Formation of Dirac point and the topological surface states inside the strained gap for mixed 3D Hg1−xCdxTeHg1−xCdxTe

•Effect of tensile strain on mixed 3D HgCdTe TI layers is studied.•The Cd dopant changes the localization Dirac Point and shape of the Dirac cones.•Different lattice mismatch together with x  -Cd<0.155<0.155 increases the gap induced by strain.

In this paper the results of the numerical calculation obtained for the three-dimensional (3D) strained Hg1−xCdxTeHg1−xCdxTe layers for the x-Cd composition from 0.1 to 0.155 and a different mismatch of the lattice constant are presented. For the investigated region of the Cd composition (x   value) the negative energy gap (Eg=Γ8−Γ6Eg=Γ8−Γ6) in the Hg1−xCdxTeHg1−xCdxTe is smaller than in the case of pure HgTe which, as it turns out, has a significant influence on the topological surface states (TSS) and the position of the Dirac point. The numerical calculation based on the finite difference method applied for the 8×8 kp model with the in-plane tensile strain for (001) growth oriented structure shows that the Dirac cone inside the induced insulating band gap for non zero of the Cd composition and a bigger strain caused by the bigger lattice mismatch (than for the 3D HgTe TI) can be obtained. It was also shown how different x-Cd compounds move the Dirac cone from the valence band into the band gap. The presented results show that 75 nm wide 3D Hg1−xCdxTeHg1−xCdxTe structures with x≈x≈0.155 and 1.6% lattice mismatch make the system a true topological insulator with the dispersion of the topological surface states similar to those ones obtained for the strained CdTe/HgTe QW.