Conduction mechanism of SnO2 semiconductors

[Foder]

Hello everybody and welcome to my first thread.

I have read several publications regarding this compound, and found that SnO2 behaves as n-type semiconductor (Eg 3.6 eV) when oxygen vacancies are present. Very summarized and simply put, I understood that this lack of oxygen atoms enhance the movility of the electrons (of the sorrounding Sn/O) which would interact with them (by 'them' I mean the absent oxygen atoms), allowing them to reach the conduction band when thermally activated, increasing the number of charge carriers. Wrong or rather not, my first request would be a better explanation of this, expanding what I have said or rather correcting it.

On a second plane, stoichiometric, defect-free SnO2 would be a normal insulator, with a high resistance value. Which would be the natural state of SnO2, insulator or semiconductor? I mean, the oxygen vacancies are natural or rather only attainable artificially when fabricating the crystal (on thin films, nanostructures, for example). What kind of SnO2 would I have, for example, in regular Ag/SnO2 contact materials (produced by powder metallurgy or internal oxidation)?

Thank you very much in advance.

 

[eljose79]

Thank you for your post and for your interest in SnO2. Your understanding of the behavior of SnO2 as a semiconductor is generally correct. Let me expand on it and address your questions.

Semiconductors are materials that have an energy gap between their valence band (where electrons are bound to atoms) and their conduction band (where electrons are free to move and conduct electricity). In a pure, defect-free SnO2 crystal, this energy gap is too large for electrons to easily jump from the valence band to the conduction band. This makes SnO2 a poor conductor and thus an insulator.

However, as you mentioned, when oxygen vacancies are present in the crystal, they can act as traps for electrons and allow them to move more easily from the valence band to the conduction band. This creates more charge carriers and increases the conductivity of the material, making it behave as a semiconductor. This is known as n-type doping, as the oxygen vacancies introduce extra negative charge carriers.

These oxygen vacancies can occur naturally in SnO2 crystals, but they are also intentionally created during the manufacturing process of certain applications, such as thin films or nanostructures. In regular Ag/SnO2 contact materials, the oxygen vacancies are also present due to the internal oxidation process used to produce them.

In summary, the natural state of SnO2 is as an insulator, but it can behave as a semiconductor when oxygen vacancies are present. The type of SnO2 you have in regular Ag/SnO2 contact materials would be a semiconductor due to the intentional introduction of oxygen vacancies.

I hope this helps clarify your understanding of SnO2. Please let me know if you have any further questions or would like me to expand on any points. Thank you for your interest in this topic.