  In the past decade, there has been significant interest in the potentially
advantageous thermoelectric properties of one-dimensional (1D) nanowires, but
it has been challenging to find high thermoelectric power factors based on 1D
effect in practice. Here we point out that there is an upper limit to the
thermoelectric power factor of non-ballistic 1D nanowires, as a consequence of
the recently established quantum bound of thermoelectric power output. We
experimentally test this limit in quasi-ballistic InAs nanowires by extracting
the maximum power factor of the first 1D subband through I-V characterization,
finding that the measured maximum power factors conform to the theoretical
limit. The established limit predicts that a competitive power factor, on the
order of mW/m-K^2, can be achieved by a single 1D electronic channel in
state-of-the-art semiconductor nanowires with small cross-section and high
crystal quality.
