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.
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