Thermoelectric properties of nanoporous Si

Improvements in thermoelectric (TE) materials could lead to efficient solid-state energy-conversion for environmentally benign power generation and refrigeration. This realization would require a large increase to $\sim 3$ in the thermoelectric figure of merit $ZT$ at room temperature. Recent experiments have shown promise for practical applications of TE materials such as Bi$_{2}$Te$_{3}$/Sb$_{2}$Te$_{3}$ superlattices and PbSeTe/PbTe quantum dot superlattices, yielding $ZT$ of $2.4$ and $1.3-1.6$, respectively. In addition, there have been recent attempts to use Si for TE pplications due to its structural simplicity and the possibility of utilizing existing Si-based manufacturing processes. In the present work, we report theoretical studies on thermoelectric properties of Si with periodically arranged nanometer-sized pores ({\it nanoporous Si}). Specifically, we calculate the electrical conductivity, Seebeck coefficient and figure of merit of nanoporous Si for a range of configurations using a combined {\it ab inito} electronic structure calculation and Boltzmann transport approach at room temperature. The results show a substantial increase in $ZT$ compared with that of bulk Si, similar to recent findings for $ZT$ in Si nanowires. Approaches for increasing $ZT$ further in this porous material will also be discussed.