What is true about semiconductors?

What is true about semiconductors?

• A. Semiconductors - pure state are insulators; impurities enable conduction; silicon and germanium examples.
• B. They always conduct like metals.
• C. They are always insulators.
• D. They cannot be doped.

Answer: (A)

The question tests how conductivity in semiconductors depends on purity and impurities. In an intrinsic (pure) semiconductor, there are very few free charge carriers at room temperature, so it behaves almost like an insulator. Introducing impurities—doping—adds extra energy levels within the band gap that make it easier for electrons to jump into the conduction band or for holes to form in the valence band. These additional carriers dramatically increase conductivity. Silicon and germanium are classic examples because they can be doped to create well-controlled n-type (more electrons) or p-type (more holes) materials. This ability to tune conduction with dopants is what makes semiconductors unique, unlike metals that conduct due to their partially filled bands regardless of impurities, or insulators that resist conduction even with small perturbations. Dopants can be added to semiconductors, so the statement that pure form is insulating and impurities enable conduction, with silicon and germanium as examples, is the accurate description.

The question tests how conductivity in semiconductors depends on purity and impurities. In an intrinsic (pure) semiconductor, there are very few free charge carriers at room temperature, so it behaves almost like an insulator. Introducing impurities—doping—adds extra energy levels within the band gap that make it easier for electrons to jump into the conduction band or for holes to form in the valence band. These additional carriers dramatically increase conductivity. Silicon and germanium are classic examples because they can be doped to create well-controlled n-type (more electrons) or p-type (more holes) materials. This ability to tune conduction with dopants is what makes semiconductors unique, unlike metals that conduct due to their partially filled bands regardless of impurities, or insulators that resist conduction even with small perturbations. Dopants can be added to semiconductors, so the statement that pure form is insulating and impurities enable conduction, with silicon and germanium as examples, is the accurate description.