First-principles Calculations Of Electronic Structure And Elastic Properties Of Sn And Its Alloys

Group IV materials represented by silicon have excellent properties in many aspects.It has high thermal conductivity and is also an excellent optical waveguide material.However,the use of Group ? semiconductors to make light-emitting devices has an inherent disadvantage:indirect band gap materials.For example,the probability of radiant luminescence after silicon carrier transition recombination is very low.The luminous efficiency of silicon in the room is roughly in the order of 10-7?10-6,which is tens of thousands of times smaller than ordinary semiconductor light-emitting materials?direct bandgap semiconductor materials?.It is difficult to prepare a light source with high luminous efficiency.It is found that Sn,which belongs to the same family as Si and Ge,has a direct band gap.If tin can be pasted on Si,Ge and other materials,the reasonably reduced first-principles calculation method based on density functional theory in this paper will be necessary.The lattice constants,band structures and elastic constants of GeSn,SiSn and GeSiSn alloys are systematically studied.The calculation results are as follows:For GeSn alloys,the composition-dependent properties of the lattice constant show a weak positive deviation from Vegard's law.The bending factor is bA=-0.083 A.For the band structure,it can be found that when the Sn content is about 0.31,the band gap of Ge1-xSnx becomes 0 eV.The bending coefficients of Eg?-? show obvious component-dependent characteristics,while the bending coefficients of Eg?-x and Eg?-L have weak dependence on the components.Because the atom size mismatch between Ge and Sn atoms is large,and the electronegativity difference between them is relatively small,when determining the component-dependent characteristics of by,the atom size mismatch plays more than the electronegativity difference important role.The decrease in Eg?-? bending coefficient is due to the fact that as the Sn composition increases in the Ge-rich range,the direct band gap will gradually transition from the impurity-like region to the energy-like region.According to the fitting results,when approximately 6%of the Ge atoms are replaced by Sn atoms,a transition from an indirect band gap to a direct band gap occurs.The band gap curvature of Ge1-xSnx is larger than that of Si1-xGex.It is not a difference in electronegativity and should be attributed to the atomic size mismatch.In addition,the bending coefficient of the valence band top?VBM?is smaller than the bending coefficient of the conduction band bottom?CBM?.Since VBM only shows p-track features.The CBM shows p-orbital and s-orbital characteristicsFor the SiSn alloy,the data of pure Si were first calculated,and it was found that both the lattice parameter,the band gap value,and the band gap widths of the X,L,and? energy valleys were in good agreement lattice constant.It is found that the lattice constants of SiSn alloys show similar properties to GeSn alloys.With the increase of Sn composition,the lattice parameters of SiSn alloys gradually increase,The study of the density of states found that the valence band top is mainly composed of Si3p and Sn 5p The p-p coupling between them works;the analysis of the milluken electronic layout shows that only Si₁Sn₇ alloys have pure metal bonds in the entire Si_1-xGe_x composition,indicating that the SiSn alloy bonds and bonds have a strong interaction at this time.For GeSiSn alloys,the parameters of lattice constant,unit cell volume,and bulk modulus of Ge₁₅Si₄Sn₁,Ge₁₀Si₈Sn₂ and Ge₅Si₁₂Sn₃ are mainly studied.The calculation results show that in terms of the band structure,the band structure and the density map of states are analyzed in detail.The content of Si and Sn in the alloy increases at a ratio of 4:1,and the forbidden band width gradually increases.The bottom of the valence band moves slowly with the incorporation of Si and Sn components,which provides a theoretical reference for further refinement of direct band gap GeSiSn materials.