Thermoelectric properties of different polymorphs of gallium phosphide; A first-principles study

Abstract

In this article, the thermoelectric properties of five different polymorphs of gallium phosphide (GaP) such zinc-blende (zb-GaP), wurtzite (wz-GaP), sphalerite (sp-GaP), Beryllium oxide (β-BeO-GaP), and Silicon carbide (SiC-GaP) have been reported in detail. In this regard, the prerequisite electronic structure calculations have been performed in the framework of density functional theory (DFT), whereas the results for thermoelectric properties have been obtained via Boltzmann transport theory (BTT). We found that these GaP polymorphs exhibit relatively higher electrical conductivity corresponding to holes as a result larger power factors (PFs) have been realized for n-type doping than p-type. The highest values of PF corresponding to n-type doping have been recorded as 27.492 × 1010 W/mK2s, 27.999 × 1010 W/mK2s, 29.491 × 1010 W/mK2s, 15.706 × 1010 W/mK2s, and 26.557 × 1010 W/mK2s respectively, for zb-GaP, wz-GaP, sp-GaP, β-BeO- GaP, and SiC-GaP. Moreover, their PF has been further enhanced by the increase in temperature. In contrast, the Seebeck coefficients (thermopowers) have been found relatively larger for p-type doping than n-type. The relatively large thermopowers and lower thermal conductivity for p-type doping have resulted in the enhancement of Figure-of-merit (zT) by holes rather than electrons. The highest zT values have been recorded as 0.997, 1.004, 0.998, 1.001, and 1.010 in the case of zb-GaP, wz-GaP, sp-GaP, β-BeO-GaP, and SiC-GaP respectively. Our study indicates the adequate potential of these different polymorphs of GaP for thermoelectric applications.