Semiconductor is a class of solid whose conductivity increases with an increase in

Analysis

The question asks for the physical factor that causes an increase in the electrical conductivity of a semiconductor material.

Concept Explanation

In physics, materials are classified based on their electrical conductivity. Semiconductors (like Silicon and Germanium) have properties that fall between conductors (like copper) and insulators (like glass).

• Conductors: As temperature increases, the atoms in the metal lattice vibrate more, causing more collisions with electrons. This increases resistance and decreases conductivity.
• Semiconductors: At absolute zero, a semiconductor acts like an insulator because its valence band is full and its conduction band is empty. However, as the temperature increases, thermal energy is provided to the electrons. This energy allows electrons to break free from their covalent bonds and jump from the valence band to the conduction band.
• Result: The increase in the number of free charge carriers (electrons and holes) leads to a significant decrease in resistance, which means the conductivity increases.

Step-by-Step Solution

1. Identify the nature of semiconductors: Semiconductors rely on the excitation of electrons across a small energy gap (band gap).
2. Analyze the effect of temperature: When heat is applied, the thermal energy provides enough kinetic energy for electrons to overcome the band gap.
3. Relate to conductivity: Conductivity ($\sigma$) is directly proportional to the number of charge carriers. Since temperature increases the number of charge carriers in a semiconductor, it directly increases the conductivity.
4. Evaluate other options: Pressure, current, and voltage do not fundamentally change the intrinsic charge carrier concentration of a semiconductor in the same way temperature does.

Conclusion

The conductivity of a semiconductor is highly sensitive to temperature. As temperature rises, more charge carriers become available, making the material more conductive.

Exam Tip: Always remember the "Semiconductor Rule": Temperature Up, Resistance Down, Conductivity Up. This is the opposite of what happens in metallic conductors!