(published on 08/04/2012)
(published on 08/05/2012)
Nice questions. Let's have a first crack at them, then you can come back for more clarification. Notice that in that image you cited (below) the electrons flow from hot to cold. So do the holes. The arrows in the circuit show the direction of current flow, which is the same as the hole-flow direction and opposite to the electron flow direction, because it happens that historically the electron charge got defined as negative.
"Thermoelectric Generator Diagram" by Ken Brazier - self-made, based on w:Image:ThermoelectricPowerGen.jpg by CM Cullen (which is GFDL 1.2 and CC-by 2.5 licensed). Licensed under GFDL via Wikimedia Commons - https://commons.wikimedia.org/wiki/File:Thermoelectric_Generator_Diagram.svg#mediaviewer/File:Thermoelectric_Generator_Diagram.svg
If the two parts (n and p) were separate, then the temperature difference would drive electrons to the cold end of the n part until the ordinary electrical potential between hot and cold ends in each becomes big enough to drive an equal current back the other way. The same thing happens with holes in the p part. The hot-to-cold electrical potentials in the n and p parts then have opposite signs, since it takes opposite signs of potential to drive negatively charged electrons and positively charged holes back toward the hot end. That's just what you figured out.
Now when you connect that external circuit, the simple electrical potential differences will cause electrons to flow in that circuit, assuming it's made of typical conductors. I think that's the process you describe as "the valence electron and hole trying to find each other through the mutual conductive connection". Electrons arriving at the cold side of the p region do allow electron-hole recombination to occur there.
Here's another way to help think of it. Although entropy (S) isn't a conserved quantity, it can still flow around. The entropy flow will be from hot to cold. In the n part, the electrons are the thing that carries the entropy. In the p part, the holes carry the entropy.
I hope that helps your son get started.
(published on 03/05/2015)
Thanks for the note! The wiki images are a huge help in explainig things like this. We should use them more often.
p.s. Here's another old answer that might have something useful for you guys: .
(published on 03/06/2015)