Periodic nanoslot patterns as an effective approach to improving the thermoelectric performance of thin films

For thermoelectric applications, thermoelectric Si thin films with periodic circular pores have been intensively studied because of the low price and earth abundance of Si. In this work, a different periodic nanoporous pattern is investigated for its potential thermoelectric benefit, i.e., a Si thin film with periodic nanoslots. Inside such structures, the neck between adjacent nanoslots functions as the nanorestriction to suppress the phonon transport, leading to a dramatically reduced lattice thermal conductivity. When the neck width is still longer than the mean free paths of majority charge carriers, bulklike electron transport can be maintained so that the thermoelectric ZT can be enhanced. For the thermal designs of these porous thin films, a simple but accurate analytical model based on the mean-free-path modification with a characteristic length is derived and is used to predict their thermoelectric properties. For heavily doped Si films with the neck width reduced to 5 nm, the computed ZT can reach 0.58 at 1100 K. The proposed nanoslot pattern can be extended to general thin films and atomic thick materials to tune their transport properties.