D. B. Hayrapetyan

Electron States and Light Absorption in Strongly Oblate and Strongly Prolate Ellipsoidal Quantum Dots in Presence of Electrical and Magnetic Fields

In framework of the adiabatic approximation the energy states of electron as well as direct light absorption are investigated in strongly oblate and strongly prolate ellipsoidal quantum dots (QDs) at presence of electric and magnetic fields. Analytical expressions for particle energy spectrum are obtained. The dependence of energy levels’ configuration on QD geometrical parameters and field intensities is analytically obtained. The energy levels of electrons are shown to be equidistant both for strongly oblate and prolate QDs. The effect of the external fields on direct light absorption of a QD was investigated. The dependence of the absorption edge on geometrical parameters of QDs and intensities of the electric and magnetic fields is obtained. Selection rules are obtained at presence as well as absence of external electric and magnetic fields. In particular, it is shown that the presence of the electric field cancels the quantum numbers selection rules at the field direction, whereas in radial direction the selection rules are preserved. Perspectives of practical applications for device manufacturing based on ellipsoidal quantum dots are outlined.

Direct Interband Light Absorption in Strongly Prolated Ellipsoidal Quantum Dots’ Ensemble

Within the framework of adiabatic approximation, the energy levels and direct interband light absorption in a strongly prolated ellipsoidal quantum dot are studied. Analytical expressions for the particle energy spectrum and absorption threshold frequencies in three regimes of quantization are obtained. Selection rules for quantum transitions are revealed. Absorption edge and absorption coefficient for three regimes of size quantization (SQ) are also considered. To facilitate the comparison of obtained results with the probable experimental data, size dispersion distribution of growing quantum dots by the small semiaxe in the regimes of strong and weak SQ by two experimentally realizing distribution functions have been taken into account. Distribution functions of Lifshits–Slezov and Gaussian have been considered.

Electronic States and Light Absorption in a Cylindrical Quantum Dot Having Thin Falciform Cross Section

Energy level structure and direct light absorption in a cylindrical quantum dot (CQD), having thin falciform cross section, are studied within the framework of the adiabatic approximation. An analytical expression for the energy spectrum of the particle is obtained. For the one-dimensional “fast” subsystem, an oscillatory dependence of the wave function amplitude on the cross section parameters is revealed. For treatment of the “slow” subsystem, parabolic and modified Pöschl-Teller effective potentials are used. It is shown that the low-energy levels of the spectrum are equidistant. In the strong quantization regime, the absorption coefficient and edge frequencies are calculated. Selection rules for the corresponding quantum transitions are obtained.

Direct interband light absorption in a strongly oblated ellipsoidal quantum dot

Within the framework of adiabatic approximation the energy levels and direct interband light absorption in a strongly oblated ellipsoidal quantum dot are studied. Analytical expressions for the particle energy spectrum and for the absorption threshold frequencies at three regimes of quantization are obtained. Selection rules for quantum transitions are revealed.

Impurity states in a cylindrical quantum dot with the modified Pöschl-Teller potential

We study impurity states in a cylindrical quantum dot with two confining potentials: in the direction of cylinder axis modified Pöschl-Teller potential and in radial direction parabolic potential. Studies of impurity states are performed in the frames of variational method and by using numerical methods, the dependences of the particle energy on the geometrical parameters of the cylindrical quantum dot are derived. Dependences of the electron binding energy on the half-width and depth of the potential wall are revealed.

On the possibility of implementation of Kohn’s theorem in the case of ellipsoidal quantum dots

An electron gas in a strongly oblated ellipsoidal quantum dot with impenetrable walls is considered. Influence of the walls of the quantum dot is assumed to be so strong in the direction of the minor axis (the OZ axis) that the Coulomb interaction between electrons in this direction can be neglected and considered as two-dimensional, coupled. On the basis of geometric adiabaticity we show that in the case of a few-particle gas a powerful repulsive potential of the quantum dot walls has a parabolic form and localizes the dot in the geometric center of the structure. Due to this fact, conditions occur to implement the generalized Kohn theorem for this system.

Electronic states in a cylindrical quantum dot with the modified Pöschl-Teller potential in the presence of external magnetic field

Energy levels of an electron in a cylindrical quantum dot with a modified Pöschl-Teller potential in the presence of external homogeneous magnetic field are studied. Analytical expressions for the wave function and energy of the particle are obtained. Different regimes of magnetic quantization are considered and peculiarities of behavior of the electron energy spectrum depending on the value of applied magnetic field are revealed.

Adiabatic description of impenetrable particles in an infinitely deep potential well

In the framework of adiabatic approximation the energy spectrum and wave functions of two impenetrable particles in an infinitely deep potential well are considered for two cases of approximation of the effective confining potential of the “slow” subsystem. In case of the quadraticterm approximation the obtained energy spectrum is equidistant. The probability distribution in the range of “fast” particle has a symmetric shape while that in the range of the “slow” particle is asymmetric and the peak of localization of the system in its ground state is shifted towards the “fast” particle. In the first excited state the center of the probability distribution of the “slow” particle is shifted towards the impenetrable wall.

Optical properties of biexcitons in ellipsoidal quantum dot

The optical properties of biexciton and exciton states in strongly oblate ellipsoidal quantum dot are investigated in the framework of variational method. The trial wave function for the biexciton is constructed on the base of one-particle wave functions. The dependencies of the photoluminescence spectra for the crossover states of biexciton and exciton are constructed as a function of the incident light energy. The peak position of the photoluminescence spectra for biexciton and exciton are revealed. The oscillator strength of biexciton and exciton are calculated. The biexciton’s and exciton’s radiative lifetimes in strongly oblate ellipsoidal quantum dot are estimated.

Three-layer antireflection diamond-like carbon films on glass

The three-layer diamond-like carbon films grown on the glass from the decomposition of toluene and nitrogen by Plasma Enhanced Chemical Vapor Deposition technique. The optimal parameters of three-layered structures with the minimum reflection in the range of 400–750 nm were theoretically calculated using the generalized transfer-matrix technique. The dependence of the refractive index of grown films on the plasma power and nitrogen concentration in the gas mixture was investigated.