) semiconductor, the number of electrons equals the number of holes. In doped semiconductors, n-type has electrons as the majority carriers and p-type has holes as the majority carriers. Either way, both types of carrier are present.