difference between Valence Band (VB) and conduction band

The valence band (VB) and the conduction band (CB) are two of the key energy bands in the electronic structure of materials, especially in semiconductors and insulators. Here are the main differences between them!

Valence Band (VB)

1. Occupancy: The valence band is the highest energy band that contains electrons at absolute zero temperature. It is filled with electrons, and each electron is associated with a specific atom or ion in the crystal lattice.

2. Energy Levels: The energy levels in the valence band represent the highest energy states that electrons can occupy while remaining bound to their respective atoms. These energy levels are lower in energy compared to those in the conduction band.

3. Electron Behavior: Electrons in the valence band are tightly bound to the atomic nuclei and are not free to move throughout the crystal. They are involved in chemical bonding and do not contribute significantly to electrical conductivity.

4. Role: The valence band is responsible for the chemical properties of the material, including its ability to form bonds and participate in chemical reactions.

Conduction Band (CB)

1. Occupancy: The conduction band is the lowest unoccupied energy band. It does not contain any electrons at absolute zero temperature. However, it can contain electrons when the material is excited by external energy sources (e.g., heat or light).

2. Energy Levels: The energy levels in the conduction band are higher than those in the valence band. Electrons in the conduction band are not strongly bound to specific atoms and are relatively free to move throughout the crystal.

3. Electron Behavior: Electrons in the conduction band are responsible for electrical conductivity. When an electron absorbs enough energy (e.g., from heat or light), it can transition from the valence band to the conduction band and become a free charge carrier, contributing to electrical current.

4. Role: The conduction band determines the material's electrical properties, such as its ability to conduct electricity. Materials with a small energy gap between the valence and conduction bands (small band gap) are typically good conductors or semiconductors, while those with a large energy gap (large band gap) are insulators.