Lead telluride (PbTe) as well as lead tin telluride (Pb
Sn
Te) have
their operational temperature ranges between those of bismuth telluride and
silicon-germanium. Although the maximum figure of merit is slightly lower than
that of bismuth telluride, lead telluride extents the temperature range covered
for thermoelectric applications with comparable good efficiencies.
Electrical properties can be controlled by variations of the material
composition through changing the stoichiometric ratio. While excess usage of
lead results in an n-type semiconductor, a shift to more tellurium gives a
p-type semiconductor. However, the maximum carrier concentration achievable by
this mechanism is in the order of
, which is lower than
the ideal doping for thermoelectric applications [11]. Higher carrier
concentrations can be achieved by doping. While PbI
, PbBr
, or
Ge
Te
are used as extra donors, Na
Te or K
Te are applied for
elevating acceptor concentrations.
Both PbTe and Pb
Sn
Te can be manufactured as single crystals
as well as sintered materials. Sintered samples are usually fabricated at
temperatures around 1000
K [151] and are distinguished from
single crystals by their lower thermal and electrical conductivities due to
additional scattering at grain boundaries.
A comprehensive elaboration of the physical properties of lead telluride and lead tin telluride as well as according models for application within device simulation is given in Chapter 5.
M. Wagner: Simulation of Thermoelectric Devices