Highly Thermoelectric Efficient Armchair Silicene Nanoribbons With Silicon Adatom Defects

Abstract

In this work, we propose armchair silicene nanoribbons with silicon (Si) adatom defect (ASiNR-Ad) for efficient thermoelectric devices. Using density functional theory (DFT) and nonequilibrium Green’s function method, we investigated the spin caloritronic effect on ASiNR-Ad of different widths ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${N}={4}$ </tex-math></inline-formula> , 5, 6, and 7). We observed that all ASiNR-Ads are magnetic semiconductors with a variable spin gap. Our results showed that the presence of adatom defect on armchair silicene nanoribbons (ASiNRs) significantly lowers phonon thermal conductance at ambient temperature. The ASiNR-Ads also exhibit large spin and charge Seebeck coefficient ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${S}_{s}$ </tex-math></inline-formula> and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${S}_{c}$ </tex-math></inline-formula> ) values of 1200 and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$1120 ~\mu \text{V}$ </tex-math></inline-formula> /K, respectively. The large value of Seebeck coefficients and reduced phonon thermal conductance results in the high value of spin and charge thermoelectric figure of merit ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${Z}_{s}{T}$ </tex-math></inline-formula> and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${Z}_{c}{T}$ </tex-math></inline-formula> ) of ~64 and ~58, respectively, in the narrow device which is substantially higher than pristine ASiNRs having a <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${Z}_{s}{T}={0}$ </tex-math></inline-formula> and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${Z}_{c}{T}={2.8}$ </tex-math></inline-formula> . Spin current ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${I}_{s}$ </tex-math></inline-formula> ) dominates charge current ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${I}_{c}$ </tex-math></inline-formula> ) in all the considered devices. A zero charge current was achieved by modulating temperature drop across the ASiNR-Ad based device, thus eliminating the Joule heating effect. Moreover, we observed an unprecedented giant thermal magnetoresistance (MR) of ~ <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${4.3}\times{10}^{{6}}\%$ </tex-math></inline-formula> in the ASiNR-Ad based device. These findings suggest that ASiNR-Ad can be employed effectively for energy harvesting and low-power applications utilizing spin current.