Thermoelectric Effect in p-and n-type semi-conductors

When one end of a semi-conductor is hotter than the other, electrons leave the hot end and tend to flow to the cold end. The cold end soon becomes negatively charged with respect to the hot end. The negative charge at first increases till, owing to repulsion, the flow of electrons from the hot end is it equilibrium with the return flow from the cold end. The fewer the electrons available for the return flow the higher will be the voltage at the cold end, before equilibrium is reached. It is for this reason that thermoelectric power is much greater in a semiconductor than that of metals. Also the voltage difference between the hot and cold ends of a semi-conductor is set up not only by the flow of electrons but also by the flow of holes. In n-type semi-conductors the hot end is positive. In p-type the cold end is positive. In both types, however, the direction of electron flow is from the positive to the negative end. The flow of current in such a combination. Such the thermoelectric cell produces only 10th of the volt, and to obtain higher, a pile of such semi-electric is used. Such a thermoelectric generator is now widely used in supplying power to radio transmitters in rockets and satellites.


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