Thermoelectric Transport in 2D and Layered Materials

Abstract

Thermoelectric materials are used for power generation and refrigeration (pumping of heat from cold side to hot side). They could also be used for electronic cooling, combining active and passive cooling to efficiently cool down hot spots of a chip. 2D materials could be used for all three operational modes. In the in-plane direction, usually their thermal conductivity is large and therefore they are more suitable for electronic cooling. In a recent work we have shown that graphene on hBN substrate demonstrates record high thermoelectric power factor of more than 10 W/mK at room temperatures. One can also use 2D modulation doping to create effective 2D transport at the surface of bulk materials. Modulation doping benefits from high mobility which could be used to achieve large thermoelectric power factor values. On the contrary, in the cross-plane direction, layered 2D materials are weakly bonded with van-der-Waals bonds and therefore they could have extremely low thermal conductivity values, making them potentially good candidates for traditional thermoelectric applications. We have shown such layered van-der-Waals structures could serve as efficient thermionic coolers/ power generators.