Silicon: Potential Thermoelectric Material?

The figure of merit of thermoelectric material is determined by electrical and thermal conductivities and the Seebeck coefficient. Silicon can have relatively high electrical conductivity and Seebeck coefficient but the use of silicon in thermoelectric applications has been plagued be the high thermal conductivity of the lattice, leading to figure of merit values about 0.01 at room temperature. However, silicon, being the major semiconductor material and having extremely well developed processing technology, would be very attractive material also for thermoelectrics. Recently it has been shown that by reducing the dimensions the thermal conductivity can be largely reduced. Thermal conductivity of ~1 W/mK has been reported for silicon nanowires, leading to figure of merit of 0.6 at room temperature.1 Reduction of thermal conductivity by a factor of 20 compared to bulk value has been measured in free-standing silicon membranes with thickness below 10 nm.2,3 These values together with the still high electrical conductivity and Seebeck coefficient suggest that nanoscale silicon structures can provide relatively high figure of merit and prove to be useful for thermoelectrics applications. In this talk we will discuss the performance and potential of silicon membranes in thermoelectric generators and coolers and show that there is indeed promise and room for silicon devices.