| Graphene,silene,germaneneand phosphoenene,two-dimensional(2D)single-layer materials with one atomic thickness,have attracted interest in their research due to their unique properties.The superior properties of these materials stem from their single layer atomic thickness and network structure.Excellent performance has been extensively studied and used in many applications,such as high performance field transistors,optoelectronic devices,energy storage,sensors,and even biological applications.In general,most two-dimensional materials limit their use in electronic products due to the absence of band gaps.Germanane is a new generation of single-layer stable materials that have received wide attention in the field of two-dimensional materials.It is a graphane analogue,and its photoelectric properties have been extensively studied due to its direct band gap and high electron mobility.The effects of strain,doping and hydrogenation were investigated by first-principles calculations based on density functional theory.The first part studies the strain-induced changes in the monolayer structure of the germanane.The uniaxial strain destroys the hexagonal symmetry of the germanane,while the biaxial strain better preserves the symmetry of the structure.The band gap is non-linear in the zigzag strain,armchair strain and biaxial strain.Among them,the influence of biaxial strain on the band gap is the most obvious.In addition,the change in energy is asymmetrical under three strains,with biaxial strain making the most significant change in energy.The second part studies the energy band,electronic structure and optical properties of a single layer after germanium atoms are replaced by Ga and As atoms.Both dopings are thermodynamically stable.Due to the difference in the electronic structure of the two impurities,two different doping methods were employed.In order to make the structure more stable,when Ga is doped,the corresponding H atoms are removed,and As doping retains the corresponding H atoms.From the geometrical point of view,Ga has little effect on the lattice,while As doping makes the lattice structure relatively distorted.According to the band structure and local density analysis,gallium is p-type doped.The impurity band lowers the conduction band,causing the absorption spectrum to move in the infrared direction.The arsenic-doped impurity band passes through the Fermi level and is n-type doped.The calculation of optical properties confirms the analysis of band gap and doping properties.The third part studies the effect of hydrogenation on germanene.The electronic structure,phonon dispersion and thermal properties of germanene,germanane,SHgermanene and FHgermanene were investigated.Hydrogenation can effectively convert germanene from metallic materials to semiconductor materials.Among the three hydrogenated structures,germanane and FHgermanene are relatively stable structures,and SHgermanene is very unstable.This is mainly due to the fact that the Ge atoms in SHgermanene are unsaturated sp~2 orbital hybrids,while the Ge atoms in germanane and FHgermanene are more stable sp~3orbital hybrids.The structure of germanane is similar to germanene,and in the FHgermanene structure,all Ge atoms are almost in the same plane,and the folds are significantly reduced.After hydrogenation,all of the hydrogen atoms of the germanane remain on the same side,which results in a strong repulsion of the hydrogen atoms,an enhanced interaction of the H-s orbitals of the two hydrogen atoms,and a further expansion of the crystal.In order to further explore its performance,the phonon dispersion spectra of the four structures were analyzed..Since the phonon dispersion of germanane and FHgermanene have no negative values,the two structures here are stable.The germanane and FHgermanene structure has the same Ge/H ratio,so their thermal properties are consistent.The research in this paper has guiding significance for further mediating the need to change the properties of germanene to suit the application. |
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