Question

Which of the following best describes the band structure of intrinsic silicon?

• A. Single energy band
• B. Completely overlapping conduction and valence bands
• C. A wide band gap between the conduction and the valence bands
• D. No conduction band

Hint:

Semiconductors like Silicon have a distinct energy gap (\(E_g \approx 1.12\text{ eV}\)). Conductors show overlapping bands, while insulators have an extremely wide gap (\(E_g > 5\text{ eV}\)).

Answer 1

The Correct Option is C

Understanding the Concept: According to solid-state band theory, the electronic energy states of a crystalline solid are organized into distinct energy bands separated by forbidden energy gaps:
• Valence Band: The band of energy states containing the valence or outer-shell electrons of the host atoms.
• Conduction Band: The higher-energy band containing free, mobile charge carriers capable of moving under an electric field to support electric current conduction.
• Energy Band Gap (\(E_g\)): The forbidden energy spacing situated between the peak of the valence band and the base of the conduction band.

Step 1: Evaluating the semiconductor properties of Silicon.
Silicon (Si) is a group-IV element that behaves as a classic semiconductor. At absolute zero temperature (\(0\text{ K}\)), all its valence states are entirely occupied, and its conduction states are completely empty. It possesses a distinct, moderate forbidden energy band gap separating these two regions. For intrinsic silicon at room temperature (\(300\text{ K}\)), this energy gap is approximately \(1.12\text{ eV}\).

Step 2: Differentiating from conductors and insulators.
In structural metals (conductors), the valence and conduction bands overlap completely, making charge movement instantaneous without energy input. In pure insulators, the band gap is extremely large (often exceeding \(5\text{ eV}\)). For semiconductors like silicon, a well-defined gap exists, but it is small enough that thermal energy can excite electrons across it. Among the provided choices, describing this as a distinct band gap separating the conduction and valence regions perfectly matches Option (C).