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!