Представлено сравнительное исследование влияния вида локализующего потенциала на энергию связи биэкситона в сферически-симметричных квантовых точках A2B6. Предложенный критерий сравнения исследуемых потенциалов --- потенциального ящика, гармонического осциллятора и потенциала Гаусса --- базируется на одинаковой локализации в них носителей заряда одного знака. Расчеты энергии связи биэкситона выполнены вариационным методом в рамках kp-теории возмущений с учетом дополнительных поляризационных членов в волновых функциях электронной и дырочной подсистем, а также с учетом сложной структуры валентной зоны. Полученные результаты демонстрируют, что наличие плавно меняющегося потенциала конечной высоты в квантовых точках Cd(Zn)Se/ZnSe может приводить к более эффективной локализации в случае биэкситона по сравнению с экситоном, что представляет интерес для реализации быстродействующих излучателей квантового света. Работа выполнена при поддержке Российского научного фонда (проект N 14-22-00107). DOI: 10.21883/FTT.2017.06.44492.433
In the limit of strong quantum confinement the lower energy states of excitons and biexcitons in spheroidal quantum dots of semiconductors with a fourfold degenerate vertex of the valence band, which are active in the dipole approximation at one- and two-photon excitation, have been considered. The comparative analysis of the order of energy levels of the hole in the potentials of the infinitely deep quantum well and a three-dimensional harmonic oscillator taking into account the axial anisotropy of the quantum dot (QD) shape is carried out. It is shown that the anisotropy of the QD shape can lead to the opposite sign of splitting with respect to angular momentum projection ±3/2, ±1/2 for spatially odd (1 P _3/2) and even (1 S _3/2) levels of the hole. At the same time, in the case of the potential of an infinitely deep quantum well, an inversion of the order of 1 S _3/2 and 1 P _3/2 levels can be observed at values of the ratio of the effective masses of the light and heavy holes β = m _lh/ m _hh ≈ 0.14. The type of the trial wave functions of the hole for the state 1 P _3/2 in the potential of an isotropic three-dimensional harmonic oscillator depending on β is proposed. The dependence of the binding energy of excitons in the considered potentials on β is presented and the possibility of formation of various biexcitonic states is considered.
The electronic and hole states in quantum dots (QD) of cubic II–VI semiconductors with a spheroidal shape and uniaxial anisotropy have been studied theoretically. The smooth potential energy profiles simulated by the Gauss function in all three spatial directions are considered. The energy level lowering and the energy splitting of the hole state from the valence band top Γ_8 by momentum 3/2 into the states with projections ±3/2, ±1/2 on the anisotropy axis are analyzed. The QD anisotropies of three types are considered: the QD size anisotropy, the QD potential barrier anisotropy, and the combined anisotropy. In the first case, flattened quantum dots, in which the characteristic size in the structure plane is larger than the size along the anisotropy axis, are considered. In the second case, QDs, in which the potential barrier height in the plane is lower than that along the anisotropy axis, are considered. In the third case, flattened quantum dots with the anisotropy of the size and the potential barrier are considered. The conditions of the charge carrier localization inside QD have been found, and the influence of the form and composition anisotropies on the energies of exciton transitions in the structures with Cd_ x Zn_1 – _ x Se quantum dots are discussed.
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