Tight-binding model for semiconductor nanostructures

Abstract

An empirical scp 3 a tight-binding (TB) model is applied to the investigation of electronic states in semiconductor quantum dots. A basis set of three p-orbitals at the anions and one s-orbital at the cations is chosen. Matrix elements up to the second nearest neighbors and the spin-orbit coupling are included in our TB-model. The parametrization is chosen so that the effective masses, the spinorbit-splitting and the gap energy of the bulk CdSe and ZnSe are reproduced. Within this reduced scp 3 a TB-basis the valence (p-) bands are excellently reproduced and the conduction (s-) band is well reproduced close to the Γ-point, i.e. near to the band gap. In terms of this model much larger systems can be described than within a (more realistic) sp 3 s * -basis. The quantum dot is modelled by using the (bulk) TB-parameters for the particular material at those sites occupied by atoms of this material. Within this TB-model we study pyramidal-shaped CdSe quantum dots embedded in a ZnSe matrix and free spherical CdSe quantum dots (nanocrystals). Strain-effects are included by using an appropriate model strain field. Within the TB-model, the strain-effects can be artifically switched off to investigate the infuence of strain on the bound electronic states and, in particular, their spatial orientation. The theoretical results for spherical nanocrystals are compared with data from tunneling spectroscopy and optical experiments. Furthermore the influence of the spin-orbit coupling is investigated.

Band gap bowing of binary alloys: Experimental results compared to theoretical tight-binding supercell calculations forCdxZn1−xSe

“…Furthermore, we incorporate an appropriate valence band offset (VBO) between the two materials by shifting the respective site-diagonal matrix elements by the value ∆E vb = 0.22 eV, as established in Ref. 20. Although this treatment of the intersite hopping and the VBO has merely been well-proven for interfaces in quantum dot systems, 18,19,22 our results for the bowing have turned out to be insensitive not only to the choice of the interface treatment but also to the specific value of ∆E vb (not shown).…”

Influence of symmetry and Coulomb correlation effects on the optical properties of nitride quantum dots

“…47 In the effective mass approximation or in the k · p theory the underlying atomic structure is not resolved, so that one obtains degenerate energies for the lens-shaped QD. 46,48,49 However, if one takes the crystal structure into account, as it is done, in a TB 33,50 or pseudo-potential calculation 51 , the symmetry will be reduced and degeneracies can be lifted. 46 For a lensshaped QD grown on a wurtzite lattice along the (0001)-direction, the symmetry is reduced to C 3v .…”

Optical properties of self-organized wurtzite InN∕GaN quantum dots: A combined atomistic tight-binding and full configuration interaction calculation

“…Being a technologically promising system, we study self-assembled InN/GaN QDs, which are typically grown by molecular beam epitaxy in StranskiKrastanov growth mode. A theoretical description of the one-particle states in terms of a tight-binding (TB) model is presented, which provides a powerful approach to the electronic states of low-dimensional heterostructures on an atomistic level 3,4 . For the calculation of optical absorption and emission spectra, full configurationinteraction (FCI) calculations 5,6 are used to obtain a consistent description of correlated many-particle states.…”