  The thermoelectric efficiency of semiconductors is usually considered in the
ohmic electronic transport regime, which is achieved through high doping. Here
we consider the opposite regime of low doping where the current-voltage
characteristics are nonlinear and dominated by space-charge-limited transport.
We show that in this regime, the thermoelectric efficiency can be described by
a single figure of merit, in analogy with the ohmic case. Efficiencies for
bulk, thin film, and nanowire materials are discussed, and it is proposed that
nanowires are the most promising to take advantage of space-charge-limited
transport for thermoelectrics.
