  We present a model for P-N-P abrupt heterostructures vertical to temperature
gradient to improve the thermoelectric performance. The P-N-P heterostructure
is considered as an abrupt bipolar junction transistor due to an externally
applied temperature gradient paralleled to depletion layers. Taking Bi2Te3 and
Bi0.5Sb1.5Te3 as N-type and P-type thermoelectric materials respectively for
example, we achieve the purpose of controlling the Seebeck coefficient and the
electrical conductivity independently while amplifying operation power. The
calculated results show that the Seebeck coefficient can reach 3312V/K, and the
ZTmax values of this model are 45 or 425, which are tens or even hundreds of
times greater than those of bulk materials and films.
