Modulation of electronic bandgaps and subsequent implications on SQ efficiencies via strain engineering in ultrathin SnX (X = S, Se) nanowires

Abstract

First-principles calculations have been undertaken to theoretically model ultrathin SnX (X = S, Se) nanowires (NWs). The formation energies of the ultrathin SnX NWs are negative and lower than those of their two-dimensional (2D) counterparts, suggesting the ultrathin NWs to be more viable for experimental syntheses. The absence of imaginary frequencies in the phonon dispersion curves for the ultrathin SnX NWs indicates the dynamic stability of the modelled structures at 0 K. The ultrathin SnS and SnSe NWs show indirect bandgaps of 2.038 eV and 1.931 eV, respectively. The corresponding SQ efficiencies are 22.44% and 24.75%. Furthermore, strain engineering has been undertaken to modulate the electronic bandgaps to subsequently amplify the SQ efficiencies of the ultrathin SnX NWs. The applied strain is in the range of −10% compressive to +10% tensile along the Z-direction. The formation energies still remain negative for the strained ultrathin SnX NWs. However, an indirect to direct band transition occurs at −2% and −4% compressive strains for the ultrathin SnS and SnSe NWs, respectively. The bandgap remains indirect upon the application of tensile strains in the ultrathin SnX NWs. It is observed that the SQ efficiencies get amplified with strain engineering. In the case of ultrathin SnS NWs, the SQ efficiencies reach 29.28% and 31.71%, respectively, at −10% and +10% strains. For the ultrathin SnSe NWs, the SQ efficiencies reach 33.76% and 33.70% at −10% and +10% strains, respectively. The electron and hole mobilities of the ultrathin SnX NWs are much higher than those of their 2D counterparts, which means that the ultrathin SnX NWs are more suitable for the fabrication of next generation nano-electronic devices. In particular, ultrathin SnS NWs show an ultrahigh electron mobility of 98.435 × 10⁴ cm² V⁻¹ s⁻¹.