Investigations of thermoelectric properties of different gallium nitride polytypes through first-principles approach

In recent years, exploring new polytypes of III-V semiconductors has been widely practiced for the development of thermoelectric devices of high efficiency. In this work, the thermoelectric properties of new polytypes, namely the wurtzite(wz), Berrylium oxide (β-BeO), Nickel arsenide (NiAs), Silicon carbide (SiC), and Titanium arsenide (TiAs) phases of GaN have been investigated using the first-principles approaches. It is found that the p-type of doping induces enhancement of the power factors (PFs) and figure-of-merits (zT) of the GaN polytypes. The optimal p-type doping for PFs has been recognized as −1.67 eV for wz-GaN, −1.78 eV for β-BeO-GaN, −1.33 eV for NiAs-GaN, −1.58 eV for SiC-GaN, and −1.48 eV for TiAs-GaN. These optimal p-type doping has induced the room-temperature PFs as high as 13.75 × 10¹⁰ W/mK²s recorded for wz-GaN, 13.61 × 10¹⁰ W/mK²s for β-BeO-GaN, 41.14 × 10¹⁰ W/mK²s for NiAs-GaN, 14.06 × 10¹⁰ W/mK²s for SiC-GaN, and 49.21 × 10¹⁰ W/mK²s for TiAs-GaN. Furthermore, the PFs of the GaN polytypes are enhanced by increasing the temperature. Due to such significant PFs, the zT values corresponding to p-type doping have been recorded as 1.013 for wz-GaN, 0.998 for β-BeO-GaN, 1.00 for NiAs-GaN, 1.015 for SiC-GaN, and 0.999 for TiAs-GaN. Moreover, we comprehensively discussed the electrical and thermal conductivities and Seebeck coefficients (S) for the predicted GaN polytypes. The results of the thermoelectric properties presented in this study reveal the predicted GaN polytypes may find interesting applications in thermoelectric devices for clean energy harvesting.