Arshak L. Vartanian

Electron interaction with confined and interface polar optical phonons and electron mobility in quantum wires

Abstract The electron scattering in a cylindrical quantum wire embedded in a dielectric medium is studied by taking into account the phonon confinement effect. Expressions for intrasubband scattering rates have been obtained previously. Here using the Born approximation we obtain analytical expressions for intersubband scattering rates as well. Taking into account an inelasticity of the electron–phonon interaction the expressions for electron relaxation time and mobility are also derived. The predomination regions of different phonon modes and the phonon confinement effect on the scattering rate for intrasubband transitions are found. It is shown that the consideration of phonon confinement leads to mobility increase.

Phonon confinement effect on the polaron basic parameters in nanowires in the presence of external fields

The effect of electric and magnetic fields on the basic parameters of confined and interface polarons in cylindrical nanowires embedded in a non-polar matrix are studied theoretically for the first time. The analytical expressions for the quasi-one-dimensional Frohlich polaron self-energy and effective mass are obtained as functions of the wire radius and the strength of the external fields; this can be used in the interpretation of optical phenomena related to polaron motion in cylindrical nanowire when the effect of applied fields competes with the spatial quantum confinement.

Mobility Calculation of Quasi-Two-Dimensional Electron Gas by the Energy Loss Method

The energy loss method for mobility calculation in low-dimensional semiconductor structures with quasi-two-dimensional gas of charge carriers is developed. For scattering by charged impurities a mobility expression is found which depends on quantum well characteristics, the form of the impurity center distribution within a well and surroundings, and also on the dielectric constant of the system under consideration. The method is also used for mobility calculation in the case of interface roughness and alloy disorder scattering in a quantum well. It is shown that taking account of interface roughness scattering at near to room temperature improves considerably the agreement between the theory and experiment.

Polaronic shift of the Wannier-Mott exciton binding energy in a quantum wire with allowance for the phonon confinement effect

Within the framework of the Li-Low-Pines model the interaction of a Wannier-Mott exciton with polar optical phonons in a cylindrical semiconductor wire is studied, taking into account the phonon confinement effect. An analytical expression for the exciton binding energy with allowance for the polaronic effect is obtained. Numerical calculations of the binding energy are carried out for AlAs/GaAs/AlAs and ZnSe/CdSe/ZnSe wires with a various degree of polarity of quantum wire materials. The polaronic shift of the binding energy of light and heavy hole excitons is calculated.

Impurity-Bound Polaronic States in ZnSe Quantum Dots Under Electric Field: Image Charge Effect

A Landau–Pekar variational approach is used to study the ground and first excited states of an impurity-bound polaron in a ZnSe quantum dot under an external electric field, by taking into account the image charge effect (ICE). The binding energy (BE) of the donor impurity is calculated considering the interaction of an electron with both the bulk-type longitudinal optical phonons and the interface optical phonons. Both electric field and parabolic confinement effects on the BE and its polaronic shift for 1s and 2s hydrogen-like states with and without ICE are investigated in detail. We have shown that the ICE strongly reduces the donor BEs in both ignoring and considering electron–optical phonon interaction.

Confined acoustic phonon-mediated spin relaxation in a twodimensional quantum dot in the presence of perpendicular magnetic field

The spin-relaxation time due to the electron-acoustic phonon scattering in GaAs quantum dots is studied after the exact diagonalization of the electron Hamiltonian with the spin-orbit coupling. It has been shown that in comparison with flexural phonons, the electron coupling with the dilatational phonons causes 3 orders faster spin relaxation. We have found that the relaxation rate of the spin-flip is an order of magnitude smaller than that of the spin- conserving.

The influence of electric field on the quasi-confined and interface polaron basic parameters in a wurtzite nitride quantum wire

The influence of an external electric field on the quasi-confined and interface Frohlich polaron basic parameters in a wurtzite nitride cylindrical quantum wire embedded in a non-polar matrix is studied theoretically. By using the Lee-Low-Pines variational approach, the dependences of the polaron self-energy and effective mass are obtained as functions of the wire radius and the strength of the electric field. The contributions of different phonon modes to the polaron basic parameters are estimated.

Electron capture processes in quantum dots due to one-and two-phonon assisted transitions: The role of optical phonon confinement

Electron capture induced by carrier heating in spherical quantum dot-quantum well (QD-QW) structure is studied theoretically. The capture rate (CR) in one- and two-polar- optical-phonon-mediated capture processes has been studied by taking into account the phonon confinement. We have derived the analytic expressions for carrier CRs which can be conveniently applied to practical calculations for the spherical quantum dot systems. The numerical results of the CR as function of dot radius, lattice temperature and electron density in GaAs/AlAs/vacuum and CdSe/ZnS/H2O QD systems are obtained and discussed.

Effect of Phonon Confinement on Optical Phonon-Mediated Carrier Capture into CdSe/ZnS Quantum Dots

Electron capture induced by carrier heating in the CdSe/ZnS spherical quantum dot–quantum well structure is studied theoretically. The capture rate has been calculated by taking into account the phonon confinement effect. Numerical results for the capture rate as a function of dot radius, lattice temperature, and electron density in the CdSe/ZnS/H2O quantum dot (QD) system are obtained and discussed. It has been shown that the capture rate of an electron from the barrier region to the quantum dot ground state due to the emission of confined or interface optical phonons exhibits strong resonances versus dot radius. Our results reveal that the capture time is larger than 1 ns across broad ranges of quantum dot radius. We have found the increase of the capture rate due to emission of LO1 as well as IO/SO phonons with increasing temperature. However, for structures with lower electron densities (n ≤ 1016 cm−3), the monotonic behavior of the capture rate in case of IO/SO phonon interactions is broken and a local maximum in the temperature dependence appears. In contrast to the GaAs/AlAs spherical quantum dot–quantum well structure, the capture rate in CdSe/ZnS/H2O QDs is very strongly dependent on the electron density.

The Phonon Confinement Effect on the Impurity States in Cylindrical Nanowire with a Finite Confining Potential in Presence of Electric and Magnetic Fields

In the framework of effective mass approximation, the LandauPekar variational procedure is adopted to study the ground-state binding energy of a hydrogenic impurity in a semiconductor nanowire with finite confining potential subjected to both external fields (electric and magnetic) and electronpolar optical phonon interaction taking into account the phonon confinement effect. The results for the binding energy as well as polaronic correction are obtained as a function of the wire radius, impurity position and applied fields. Calculated results reveal that the values of the polaronic shifts of impurity binding energy can be quite different for cases with finite and infinite confining potentials.