Formation of Bands

Show/Hide Sub-topics (Semiconductors | A Level Physics)

The states of electrons in an atom are described by quantum physics using four quantum numbers. The quantum numbers describes the allowable states electrons may assume in an atom.

When single atoms combine to form substances, the outermost shells, subshells, and orbitals merge, providing a greater number of available energy levels for electrons to assume. For example, when two atoms are brought closer together, the levels of the isolated atoms split into two. When 7 atoms come together, there will be 7 available energy levels for the electrons. When a large number of atoms exist in close proximity to each other, these available energy levels form a nearly continuous band wherein electrons may transition.

Band diagram

Conduction band is in the range of electron energy higher than that of the valence band, sufficient to make the electrons free to accelerate under the influence of an applied electric field and thus constitute an electric current.

Band gap is the energy difference between top of valence band and bottom of conduction band. It is also a range of energy in a solid where no electron states exist.

For metals,

  • conduction band is partially filled due to overlap
  • electrons may move to a higher level energy state with little or no additional energy imparted.
  • Hence, outer electrons are ‘free’ and ready to move upon the application of an external electric field.

For Insulators,

  • The band gap is very large.
  • Electrons cannot ‘leap’ from the valence band to the conduction band at room temperature.
  • Hence, valence electrons are “bounded” to their constituent atoms and cannot become mobile within the substance without a significant amount of imparted energy.

Back To Semiconductors (A Level Physics)

Back To A Level Physics Topic List

Mini Physics

As the Administrator of Mini Physics, I possess a BSc. (Hons) in Physics. I am committed to ensuring the accuracy and quality of the content on this site. If you encounter any inaccuracies or have suggestions for enhancements, I encourage you to contact us. Your support and feedback are invaluable to us. If you appreciate the resources available on this site, kindly consider recommending Mini Physics to your friends. Together, we can foster a community passionate about Physics and continuous learning.

Leave a Comment

This site uses Akismet to reduce spam. Learn how your comment data is processed.