P-n junction in a thermoelectric device

[dumbchemist]

Greetings,

I've just learned some of the basics about thermoelectrics, and I often come across a diagram that confuses me (see the third and fourth figures in the http://en.wikipedia.org/wiki/Thermoelectric_effect#Charge-carrier_diffusion"). All of the literature I've read refers to the top connection between the n- and p-type as a p-n junction, but physically, there's a conductor connecting the p- and n-type materials (as shown in the diagram). How does this conductor effect the physics behind power generation? Qualitatively, I'd imagine one must choose a conductor having a Fermi level in between those of the p- and n-type materials - otherwise, migration would drive carriers toward the junction, opposing the temperature-induced current on one or the other side.

But in any case, I don't see how the junction can be referred to as a p-n junction, as it often is in the literature.

I'd appreciate any insight you might have on the subject! Thank you very much.

 

[eljose79]

Thank you for bringing up this interesting question about thermoelectrics. The diagram you referenced is indeed confusing, but let me clarify the role of the conductor in the thermoelectric device.

First, it is important to understand that a p-n junction is a type of interface between two different types of semiconductors, where one type has an excess of positive charge carriers (p-type) and the other has an excess of negative charge carriers (n-type). This junction is crucial for the thermoelectric effect, as it allows for the diffusion of charge carriers from one side to the other, creating a voltage difference across the junction.

Now, in the diagram you referenced, the conductor connecting the p- and n-type materials is not a separate component, but rather a part of the p-type material. This is known as a p-type conductor, where the material has a higher concentration of positive charge carriers compared to the n-type material. This conductor helps to balance out the charge carriers on either side of the junction, allowing for a more efficient diffusion of charge carriers and thus a larger voltage difference.

In terms of the Fermi level, you are correct in your assumption that it should lie in between the Fermi levels of the p- and n-type materials. This ensures that there is no net migration of carriers towards the junction, as this would oppose the temperature-induced current and decrease the efficiency of the device.

In summary, while the conductor in the diagram may seem confusing, it is actually an integral part of the p-type material and helps to optimize the thermoelectric effect. I hope this helps to clarify any confusion and please feel free to ask any further questions. Thank you for your interest in thermoelectrics!