Field-effect density modulation in Si nanowires for increasing ZT: A simulation study

Modulation doping is a promising way to increase the electronic conductivity of thermoelectric materials and achieve high ZT figure of merit. In this work we provide a qualitative and quantitative comparison of the thermoelectric performance of a fieldeffect density modulated Si nanowire channel of diameter D=12nm versus its doped counterpart. We employ self-consistent atomistic tight-binding simulations coupled to the Boltzmann transport equation. We describe the simulation model, and show that as a result of a large improvement in the electrical conductivity, gating, rather than doping, can provide improvements on the thermoelectric power factor larger than 3x. Despite the large increase in the electronic part of the thermal conductivity, the total thermal conductivity is still dominated by phonons. Thus, a ZT figure of merit more than 3x higher can be achieved in the gated channel compared to the doped channel as well. Finally, we show that similar to the case of doped channels, the power factor peak is obtained when the Fermi level resides ~kBT below the band edge.