Question

In a semiconductor, the energy gap between the valence band and the conduction band is nearly:

• A. 5 eV
• B. 1 eV
• C. 15 eV
• D. zero

Hint:

Semiconductors have a small forbidden gap near 1 eV; metals have zero and insulators have a large gap of several eV.

Answer 1

The Correct Option is B

Step 1: Ask what makes a semiconductor special.
A semiconductor conducts only a little at room temperature because a modest amount of thermal energy can push some electrons across the gap into the conduction band. This requires the gap to be small, but not zero.

Step 2: Estimate using thermal energy.
Room-temperature thermal energy is only about \(0.025\) eV, yet semiconductors show measurable conduction. A gap of roughly \(1\) eV is small enough that a few electrons cross it, matching observed behaviour.

Step 3: Contrast with the extremes.
If the gap were \(0\) eV the material would be a metal (always conducting); if it were \(5\) eV or more, almost no electrons could cross and it would be an insulator.

Step 4: Pick the value.
Therefore the characteristic semiconductor gap is about \(1\) eV (Si \(\approx 1.1\) eV, Ge \(\approx 0.7\) eV).
\[\boxed{E_g \approx 1\ \text{eV}}\]