Energy gap between valence band and conduction band of a semiconductor is approximately:

The correct option is 1 eV.

In solid-state physics, materials are classified into conductors, semiconductors, and insulators based on their electrical conductivity and the size of the energy gap (band gap) between their valence band and conduction band.

The valence band is the band of electron orbitals that electrons can jump out of when excited, while the conduction band is the band of electron orbitals that electrons can jump into, allowing them to flow and conduct electricity.

The energy gap, denoted as
$$E_g$$
is the energy difference between the top of the valence band and the bottom of the conduction band. Let's compare this gap across different materials:

1. Conductors (e.g., metals): The valence band and conduction band overlap, meaning the energy gap is effectively zero ($E_g\approx 0\text{eV}$). Electrons can move freely into the conduction band even at room temperature.
2. Semiconductors (e.g., Silicon, Germanium): The energy gap is small, typically around 1 eV. For example, the band gap of Silicon (Si) is approximately 1.1 eV and for Germanium (Ge) it is about 0.72 eV at room temperature. At 0 K, they behave as insulators, but at room temperature, a significant number of electrons gain enough thermal energy to cross this small gap into the conduction band.
3. Insulators (e.g., Diamond, Glass): The energy gap is very large, usually greater than 5 eV (and often around 10 eV or more). Under normal conditions, electrons cannot acquire enough energy to cross this wide gap.

Therefore, for a semiconductor, the energy gap between the valence band and conduction band is approximately 1 eV.