The full form of CB VB, in the context of semiconductors and energy band diagrams, is Conduction Band Valence Band.
These terms are fundamental to understanding how semiconductors, conductors, and insulators behave. Let's break down what each term means:
Conduction Band (CB)
- The conduction band is the energy band that represents the range of energy levels that electrons must occupy to be free to move within a solid material.
- Electrons in the conduction band can easily move and contribute to electrical current.
- In conductors, the conduction band is partially filled, allowing for easy electron flow.
- In semiconductors, the conduction band is mostly empty, but electrons can be excited into it by thermal energy or other means, enabling conductivity.
- In insulators, the conduction band is far removed in energy from the filled valence band, requiring a great amount of energy for electrons to reach the conduction band, so it doesn't readily conduct.
Valence Band (VB)
- The valence band is the energy band containing the valence electrons of the atoms that make up the solid.
- Valence electrons are the outermost electrons of an atom, and they are responsible for chemical bonding.
- The valence band is usually mostly filled with electrons at absolute zero temperature.
- Electrons in the valence band are typically bound to atoms and do not contribute significantly to electrical current unless they are excited to the conduction band or "holes" are created.
- The highest energy level of the valence band is called the valence band maximum.
The relationship between the conduction band and valence band, specifically the energy gap between them (the band gap), determines the electrical conductivity of a material. A small band gap allows electrons to easily move to the conduction band (semiconductors), while a large band gap prevents this (insulators). Conductors have overlapping conduction and valence bands.
