The influence of an external uniform in-plane electrostatic field on the exciton states in a CdSe nanoplatelet (NPL) is considered theoretically. By considering the jump in permittivity at the NPL-medium boundary, the energy spectrum and spatial distribution of the probability density for free carriers and 2D excitons in the presence of an in-plane electric field are obtained. The Stark shifts for a 2D exciton are calculated, and it is shown that for fields above a certain critical value, the exciton decays into an electron and hole pair. It is shown that the field critical value increases with a decrease in the number of monolayers in the direction of strong NPL quantization. The exciton decay rate dependence on the in-plane electric field has been calculated. The main decay mechanisms have been identified for regions of weak and strong electric fields. For the field values less than the critical exciton radiative decay time, calculations of ionization time via tunneling of an exciton are presented. Along with the dependence on the external field, their dependence on the number of monolayers in the direction of strong quantization and the depth of the quantum well NPL in the lateral direction is also shown. For a strong electric field, single-particle states are studied in the NPL plane, and an estimate is given for the tunneling time of electrons through the barrier created by the field for charge carriers in the lateral direction after exciton decay.

The thermodynamic and magnetic properties of weakly interacting electron gas localized in a CdSe cylindrical core–shell quantum dot in the presence of axial magnetic field are investigated. The entropy, mean energy, and heat capacity of such a gas are determined, and its magnetic properties (magnetization and diamagnetic susceptibility) are studied. The possibilities of controlling thermodynamic parameters by changing the geometric parameters of quantum dots are shown. Calculations show that this gas has diamagnetic properties. These results provide insights into the features of physical processes occurring in thin core–shell quantum systems, which have potential applications in opto- and nanoelectronics.

Vacuum Fourier spectrometer was used to obtain mid-infrared photoinduced absorption spectra of undoped GeSi/Si quantum dots at liquid helium temperature under different conditions of interband optical pumping. High-intensity peaks in the absorption spectra are associated with intraband hole transitions from the ground and excited states of the quantum dot to the continuous spectrum. The less intense long-wavelength peak corresponds to the hole transitions between the ground and excited states. In the terahertz spectral range, equilibrium absorption spectra were obtained, associated with transitions from the ground to a nearby excited state of holes. Structures with GeSi/Si quantum dots can be used to develop detectors of mid-infrared radiation.

In the effective mass approximation, single-particle, excitonic states, and interband and intraband transitions in CdSe nanoplatelet are considered in the presence of an external axial uniform electrostatic field. It has been demonstrated that under the influence of the field, the binding energy between the electron and the hole in the nanoplatelet decreases compared to the case in the absence of the field. It is shown that with increasing electric field strength, the resonant frequencies of interband electroabsorption undergo a red shift. On the other hand, the resonance frequencies of intraband absorption shift to the region of high energies. A similar shift of photoluminescence spectrum peaks under the influence of the field has been observed. The results of theoretical calculations of the luminescence threshold frequency values are in good agreement with the corresponding experimental data. It is shown that the dependence of the optical rectification peaks on the external field is non-monotonic with pronounced maxima.

The results of comprehensive studies of near-infrared photoluminescence and mid-infrared equilibrium and photoinduced absorption spectra in structures with Ge/Si quantum dots with different doping levels at different optical pumping intensities and different temperatures are presented. Obtained dependences of interband photoluminescence spectra on temperature and optical pumping intensity are explained by the change in the intensities of direct and indirect in real space electron-hole recombination in Ge/Si quantum dots. The spectra of equilibrium and photoinduced absorption of polarized mid-infrared radiation demonstrate peaks associated with transitions of holes from the ground and excited states to continuum states above quantum dots and with optical transitions from the ground states to excited ones.

Abstract The theoretical investigation of interband and intraband transitions in asymmetric ellipsoidal InAs quantum dot have been considered. The interband absorption coefficient dependencies from quantum dot geometrical parameters have been calculated. Linear and nonlinear absorption spectra behaviors have been observed for different geometrical sizes. Also, the second and third harmonic generation coefficients have been studied.

The thermodynamic characteristics of an electron gas localized in a thin spherical CdSe nanolayer have been studied. The dimensions of the CdTe/CdSe core-shell type quantum dot are considered large, which allows the gas to be considered ideal. Due to the small thickness, the particle spectrum has a subband character, when a family of levels of the spherical rotator is associated with each radial quantization level. Within the framework of Boltzmann statistics, the statistical sum for the gas under study was determined, as well as the mean energy, entropy, and heat capacity. The dependences of the thermodynamic characteristics of the electron gas on the geometric parameters of a CdTe/CdSe quantum dot have been studied.

Nanostructures with quantum dots based on GeSi solid solution are promising for the development of optoelectronic devices compatible with modern silicon technology. In this paper, we demonstrate the capabilities of such nanostructures for detecting infrared and terahertz radiation. The working spectral range of nanostructures with GeSi/Si QDs is determined by the energy position of hole levels in the QDs, which is calculated using the quantum box model and confirmed by experimentally measuring the spectra of photoinduced intraband absorption of radiation. Using time-resolved spectroscopy, we found the characteristic times that determine the speed of the detection process associated with the processes of capture and recombination of charge carriers.

This paper theoretically studies the impurity states and the effects of impurity concentration and configuration on the optical, electrical, and statistical properties of CdSe nanoplatelets (NPLs). An image charge-based model of electron-impurity interaction is proposed. The charge-carrier energy spectra and corresponding wave functions depending on the impurity number and configuration are calculated. The electron binding energies are calculated for different NPL thicknesses. It is shown that the image charge-based interaction potential that arises due to the dielectric constants mismatch is much stronger than the interaction potential that does not take such a mismatch into account. Also, it is demonstrated that the binding energies are increasing with the number of impurities. We calculate the canonical partition function using the energy levels of the electron, which in turn is used to obtain the mean energy, heat capacity, and entropy of the non-interacting electron gas. The thermodynamic properties of the non-interacting electron gas that depend on the geometric parameters of the NPL, impurity number, configuration, and temperature are studied.

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Influence of dielectric confinement in exciton–biexciton energetic ordering.

The thermodynamic characteristics of a pair-interacting hole gas localized in a Ge/Si lens-shaped quantum dot are studied. The pair-interaction potential is modeled by the oscillator function, which depends on the distance between the particles. The analytical form of the spectra makes it possible to calculate the partition function in Boltzmann approximation. Based on the partition function mean and free energies, heat capacity and entropy of the interacting gas are calculated. Interaction between particles substantially changes the behavior of the thermodynamic properties in comparison with the non-interacting gas case. In particular, the gas undergoes a first-order phase transition driven by the height of the upper (or lower) section of QD, resulting in a changing symmetry of the lens-shaped QD.

Intraband linear and nonlinear optical absorption in a strongly oblate lens-shaped Ge/Si quantum dot in the presence of an axial magnetic field was theoretically studied. Quantum transitions are considered in the heavy hole subband, when the scalar effective mass approximation is correct. The linear and nonlinear absorption coefficients, refractive index changes and the second harmonic generation coefficient were determined. The influence of the effects of temperature, size quantization and magnetic field on the behavior of the above parameters was revealed.

In the presence of the axial magnetic field, the behavior of the electron in the colloidal CdSe nanoplatelet containing multi-impurity centers has been investigated. The two-dimensional Schrodinger equation with the effective potential of the interaction of electron and impurity centers, localized in the central plane of the nanoplatelet has been obtained. It has been shown that the magnetic field influence on the electron energy levels weakens with increasing the number of impurities.

An analytical model of a pair-interacting electron gas localized in an asymmetric biconvex strongly oblate lens-shaped GaAs quantum dot has been considered. The wave functions and the energy spectrum of the system have been calculated in the frame of the exactly solvable two-dimensional Moshinsky model. The character of long-wavelength transitions between the center of mass levels of the system have been obtained when the generalized Kohn’s theorem is realized.

Abstract The nonlinear optical properties (second and third harmonic generations) in CdSe nanoplatelets were theoretically studied. The energy spectra and wave functions of the hole in the considered system were calculated with the finite element numerical method. Quantum transitions are considered in the hole subband. The second and third harmonic generation coefficients were determined. The influence of the number of nanoplatelet monolayers on the character of the second and third harmonic generation coefficients has been studied.

The quasi-two-dimensional exciton subsystem in CdSe nanoplatelets is considered. It is theoretically shown that Bose–Einstein condensation (BEC) of excitons is possible at a nonzero temperature in the approximation of an ideal Bose gas and in the presence of an “energy gap” between the ground and the first excited states of the two-dimensional exciton center of inertia of the translational motion. The condensation temperature (Tc) increases with the width of the “gap” between the ground and the first excited levels of size quantization. It is shown that when the screening effect of free electrons and holes on bound excitons is considered, the BEC temperature of the exciton subsystem increases as compared to the case where this effect is absent. The energy spectrum of the exciton condensate in a CdSe nanoplate is calculated within the framework of the weakly nonideal Bose gas approximation, considering the specifics of two-dimensional Born scattering.

This paper theoretically studies the impurity states and the effect of impurity concentration and configuration on the optical, electrical, and statistical properties of CdSe nanoplatelets (NPLs). The image charge-based model of electron–impurity interaction has been proposed. The charge carrier energy spectra and corresponding wave functions depending on impurity number and configuration have been calculated. The electron binding energies have been calculated for different NPL thicknesses. It has been shown that the image charges-based interaction potential that arises due to the dielectric constants mismatch is much stronger than the interaction potential that does not take such a mismatch into account. Also, it has been demonstrated that binding energies are increasing with the number of impurities. We calculated the canonical partition function using the energy levels of the electron, which in its turn is used to obtain the mean energy, heat capacity, and entropy of the noninteracting electron gas. The thermodynamic properties of the noninteracting electron gas depending on the geometric parameters of the NPL, impurity number, configuration and temperature have been studied.

The current work used the effective mass approximation conjoined with the finite element method to study the exciton states in a conical GaAs quantum dot. In particular, the dependence of the exciton energy on the geometrical parameters of a conical quantum dot has been studied. Once the one-particle eigenvalue equations have been solved, both for electrons and holes, the available information on energies and wave functions is used as input to calculate exciton energy and the effective band gap of the system. The lifetime of an exciton in a conical quantum dot has been estimated and shown to be in the range of nanoseconds. In addition, exciton-related Raman scattering, interband light absorption and photoluminescence in conical GaAs quantum dots have been calculated. It has been shown that with a decrease in the size of the quantum dot, the absorption peak has a blue shift, which is more pronounced for quantum dots of smaller sizes. Furthermore, the interband optical absorption and photoluminescence spectra have been revealed for different sizes of GaAs quantum dot.

The theoretical investigation of one- and few-particle states in asymmetric biconvex lens-shaped Ge/Si quantum dot have been considered. Heavy hole transitions in considered structure have been studied. The behaviors of linear and nonlinear absorption coefficients for different quantum dot geometric parameters have been observed. Pair-interacting few-heavy hole gas has been investigated by modeling the interaction potential between holes in the frame of Moshinsky model. The character of long-wave transitions between the center of mass levels of the system have been obtained when Kohn theorem is realized.