Abstract
The purpose of this research is to use a First Principles study in an effort to enhance the Figure of Merit of silicon nanowires. Nowadays, most of the constituents in thermoelectric materials are rare earth elements; however, those elements are usually too expensive for commercial applications. Silicon is the second most abundant element in the Earth’s crust that enables a relatively cost effective extraction and a sound availability, thus its low price. Moreover, silicon is an ideal material for compatibility with electronic technology. On the basis of the above, we focus on silicon nanowires and investigate its thermoelectric properties under different pressure conditions. The efficiency of thermoelectric materials will mainly be affected by the electrical conductivity, Seebeck coefficient, and thermal conductivity, etc. All these parameters will be inevitably influenced by changing the basic material properties which include; the band structure, band gap, density of state, to name a few. Theoretically, these material properties will also vary with different sizes, orientations and crystal structures (e.g., diamond structure for 1 atm. and beta-phase for 7.5~10.5GPa). Therefore, silicon cluster models in these different conditions were built and their transport properties employing a Density Functional Theory (DFT) approach were evaluated. Additionally, these silicon cluster models will be approximated to real nanowires for the sake of periodic crystal structures using periodic boundary conditions. This research is also concerned on the thermodynamic properties including; the phonon dispersion relation and phonon density of states, as well as specific heat. All these calculations are determined on the basis of the Density Functional Perturbation Theory (DFPT). Furthermore, using the Boltzmann transport equation will include a holistic sum of the previously calculated properties. As a result, key parameters concerning the figure of merit of thermoelectric materials of interest will be obtained. Finally, a comparison between the electric and thermal properties of both diamond and beta-phase Si NW structures will be conducted place in order to determine the structure with superior efficiency.