Tunable Electronic, Optical, and Thermal Properties of two- dimensional Germanene via an external electric field

Abstract

in this paper, we present a tight-binding model based on Dft calculations for investigation the electronic and optical properties of monolayer Germanene. the thermal properties are investigated using Green function method. the required tight binding parameters including the onsite energies and third nearest neighbors hopping and overlap integrals are obtained based on our Dft calculations. Germanene is a semiconductor with zero band gap and linear band dispersion around the K point. the band gap opening occurs in the presence of bias voltage. the band gap is increased linearly with increase of the bias voltage strength. The tight binding results for position of the two first peaks in the optical infrared region is same with the Dft results. By applying and increasing bias voltage, the dielectric function shows the blue shift by reduction the peak intensity in the energy range E < 1 eV. The thermal conductivity and heat capacity increase with increasing the temperature due to the increasing of thermal energy of charge carriers and excitation them to the conduction bands. the thermal properties of Germanene in the absence of bias U = 0 is larger than that U ≠ 0 and they decrease by further bias strength increasing, due to the increasing band gap with bias.Two-dimensional (2D) monolayer structures have been an active field of research due to their electronic, optical, and thermal properties. Graphene is a planar atomic layer of carbon atoms which they are arranged in a honeycomb lattice with 1.42 A° interatomic distance between two adjacent C atoms. Graphene has been an active field of research due to its important physical properties such as electronic structure with gapless properties, room temperature quantum Hall effects 1 and high intrinsic mobility 2 .In the graphene, the existence of a zero gap is due to the crossing between the valence and conduction bands at the K point (Dirac point). Near the K point, graphene exhibits linear energy dispersion in terms of momentum and its charge carriers behave as relativistic massless Dirac fermions described by a Dirac-like equation 3 . Note that, Materials with a zero band gap energy exhibit some fascinating and superior electronic properties compared to materials with a non-zero energy gap and they have intriguing physical properties and numerous potential practical applications in spintronics, electronics, optics and sensors 4 . The Dirac Spin-gapless semiconductors, have high carrier mobility and due to their real massless fermions and dissipation-less transport properties, they are regarded as promising candidates for applications in ultra-fast and ultra-low-power spintronic devices 5,6 .Several studies on electronic and optical properties of monolayer graphene have been reported via Density functional Theory (DFT) and Tight binding Theory (TB) 7-11 . Due to the zero band gap in graphene, the light absorption occurs in a wide range of spectra from infrared (IR) to ultraviolet which lead to the use of graphene in electro-optical devices. Using the first nearest neigh...

Effects of spin-orbit coupling and magnetic field on electronic properties of Germanene structure

“…The primitive unit cell vectors of honeycomb lattice have been shown by a 1 and a 2 . However Germanene is buckled due to sp2-sp3 combination of hybridization, the density functional theory calculations demonstrate the hopping amplitudes are dominant for electrons in orbital p z [37].…”

Tight–Binding Analysis of Electronic Structure of Germanene Sheet and Nanoribbons Including Stone-Wales Defect

“…In germanene (a monolayer of germanium atoms) the mixture of sp 2 and sp 3 hybridization causes a prominent buckling distance of 0.68Å [1,2]. Although bulk germanium is a significant indirect-bandgap semiconductor with excellent compatibility with silicon technology, but germanene, similar to graphene, shows linear dispersion relation around the K and K' points of the first Brillouin zone, in which the conduction band (CB) and the valence band (VB) touch each other [3,4]. Owing to the spin-orbit interaction in germanene, it has massive Dirac fermion, unlike to massless fermions in graphene [4,5].…”

“…Although bulk germanium is a significant indirect-bandgap semiconductor with excellent compatibility with silicon technology, but germanene, similar to graphene, shows linear dispersion relation around the K and K' points of the first Brillouin zone, in which the conduction band (CB) and the valence band (VB) touch each other [3,4]. Owing to the spin-orbit interaction in germanene, it has massive Dirac fermion, unlike to massless fermions in graphene [4,5]. The effective electronic masses (m * ) of graphene and germanene are 0 and 0.007m0, respectively.…”

“…The effective electronic masses (m * ) of graphene and germanene are 0 and 0.007m0, respectively. Atom-atom bond length of germanene is 2.431Å, whereas it is 1.422Å for graphene, and lattice constant of germanene and graphene are 4.043Å and 2.463Å, respectively [2][3][4][5]. Since Ge-Ge bonds of germanene are more flexible than C-C ones of graphene, the elastic constant of germanene with the highest buckled structure and graphene with no buckled structure are 56.01(Jm -2 ) and 328.02(Jm -2 ), respectively [6].…”

“…Study of the phonon spectrum has demonstrated that the lattice of germanene is stable against up to 16% strain and the Dirac cone shifts towards higher energies when the strain is increased [4].…”