Hydrogen sensitive field-effect transistor based on germanene nanoribbon and optical properties of hydrogenated germanene

Physisorption of hydrogen molecules on armchair germanene nanoribbon (GeNR) is studied with density functional methods. The adsorption geometries, adsorption energies and transferred charge are obtained. To take the Van der Waals forces into account, the Grimme correction is added to the calculation method. The physisorption effect on the electrical properties of the ribbon is explored as a function of concentration through the Green's function techniques. Sensing features of the GeNR are investigated as a channel of a back gated field effect transistor. The optical properties of the nanoribbon are obtained for parallel and perpendicular polarizations. The results point out that, the germanene is a suitable substrate for encapsulation. Moreover, physisorption can improve the I-V characteristics and suppress the optical spectrum of the GeNR. The current through the nanoribbon increases by increasing concentration at the same bias voltage. Also, the germanene back gated FET improve the sensing properties. The results show that the GeNR dielectric function is anisotropic and the GeNR becomes more transparent by increasing density. Finally, by applying the spin-orbit coupling (SOC) effect, the obtained results are re-calculated and the changes in the results are studied. The SOC opens up the electronic band gap of the GeNR about 20 meV and increases the current slightly through the GeNR.