Strain dependent electronic transport of pristine Si and Ge nanowires

Abstract

We have studied strain governed electronic structure and transport properties of Si nanowire (SiNW) and Ge nanowire (GeNW) utilizing generalized gradient approximation (GGA) of density functional theory (DFT). The SiNW and GeNW have a direct bandgap of 1.699 eV and 1.491 eV, respectively, at Γ point. The bandgap of SiNW for the intrinsic and uniaxial strain of −6% to 2%, and bandgap of GeNW for a compressive strain of 2% and 4%, is more than 1.5 eV; therefore, these Si/GeNW has potential applications in optoelectronic devices. The work function of Si/GeNW reduced drastically on applying compressing strain. For all the value of compressive strain, electrical and electronic thermal conductivity is higher than the relaxed SiNW; contradictory for tensile strain electrical, and electronic thermal conductivity is less than the relaxed SiNW. While for the all strained GeNW, the electrical and electronic thermal conductivity reduces drastically compared to strain-free GeNW. All strained GeNW have very low electronic thermal conductivity and a very high Seebeck coefficient as compared to strain-free GeNW. The figure of merit is high for SiNW, and it is greater than 1 in the range of 300 K to 600 K for an intrinsic tensile strain of 4%. GeNW for an intrinsic and uniaxial compressive strain of 8%, the value of ZTe is near one at 300 K and remains almost constant up to 800 K. High figure of merit of SiNW, very high Seebeck coefficient of GeNW and very low thermal conductivity of GeNW encourage using Si/GeNW as thermoelectric devices but is not limited to the thermoelectric generator or heat pump.