Highly Thermoelectric Efficient Armchair Silicene Nanoribbons With Silicon Adatom Defects

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 ( ${N}={4}$ , 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 ( ${S}_{s}$ and ${S}_{c}$ ) values of 1200 and $1120 ~\mu \text{V}$ /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 ( ${Z}_{s}{T}$ and ${Z}_{c}{T}$ ) of ~64 and ~58, respectively, in the narrow device which is substantially higher than pristine ASiNRs having a ${Z}_{s}{T}={0}$ and ${Z}_{c}{T}={2.8}$ . Spin current ( ${I}_{s}$ ) dominates charge current ( ${I}_{c}$ ) 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 ~ ${4.3}\times{10}^{{6}}\%$ 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.