Dissimilar thermoelectric P-N junction materials

[Science99]

Hi,
I had a question about p-n junctions. I've only recently started to learn these concepts so there may be flaws in my thinking (please feel free to correct me). What I'm understanding is that for a p-n junction to function properly and produce a current when connected with a load across the cold side, is that there has to be free holes and free electrons in the p-type and n-type materials, respectively. Doesn't this mean that any two p-type and n-type materials can be connected in conjunction to function according to the Seebeck Effect and generate electricity? But contrary to this, I see TE modules always being composed on ONE material that is doped to produce n and p-type. What is that makes the n and p-type materials in the same junction compatible with each other and able to generate electricity? Is it their carrier mobility or carrier concentration? Does it have to do with the temperature that they operate in? I would really appreciate any insight!

 

[eljose79]

Hi there,

Thank you for your question about p-n junctions. Your understanding is partially correct - for a p-n junction to function properly and produce a current, there do need to be free holes and free electrons present in the p-type and n-type materials, respectively. However, it is not as simple as connecting any two p-type and n-type materials together.

The reason for this is because the p-type and n-type materials must be carefully chosen and prepared in order to have compatible carrier mobility and concentration. Carrier mobility refers to how easily the electrons or holes can move through the material, while carrier concentration refers to how many free electrons or holes are present in the material. If these properties are not well-matched, the junction will not function efficiently and may not produce any current at all.

Additionally, the temperature at which the p-n junction operates can also affect its efficiency. In general, higher temperatures can result in higher carrier concentrations, which can increase the current produced by the junction. However, if the temperature gets too high, the materials may become too conductive and the efficiency of the junction may decrease.

As for why TE modules are composed of one material that is doped to produce both n and p-type regions, this is because it allows for better control and optimization of the carrier mobility and concentration in the material. By carefully doping one material, engineers can create a p-n junction with the desired properties for efficient electricity generation.

I hope this helps to clarify your understanding of p-n junctions and their operation. Please let me know if you have any other questions.