Valence Band, Conduction Band and Forbidden Energy Gap скачать в хорошем качестве

Valence Band, Conduction Band and Forbidden Energy Gap

The atoms of a solid are arranged in a regular repeated geometric pattern and the electrons of the atom revolve around the nucleus in certain permitted energy levels. The electrons in the inner shells are strongly bound to the nucleus. A band which is occupied by the valence electrons or a band having highest energy is defined as valence band. The valence band may be partially or completely filled. This band can never be empty. In some materials, the valence electrons are loosely attached to the nucleus. Even at room temperature, some of the valence electrons can leave the valence band. These are called as free electrons. They are responsible for conduction of current in a conductor and are henceforth called as conduction electrons. The band occupied by these electrons is called conduction band. This band may be an empty band or partially filled band. The separation between valence band and conduction band is known as forbidden energy gap. If an electron is to be transfered from valence band to conduction band, external energy is required, which is equal to the forbidden energy gap.