Thermalization and recombination when donors are present

[BeauGeste]

Ok, let's say you have n-type impurities in a semiconductor. So there is an equilibrium number of electrons in the conduction and impurity bands given by the temperature and the typical semiconductor statistics.

Now, you excite electrons from the valence to the conduction band. Here are my questions:

1. Will some of the resultant recombination be impurity band to valence band? (Assume low temperatures and small binding energy if you must).

2. Will some conduction electrons that have not yet recombined into the valence band, thermalize into the impurity band (that has some vacancies due to donor electrons recombining).

I have read a lot on semiconductors but I have not seen anyone discuss if this occurs yet I have been told that it is true.
Thanks.

 

[BigJDubs]

Yes, some of the recombination will be from the impurity band to the valence band. This is known as Auger recombination, and is caused by electrons in the conduction band colliding with electrons in the impurity band and transferring their energy into the lattice. Yes, some of the conduction electrons will thermalize into the impurity band. This is known as impact ionization, and is caused by electrons in the conduction band colliding with electrons in the impurity band and transferring their energy into the impurity band, creating vacancies.

 

[charng]

I can confirm that both thermalization and recombination can occur when donors are present in a semiconductor. In fact, these processes are essential for understanding the behavior of semiconductors.

Thermalization refers to the process by which electrons in the conduction band reach thermal equilibrium with the surrounding lattice. This occurs through interactions with phonons (lattice vibrations) and other electrons. When donors are present, these interactions can also occur with the impurity band, leading to thermalization of conduction electrons into the impurity band.

Recombination, on the other hand, is the process by which an electron in the conduction band recombines with a hole (a positively charged vacancy) in the valence band, resulting in the release of energy in the form of a photon. This process can also occur between the impurity band and the valence band, as long as there is a sufficient number of vacancies in the impurity band.

So to answer your questions specifically:

1. Yes, it is possible for recombination to occur between the impurity band and the valence band, as long as there are vacancies in the impurity band and the binding energy is small enough to allow for the recombination process.

2. Similarly, it is possible for conduction electrons to thermalize into the impurity band when there are vacancies due to donor electrons recombining. This can happen at low temperatures, when the thermal energy is not enough to overcome the binding energy of the donor electrons.

While these processes may not always be explicitly mentioned in discussions about semiconductors, they are certainly important and can have significant effects on the behavior of these materials. I hope this helps to clarify any confusion you may have had.