I'm learning about the construction of Peltier tiles from Wikpedia. However, some of the statements in the article are not at all clear.
Two unique semiconductors, one n-type and one p-type, are used because they need to have different electron densities. The semiconductors are placed thermally in parallel to each other and electrically in series and then joined with a thermally conducting plate on each side. When a voltage is applied to the free ends of the two semiconductors there is a flow of DC current across the junction of the semiconductors causing a temperature difference. The side with the cooling plate absorbs heat which is then moved to the other side of the device where the heat sink is. Thermoelectric Coolers, also abbreviated to TECs are typically connected side by side and sandwiched between two ceramic plates. The cooling ability of the total unit is then proportional to the number of TECs in it.
What does "thermally in parallel to each other and electrically in series" mean for semiconductors? Also, why should they be arranged in this fashion?
Why does flow of DC current across the junction of semiconductors cause a temperature difference? Which "junction" are they talking about?