Theory of Excitons Formed from Spatially Separated Electrons and Holes in Quasi - Zero - Dimensional Semiconductor Nanosystems (original) (raw)
Related papers
Quantum Dots - Theory and Applications, 2015
The theory of an exciton formed from a spatially separated electron and a hole is developed within the framework of the modified effective mass method. The effect of significantly increasing the exciton binding energy in quantum dots of zinc selenide, synthesized in a borosilicate glass matrix and relative to that in a zinc selenide single crystal is revealed. It is shown that the short-wavelength shift of the peak of the lowtemperature luminescence spectrum of samples containing zinc selenide quantum dots, observed under experimental conditions, is caused by quantum confinement of the ground-state energy of the exciton with a spatially separated electron and hole. A review devoted to the theory of excitonic quasimolecules (biexcitons) (made up of spatially separated electrons and holes) in a nanosystem that consists of ZnSe quantum dots synthesized in a borosilicate glass matrix is developed within the context of the modified effective mass approximation. It is shown that biexciton (exciton quasimolecule) formation has a threshold character and is possible in a nanosystem, where the spacing between quantum dots' surfaces is larger than a certain critical arrangement. An analogy of the spectroscopy of the electronic states of superatoms (or artificial atoms) and individual alkali metal atoms theoretically predicted a new artificial atom that was similar to the new alkali metal atom.
Excitons States in Semiconductor Quantum Dots
2016
It was found that within the band gap of the quantum dot of zinc selenide appears a zone of exciton states, located at the bottom of the conduction band. It has been shown that a decrease in the band gap width in this nanosystems conditioned by transition of the electron from quantum-dimensional level within the valence band of the quantum dot to the levels of the zone of exciton states. The dependence of the energy of a base state of an exciton from the radius of QD was obtained using a modified method of the effective mass.
Exciton Spectroscopy of Spatially Separated Electrons and Holes in the Dielectric Quantum Dots
Crystals
It is shown that in the potential energy of an exciton of spatially separated electrons and holes (hole moves in the amount of quantum dots (QDs), and the electron is localized on a spherical surface section (QD-dielectric matrix)) taking into account centrifugal energy gives rise band of the quasi-stationary surface exciton states that with the increase of the radius of QD becomes stationary state. The mechanisms of formation of the spectra of interband and intraband absorption (emission) of light in nanosystems containing aluminum oxide QDs, placed in the matrix of vacuum oil, are presented. It is shown that the electron transitions in the area of the surface exciton states cause significant absorption in the visible and near infrared wavelengths, and cause the experimentally observed significant blurring of the absorption edge.
Optical properties of exciton confinement in spherical ZnO quantum dots embedded in matrix
Superlattices and Microstructures, 2009
The optical characteristics of ZnO nanoparticles in SiO 2 matrix have been determined by UV-visible and photoluminescence (PL) studies. The PL spectrum of the ZnO quantum dots shows two different bands: the first one is a broad green emission band related to deep level emission in the visible range and the second one is situated at 3.48 eV in the ultraviolet region, and is attributed to the recombination of electrons in the conduction band and holes in the valence band. The experimental result that we found was simulated numerically using different methods. Our calculations revealed a good agreement between the matrix element calculation method and the experimental result. We have also calculated the ground state binding energy, the oscillator strength and the radiative lifetime of the exciton in a ZnO spherical quantum dot. It was clearly shown from our calculation that these physical parameters are very sensitive to the quantum dot size. As a consequence, the optical and electronic properties of the dot can be controlled and also tuned through the nanoparticle size variation. These results could be particularly helpful, since they are closely related to experiments performed on such nanoparticles; this may allow us to improve the stability and efficiency of semiconductor quantum dot luminescence, which is considered critical.
Exciton states in quasi-zero-dimensional semiconductor nanosystems
Semiconductors, 2012
For a semiconductor quantum dot (QD), the contributions made to the exciton energy spectrum by the electron and hole kinetic energies, the energy of Coulomb interaction between them, and the energy of their polarization interaction with the spherical interface between the QD and the dielectric medium have been analyzed.
Excitons in ZnO Quantum Dots: The Role of Dielectric Confinement
Journal of Physical Chemistry C, 2022
Quantum dots (QDs) grown by chemical synthesis methods are relatively unstable and present difficulties in dispersion and preservation. The most common way of surpassing the stability issues is to embed (and passivate) the QDs in a matrix material. However, some fundamental questions concerning the influence of the dielectric confinement caused by the matrix environment on the exciton energy and exciton binding energy of the QDs have not yet been properly addressed. Here we explore the exciton fine structure of wurtzite ZnO QDs by means of planewave million-atom atomistic pseudopotential calculations and a configuration interaction approach taking into account the dielectric confinement from the surrounding material. Our results indicate that the exciton energy increases and the exciton binding energy decreases as the dielectric constant of the surrounding material increases. The behavior of the exciton binding energy is caused by the presence of self-polarization potential induced by the dielectric mismatch in the surface of the QD. This mainly alters the localization of the hole charge density and thus reduces the electron−hole overlap and inevitably the exciton binding energy.
SURFACE
In review, deals with the theory of exciton quasimolecules (formed of spatially separated electrons and holes) in a nanosystems that consists of semiconductor and dielectric colloidal quantum dots (QDs) synthesized in a dielectric and semiconductor matrixs. It has been shown that the exciton quasimolecule formation is of the threshold character and possible in a nanosystem, where the distance D between the surfaces of QD is given by the condition (where and are some critical distance). We have shown that in such a nanoheterostructures acting as “exciton molecules” are the QDs with excitons localizing over their surfaces. The position of the quasimolecule state energy band depends both on the mean radius of the QDs, and the distance between their surfaces, which enables one to purposefully control it by varying these parameters of the nanostructure. It was found that the binding energy of singlet ground state of exciton quasimolecules, consisting of two semiconductor and dielectric Q...
Optical properties of acceptor–exciton complexes in ZnO/SiO2 quantum dots
Solid State Communications, 2011
The binding energy E b of the acceptor-exciton complex (A − , X) as a function of the radius (or of the impurity position of the acceptor) and the normalized oscillator strength of (A − , X) in spherical ZnO quantum dots (QDs) embedded in a SiO 2 matrix are calculated using the effective-mass approximation under the diagonalzation matrix technique, including a three-dimensional confinement of the carrier in the QD and assuming a finite depth. Numerical results show that the binding energy of the acceptor-exciton complexes is particularly robust when the impurity position of the acceptor is in the center of the ZnO QDs. It has been clearly shown from our calculations that these physical parameters are very sensitive to the quantum dot size and to the impurity position. These results could be particularly helpful, since they are closely related to experiments performed on such nanoparticles. This may allow us to improve the stability and efficiency of the semiconductor quantum dot luminescence which is considered critical.