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International audience; We have calculated the exciton fine structure splittings (FSS) of asymmetric GaAs/AlGaAs quantum dots (QDs) obtained after Al droplet epitaxy and subsequent nanoholes formation followed by annealing and GaAs filling of nanoholes. We used a k • p model and considered the heavy-hole and light-hole mixing to calculate the electron-hole exchange interaction (EI). The two components, long-range (LR) and short-range (SR) of the EI, were deduced. The exciton fine structure is organized, as usual in zinc-blende compounds, into two groups of states: bright (optically active) and dark states. The bright-dark and bright-bright splittings contain LR and SR contributions, the LR part representing 5 to 68% of the total bright-dark splitting and 69 to 76% of the total bright-bright splitting for sizes experimentally explored. In QDs having C 2v symmetry, LR and SR contributions to dark-dark splitting have to be calculated at the second order of perturbation theory. A good agreement between the theory and experiment is obtained for QDs with different degrees of asymmetry, from QD having an isotropic shape to QD with a very anisotropic shape.

We investigate the theoretical band structure of organic–inorganic perovskites APbX3 with tetragonal crystal structure. Using D4h point group symmetry properties, we derive a general 16-band Hamilt...

We investigate the theoretical band structure of organic-inorganic perovskites APbX

International audience; Since their first synthesis in 2015, the all-inorganic lead halide perovskite nanocrystals CsPbX3(X=Cl,Br,I) have attracted a great deal of attention due to their outstanding electronic and optical properties as well as their performances, which outclass the ones of their II–VI conterparts in many application fields. In addition to these properties, the understanding of the emission features in these systems at the single object scale is crucial, e.g., for nanophotonics and quantum optics devices. Here, the details of the band-edge excitonic emission are theoretically explored. The contribution of the long-range exchange interaction to the bright-exciton splittings is computed in strong and weak confinement regimes using group theory arguments and k⋅p approximation. We show that the shape anisotropy with the real crystalline (cubic, tetragonal, or orthorhombic) structures of nanocrystals explain well their emission properties. In the weak confinement regime, splittings are inversely proportional to the cube of the exciton Bohr radius and we observe an increase of the splittings from iodide, to bromide, and then to chloride perovskite compounds. However, in the strong confinement regime, splittings increase inversely proportional to the nanocrystal volume and, for a given nanocrystal size, the splitting values are comparable for the three-halide-perovskite materials. The present theoretical developments lead to quantitative contributions in good agreement with available experimental data mainly in the weak confinement regime.

The effects of the Aluminium concentration on the emission of Al 0.45 In 0.55 As/Al y Ga 1− y As quantum dots (QDs) are investigated by photoluminescence (PL), with the excitation power density as a variable parameter. The influence of a varying barrier composition on the QD emission is investigated theoretically and discussed with respect to PL measurements. For the highest barrier composition value ( y = 0.77), we interpret the QD emission as originating from indirect type-II transitions involving electrons in the barrier X valley and heavy holes (HH), with S and P symmetry, in Al 0.45 In 0.55 As QDs. The PL spectra of the y = 0.38 sample exhibits three lines: two of them are related to indirect type-II transitions, in which the electron ground state belongs to the indirect gap (L and X) minima in the barrier conduction band, whereas the third transition is attributed to a direct type-I transitions.

We present an experimental and theoretical study of the optical properties of asymmetric strain-free GaAs quantum dots (QDs) fabricated by filling of self-organized nanoholes (NHs) created by local droplet etching. The energy levels are calculated within the effective mass approximation using as input a model anisotropic QD shape with C 2 v symmetry based on atomic force microscopy (AFM) profiles of NHs. The influence of the QD height and shape anisotropy on the exciton emission energy and the s- p x and s- p y energy splittings is studied theoretically. The experimentally observed bound nature of excitonic states is well reproduced by our theoretical approach which includes direct Coulomb energies and correlation effects. We investigate the fine-structure splitting (FSS) of the neutral exciton as a function of dot size. Theoretical calculations of the long-range electron-hole (e-h) exchange interaction predict an increase of the FSS with decreasing QD height, which describes well the experimental trend.

We report photoluminescence (PL) characterization and model simulation of AlInAs/AlGaAs type-II quantum dots (QDs). A thorough and precise determination of the band parameters for QD and matrix materials is given, focusing on the effects of alloy composition and strain state on the electronic properties. Origins of experimentally observed PL emission peaks are identified through a comparison with the band lineup theoretically determined in this work. We interpret the QD emission as originating from indirect type-II transitions involving electrons in the barrier X valley and heavy holes with S and P symmetry.

Using third and fourth order perturbation theory inside a 14-band and 30-band k ⋅ p model, we have calculated the effective Lande factor g ∗ of Γ 6 C conduction electrons in GaAs and AlSb. A strong variation between both models is observed. We show that the 14-band formalism even in fourth order perturbation theory is not sufficient to predict an experimental data of g ∗ . However, results deduced by the 30-band k ⋅ p model are consistent with experimental data. In particular, the k ⋅ p Hamiltonian parameters are adjusted such that the g ∗ of GaAs and AlSb are respectively −0.391 and 0.81, in excellent agreement with the experimental values of −0.44 and 0.84.

We present a generalized theoretical description of the 30 × 30 k ⋅ p approach for determining the band structure of the direct-band-gap semiconductors (InAs, InP, InSb), including the d far-levels contribution. For all materials investigated, the resulting electronic band structure parameters are in good agreement with experimental values. This model gives access to the second conduction band which is useful for transport modelling. We finally show that this method also gives explicit expressions for the Luttinger parameters, the κ valence band parameter and the effective masses in the Γ valley.

A quantitative comparison of different k · p calculations of valence-band states in quantum-confined semiconductor heterostructures is presented. The importance of using the appropriate Hamiltonian form is studied quantitatively following a numerical method which enables discrimination between existing Hamiltonians. The correct form of the Hamiltonian appears to be the Foreman Hamiltonian, which gives physically reasonable results contrary to the symmetrized Hamiltonian.

The band structure of direct-band-gap semiconductor (InAs) and indirect-band-gap semiconductor (Ge) is described theoretically using a 20×20 k.p model and including far-level contribution (essentially the d levels). By using this model, we obtained a quantitatively correct description of the top of the valence band and the lowest two conduction bands both in terms of energetic positions and band curvatures. In particular, the k.p Hamiltonian parameters are adjusted such that the transverse mass of the germanium conduction band is equal to the experimental value of 0.081.

We study the effects of the pc–pc coupling in intersubband hole optical transitions in SiGe/Si quantum wells for x and z polarizations. We have used a k⋅p model taking into account both the p-like first conduction band and the s-like second conduction band. First, we have found a unitary transformation that block diagonalizes the 14×14 Hamiltonian (or 12×12 Hamiltonian) into two 7×7 (or 6×6) blocks that are real symmetric in the finite difference formulation. We find that pc–pc interaction plays a minimal role in intersubband optical transition for x and z polarizations. Moreover, our calculations clearly confirm that the pc–pv coupling favors intersubband transitions for an optical polarization parallel to the layer plane (x polarization). In addition, for z polarization, both s–pv and pc–pv interactions play an equal footing role in intervalence band transitions.

International audience; The effect of the lattice-mismatch strain and of the charge carrier confinement profile, on the optical properties of thermally annealed self-assembled InxGa1-xAs/GaAs quantum dots (QDs), is theoretically analyzed by using a recently developed 40-band k.p model. First, to evaluate the composition and size of QDs as a function of thermal annealing conditions, we model the In/Ga interdiffusion by a Fickian diffusion. Second, we investigate the decrease of the strain effects on the carrier confinement potentials with annealing by solving the Schrodinger equation separately for electrons and holes. It is clearly found that the strain strongly modifies the QD potential profile, leading to a different electron and hole energy distribution. Finally, we carry on a comparison between theoretical calculations and photoluminescence (PL) experimental results performed in thermal annealed samples. A good agreement is obtained for the energy blueshift and the linewidth narrowing of the PL spectra measured on annealed QD ensemble. These results prove the relevance of the present approach to describe the optoelectronic properties of the nanostructures through the post-growth thermal annealing treatment.

A 40-band k⋅p model is used to compute the standard k⋅p band parameters at Γ, X, and L valleys in direct-band-gap bulk materials for Td group semiconductors. The values of the effective masses for electrons, heavy holes, and light holes in the Γ, X, and L valleys are in good agreement with those reported in other publications. Satisfactory agreement with available experimental data is also obtained by the present model. Finally, our results show that the effective Lande factor g∗, the κ valence band parameter, and the Dresselhauss spin-orbit coupling constant δ conicide well with available experimental data. The k⋅p Hamiltonian parameters, in particular, are adjusted to get g∗(GaAs)=−0.42, which turn out to be in agreement with the experimental value of −0.44.

The band structure of direct-band gap semiconductors (GaAs, InAs, InP) is described theoretically by using a 34×34 k⋅p model. We extend the sp3d5 basis functions by the inclusion of sV∗ orbitals. We find that the sp3d5s∗ k⋅p model is sufficient to describe the electronic structure of all materials investigated over a wide energy range, obviating the use of any d valence orbitals. Finally, our results show that Luttinger parameters, the κ valence band parameter, the effective Lande factor g∗, and the effective-masses in the X and L valleys are in good agreement with available experimental data. In particular, the adjustment of the k⋅p Hamiltonian parameters proved that g∗ of GaAs, InAs, and InP are, respectively, −0.41, −15.82, and 1.35, which are in good agreement with the experimental values of −0.44, −14.90, and 1.26.

A 34-band k ⋅ p model is used to compute the standard k ⋅ p band parameters at Γ, X and L valleys in indirect-band-gap bulk materials for Td (AlAs) and Oh (Si, Ge) group semiconductors. The values of the effective masses for electrons, heavy and light holes in the Γ, X and L valleys are in very good agreement with those reported in other publications. Satisfactory agreement with available experimental data is also obtained by the present model. Finally, our results show that the Luttinger parameters, the κ valence band parameter and the effective Lande factor g* are in good agreement with available experimental data. In particular, the adjustment of the k ⋅ p Hamiltonian parameters proved that the g* of AlAs, Ge and Si are respectively 1.50, −2.79 and 1.96, which are in good agreement with the experimental values of 1.52, −2.50 and 1.99.

The band structure of indirect-band gap semiconductors (AlAs, GaP) as well as indirect-band gap alloys semiconductors (GeSi) is described theoretically by using a 30×30 k×p model including the d far-level contribution. For all materials investigated, the resulting electronic band structure parameters are in good agreement with experimental values. The method also provides a good description of the second conduction band which is useful for transport modeling. Finally, our results show that Luttinger parameters, the κ valence band parameter, and the effective masses in the X and L valleys are in good agreement with available experimental data.