The influence of symmetry and structural factors on energy spectrum formation in the vicinity of band gap of complex semiconductors
Ivetta V. Slipukhina
Institute for Solid State Physics and Chemistry, Uzhgorod University, Ukraine
Mardi 11/09/2007, 10h00
Bât. C5 P.421B, CEA-Grenoble
Based upon the example of a narrow-band-gap semiconductor CdSb, it is shown that a spatial valence-electron density distribution in the unit cell is related to Zak's elementary energy bands creating the valence band and to the corresponding Wyckoff positions. General considerations are illustrated on the examples of valence energy bands in isovalent SnS and PbS crystals belonging to A4B6 group semiconductors with essentially different symmetry, as well as in their solid solution (Pb0.5 Sn0.5)S. It is suggested that the presented application of the elementary energy bands concept can be used as a simple method for obtaining charge localization centers in the crystalline lattice and thus for the construction of the well-localized Wannier functions. The effect of the shear strains on the topology of bands in the vicinity of band gap of strongly anisotropic SbSI and In4Se3 crystals is studied. The corresponding dispersion laws for electrons and holes are obtained. The changes in the band spectrum of copper- and lithium-intercalated In4Se3 crystals are investigated by means of first-principles calculations. The structural and electronic properties of SbSI crystals doped with Ni in one of the possible structural configurations was studied. First-principles structural relaxation in a supercell approximation revealed a five-fold distorted square-pyramidal coordination of the defect atom in the host material. The calculated spin-polarized electronic band spectrum shows that the substitution of Sb3+ by Ni2+ ion results in additional non-degenerate defect states localized within the forbidden gap. The Mulliken population analysis revealed the existence of a total magnetic moment of the cell of about 1 μB and showed that the configuration of substitutional Ni in SbSI is compatible with 3d7. The obtained non-integer values for the d-orbital population point at the strong p−d hybridization in the system. Laboratoire : L_Sim (en ukrainien).

 

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