First-principles density functional theory study of strained wurtzite InP and InAs

International audienceWe report on semilocal and hybrid density functional theory study of strained wurtzite crystals of InAs and InP. The crystal-field splitting has a large and nonlinear dependence on strain for both crystals. Moreover, the study of the electronic deformation potentials reveals that the well-known quasi-cubic approximation fails to reproduce the electronic features of the non-ideal c/a ratio. This theoretical study is of crucial importance for the simulation of self-assembled InAs/InP nanowires

Vibrational properties of 2H-PbI2 semiconductors studied via Density Functional Theory calculations

International audienceDensity Functional Theory is used to study the vibrational properties of 2H-PbI2 semiconductor. The Born charge tensors are determined. Calculated phonon frequencies at the Brillouin zone center are compared to Raman scattering and IR absorption measurements. The computed Raman spectra show a good agreement with available experimental data. The simulated phonon dispersion curves are compared with triple-axis neutron scattering measurements

Optical properties of ultrathin InAs quantum-well-heterostructures

International audienceBand structure calculations of complete InAs monolayer in AlGaAs/GaAs quantum wells are performed within the framework of the extended-basis sp3d5s* tight-binding model. We show that the optical properties can be tuned from the quantum well energy below the GaAs band-gap depending on the well thickness and the position of the probe. The results are supported by differential reflectivity measurements and represent a concept for optoelectronic devices with an operation wavelength widely tuneable around 850 nm employing GaAs process technology

Etude de la stabilité des surfaces vicinales des métaux de transition à partir de leur structure électronique et vibrationnelle.

Study of the stability of vicinal surfaces in transition metals from their electronic and vibrational structures. This theoretical work is dedicated to the study of vicinal surfaces of Rh, Pd and Cu and, in particular, of their stability with respect to faceting. The manuscript includes three parts. It starts with the calculation of their surface energies, on a rigid lattice at 0K, using a tight-binding method with a basis set including s, p and d atomic valence orbitals. The energies of isolated steps are deduced from this calculation. They allow to determine the shape of adislands built by homoepitaxy on low-index surfaces, as well as step-step interactions which exhibit an oscillatory behavior. This behavior is strongly depending on the types of steps and surfaces. Kink energies are also computed by the same method. The electronic structure is briefly described. Then the vibrational properties of vicinal surfaces of Copper are studied using a semi-empirical potential which leads to good results for the relaxation of surfaces and describes correctly, in the harmonic approximation, their projected phonon band structure. It is thus possible to determine vibrational thermodynamical quantities, such as the root mean square displacement and the free energy. Finally, the stability of vicinal surfaces is discussed with semi-empirical potentials and with the calculation of electronic structure. It is shown that the stability can be inverted as a function of the potential range and that the atomic relaxation plays in favor of the stabilization of the surface but does not change qualitatively the results. Contrary to the semi-empirical potentials, electronic structure calculations open up the possibility of a large variety of behaviors, including a possible faceting of a vicinal surface into other vicinal surfaces. This phenomenon is due to electronic oscillatory step-step interactions. Finally, it is proven that the temperature has a minor effect on the stability of vicinal surfaces, at least up to room temperature.Etude de la stabilité des surfaces vicinales des métaux de transition à partir de leur structure électronique et vibrationnelle. Ce travail théorique concerne l' étude des surfaces vicinales de Rh, Pd et Cu et, en particulier, de leur stabilité par rapport à un facettage. L'étude comporte trois parties. Elle commence par le calcul de leurs énergies de surface, effectué sur réseau fixe à 0K, à l'aide de la méthode de liaisons fortes dans une base d'orbitales atomiques de valence s, p et d. Ces énergies permettent d'extraire les énergies de marches isol\ées, dont on déduit la forme des îlots en homoépitaxie sur les surfaces de bas indices, et lesi nteractions entre marches qui présentent un profil oscillant. Leur comportement est très différent selon les types de marches et de surfaces. Les énergies de cran sont déterminées par la même méthode. La structure électronique est brièvement décrite. Puis les propriétés vibrationnelles des surfaces vicinales de Cuivre sont étudiées en utilisant un potentiel semi-empirique qui donne de bons résultats pour la relaxation des surfaces et décrit correctement, dans l'approximation harmonique, leur structure de bande projetée de phonons. Il est ainsi possible de déterminer des quantités thermodynamiques vibrationnelles, telles que le déplacement carré moyen et l'énergie libre. Enfin, la stabilité des surfaces vicinales est discutée à l'aide de potentiels semi-empiriques et de calculs de structure électronique. Il est montré que la stabilité peut s'inverser en fonction de la portée du potentiel et que la relaxation atomique joue en faveur de la stabilisation des surfaces mais ne change pas qualitativement les résultats. Contrairement aux potentiels semi-empiriques, les calculs de structure électronique montrent une grande diversité de comportements incluant la possibilité de facettage des surfaces vicinales en d'autres surfaces vicinales. Ce phénomène est dû aux interactions électroniques oscillantes entre marches. Enfin, il est prouvé que, jusqu'à l'ambiante, la température a un effet mineur sur la stabilité des surfaces vicinales

Local wavefunction and exciton fine structure in extended-basis tight binding model

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