But their thermoelectric properties are still not up to the mark
for superior high temperature performance.
The dimensionless figure of merit ZT [1] provides the measure of the quality of a good thermoelectric material. It is defined as
where r is the electrical conductivity, j is thermal conductivity and S is the Seebeck coefficient. To achieve high ZT, increase in S and (or) r and decrease in j are
required. But for simple materials, increase in S leads to a decrease in r. Similarly, an increase in r is followed by an increase in j according to Wiedemann–Franz law. Hence,
ZT effectively remains more or less constant. To increase Z,various models have been proposed in the last decade.Amongst them, the most exciting proposal by Hicks et al.
[9,10] was superlattice quantum-well materials, having an effective two-dimensional density of states for carriers. This density of state is given by (m)/(ph¯2a), where m is the carrier
mass and a is the quantum-well width. These authors assumed infinite potential barrier with zero barrier width