There
are three kinds of effects based on the thermoelectric phenomenon,
namely Seebeck effect, Peltier effect,
and Thomson effect. The first thermoelectric generator was invented from the
Seebeck effect in 1820s. Typically in a junction composed of two different
materials, the charge carrier like electron or hole would transfer at the
interface due to different carrier concentrations. The diffusion of carrier
causes a diffusing potential at the junction, which hinders the further
diffusion through a drift current. Finally, a balance is achieved between the
diffusion current and drift current, forming an electric field in this
junction.
The
intensity of the field is dependent on temperature, so it can be used to
measure temperatures. Vice versa when connecting two materials into a circuit
with two junctions and generating a temperature gradient in the two junctions,
there will be a current through this circuit, which is called Seebeck effect.
The current direction depends on the intrinsic properties of materials that are
used to construct the junction and temperature gradient direction. Conversely,
when a current comes through these two junctions, a temperature difference in
the two junctions has been created, which is called Peltier effect. For a
thermoelectric device based on the Peltier effect, whether the heterojunction would absorb or emit heat
depends on the current direction and the used materials. Normally the
semiconductor heterojunction causes a high temperature difference which is
beneficial for thermoelectric conversion
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