Variable thermoelectric parameters in Si / Ge zNR by electrostrictive application of localized strain

Abstract

In this work, we propose the tuning of thermoelectric performance of zigzag monolayer Silicene and Germanene nanoribbon (SiNR/GeNR) with a reversible strain engineering method. By a proposed electrostrictive method a tensile or compressive moderate strain of ±2% orthogonal to the transport direction in a short region of the SiNR or GeNR is considered to be applied. A selfconsistent density functional tight binding (DFTB) approach is employed for the calculation of the electronic properties of the system, while the vibrational properties are computed with classical molecular dynamics simulations. Electron/phonon transport is computed with the Green’s function formalism. With the localized strain application it is observed that electron transmission and current through the Si or GeNR remains largely unaffected while a suppression of the phonon transport and thermal conductance can be achieved. A significant tuning is observed for thermoelectric figure of merit and variations are seen in the Seebeck coefficient and the thermoelectric power factor. Moreover the temperature and doping dependencies of these parameters also showed high degree of tunability with strain. The enhancements in thermoelectric figure of merit by such simple strain ON/OFF mechanism in a CMOS compatible architecture suggest good prospects for nanoscale thermoelectrics.