Influence of temperature on ground state energy of bound polaron in asymmetric Gaussian potential quantum well in presence of electromagnetic field

By a combination method of Lee–Low–Pines unitary transformation method and Pekar-type variational method, the ground state energy (GSE) of the bound polaron is studied in the asymmetrical Gaussian potential quantum well considering the temperature and electromagnetic field. The impacts of the temperature and asymmetrical Gaussian potential, electromagnetic field and phonon–electron coupling upon the GSE are obtained. The results show that the GSE of the bound polaron not only oscillates as the temperature changes regardless of the electromagnetic field and asymmetrical Gaussian potential and Coulomb impurity potential (CIP) and electron–phonon coupling but also has different rules with the electromagnetic field and asymmetrical Gaussian potential and CIP and electron–phonon coupling at different temperature zones.     

Impurity-related optical response in a 2D and 3D quantum dot with Gaussian confinement under intense laser field

ABSTRACT

Using the two-dimensional (2D) diagonalisation method, the impurity-related electronic states and optical response in a 2D quantum dot with Gaussian confinement potential under nonresonant intense laser field are investigated. The effects of a hydrogenic impurity on the energy spectrum and binding energy of the electron and also intersubband optical absorption are calculated. The obtained numerical results show that the degeneracies of the excited electron states are broken and the absorption spectrum exhibits a redshift with the values of the laser field. The findings indicate a new degree of freedom to tune the performance of novel optoelectronic devices, based on the quantum dots and to control their specific properties by means of intense laser field and hydrogenic donor impurity. Using the same Gaussian confinement model, the electronic properties of a confined electron in the region of a spherical quantum dot are studied under the combined effects of on-centre donor impurity and a linearly polarised intense laser radiation. The three-dimensional problem is used to theoretically model, with very good agreement, some experimental findings reported in the literature related to the photoluminescence peak energy transition.     

The polaron effect on the binding energy of a shallow donor impurity in quantum-well wires in an electric field

Using a variational technique, the effect of electron-longitudinal optical (LO) phonon interaction on the ground and the first few excited states of a hydrogenic impurity in a semiconductor quantum wire of rectangular cross section under an external electric field is studied theoretically for the impurity atom doped at various positions. The results for the binding energy as well as polaronic correction are obtained as a function of the size of the wire, the applied uniform electric field and the position of the impurity. It is found that the presence of optical phonons changes significantly the values of the impurity binding energies of the system. Taking into account the electron–LO phonon interaction the 1s→2p_y and 1s→2p_z transition energies are calculated as a function of applied electric field for different impurity positions.     

The bound one-dimensional “relativistic” polaron in a one-loop approximation

A quasirelativistic model of the narrow-gap semiconductor is considered. The interaction of the Dirac electron field with the non-dispersive phonon field in the short-range external potential (impurity) is taken into account. The classical solutions corresponding to the discrete spectrum are found. The fermion vacuum polarization effect is studied within the one-loop approximation.     

Optical properties of a hydrogenic impurity in a confined Zn1−xCdxSe/ZnSe spherical quantum dot

The effect of longitudinal optical phonon field on the ground state and low lying-excited state energies of a hydrogenic impurity in a Zn_1−xCd_xSe/ZnSe strained quantum dot is investigated for various Cd content using the Aldrich-Bajaj effective potential. We consider the strain effect considering the internal electric field induced by the spontaneous and piezoelectric polarizations. Calculations have been performed using Bessel function as an orthonormal basis for different confinement potentials of barrier height. Polaron induced photoionization cross section of the hydrogenic impurity in the quantum dot is investigated. We study the oscillator strengths, the linear and third-order nonlinear optical absorption coefficients as a function of incident photon energy for 1s-1p and 1p-1d transitions with and without the polaronic effect. It is observed that the potential taking into account the effects of phonon makes the binding energies more than the obtained results using a Coulomb potential screened by a static dielectric constant and the optical properties of hydrogenic impurity in a quantum dot are strongly affected by the confining potential and the radii. It is also observed that the magnitude of the absorption coefficients increases for the transitions between higher levels with the inclusion of phonon effect.     

Polaronic Effects on the Impurity Binding Energy in a Polar Crystal Slab Within an Electric Field

The effects of the interaction between electron and bulk longitudinal optical (LO) phonon and surface optical (SO) phonon on the impurity binding energy of the ground state in a polar crystal slab within an external electric field are derived by using the method of a variational wavefunction. The binding energy of the bound polaron is obtained as a function of the impurity position, the slab thickness and the electric field strength. It is found that the polaronic correction to the impurity binding energy by the SO phonon may be enhanced and that by the LO phonon may be reduced with increasing electric field strength. And the effect of the electron-phonon interaction is quite important in increasing the values of binding energy.     

The properties of one-dimensional quasiperiodic lattice's phonon spectrum

A numerical method with renormalization group transformation is used to study the scaling properties of phonon spectrum and its relevant state of one-dimensional quasiperiodic lattice which is constructed by reduced map. We find that the phonon spectrum at finite gaps' edges in the binary chain Fibonacci model is a Cantor-like set spectrum. The spectrum is singularly continuous and the state is a critical state.     

Spatial distribution of local density of states in vicinity of impurity on semiconductor surface

We present the results of detailed theoretical investigations of changes in local density of total electronic surface states in 2D anisotropic atomic semiconductor lattice in vicinity of impurity atom for a wide range of applied bias voltage. We have found that taking into account changes in density of continuous spectrum states leads to the formation of a downfall at the particular value of applied voltage when we are interested in the density of states above the impurity atom or even to a series of downfalls for the fixed value of the distance from the impurity. The behaviour of local density of states with increasing of the distance from impurity along the chain differs from behaviour in the direction perpendicular to the chain. The article is published in the original.     

Modification of Mössbauer reflection spectra of group AIIBVI single crystals with Fe<Superscript>57</Superscript> nuclei under influence of infrared radiation

Interaction of Mössbauer gamma radiation with ultrasound vibrations in group AIIBVI single crystals of CdS and CdSe with Fe⁵⁷ impurity nuclei under action of infrared radiation is investigated. It is shown that the infrared irradiation excites a phonon field in single crystals. Similar to the case of optical irradiation of single crystals the shape of their Mössbauer spectrum is modified. The effect of double modulation of resonant gamma radiation by infrared radiation has been observed.     

Effects of electric field and size on the electron-phonon interaction in a spherical quantum dot with impurity

The effects of electric field and size on the electron-phonon interaction with an on-center impurity in a Zn_1?x Cd _x Se/ZnSe spherical quantum dot are studied, taking into account the interactions with confined, half-space and surface optical phonons. In addition, the interaction between impurity and phonons has also been considered. The results show that the electron-confined, electron-half-space, and electron-surface optical phonon interaction energies are all negative. The electron-confined optical phonon interaction energy is weakened by the electric field, but the electron-half-space and electron-surface optical phonon interaction energies are strengthened by it. In particular, the electron-surface optical phonon interaction depends strongly on the electric field, and it will vanish when the electric field is absent. It is also found that the electron-confined optical phonon interaction and electron-impurity “exchange” interaction energies reach a peak values as the quantum dot radius increases and then gradually decrease, but the electron-half-space optical phonon interaction energy exponentially quickly approaches 0 as the quantum dot radius increases.     

Isotherms of thermal conductivity in PbTe-MnTe solid solutions

The temperature dependences of the thermal conductivity λ of PbTe-MnTe solid solutions (0–4 mol % MnTe) are measured in the range 170–670 K. The data obtained are used in constructing the isotherms of the lattice thermal conductivity λ_l and in estimating the effective cross section for phonon scattering by Mn impurity atoms. It is found that all the isotherms exhibit an anomalous increase in λ_l in the concentration range 1.25–2.0 mol % MnTe, which disagrees with the usually observed decrease in λ_l with an increase in the impurity concentration. It is assumed that the anomalous increase in λ_l manifests itself after attainment of the percolation threshold when a continuous chain of overlapping deformation fields produced by individual atoms (an infinite cluster) is formed in the crystal. In the crystal lattice, stresses are partly compensated and phonon scattering decreases. The assumption is made that the effect observed has a universal character.     

Impurity states of electrons in quantum dots in external magnetic fields

The influence of isolated impurity atoms on the electron energy spectrum in a parabolic quantum dot in quantizing magnetic field is studied. The impurity potential is approximated by a Gaussian separable operator which allows one to obtain the exact solution of the problem. We demonstrate that in the electron energy spectrum there is a set of local levels which are split from the Landau zone boundaries in the upward or downward direction depending on the impurity type. We have calculated the local level positions, the wave functions of electrons in bound states, and the residues of the electron scattering amplitudes by impurity atoms at the poles.     

SiC电子输运特性的Monte Carlo数值模拟

利用系综MonteCarlo法研究了2H ,4H和6HSiC的电子输运特性.在模拟中考虑了对其输运过程有着重要影响的声学声子形变势散射、极化光学声子散射、谷间声子散射、电离杂质散射以及中性杂质散射.通过计算,获得了低场下这几种不同SiC多型电子迁移率同温度的关系,并以4H SiC为例,重点分析了中性杂质散射的影响.最后对高场下电子漂移速度的稳态和瞬态变化规律进行了研究.将模拟结果同已有的实验数据进行了比较,发现当阶跃电场强度为10×106V·cm-1时,4H Sic电子横向瞬态速度峰值接近33×107cm·s^-1,6H Sic接近30×107cm·s^-1.     

Effect of hydrostatic pressure on the phonon spectrum of PbIn alloys using electron tunneling

The effect of hydrostatic pressure on the phonon spectrum of PbIn alloys has been studied. A shift to higher frequencies of the transverse, longitudinal and impurity band peaks is observed as well as a reduction in amplitude.     

On the thermodynamics of a degenerate two-dimensional electron gas in a strong magnetic field: density of states

Systematic expansions, in powers ofB ^–1, for the free energy and the density of states, are derived for a two-dimensional degenerate electron gas in the presence of a strong magnetic field and an arbitrary potential. They are then applied to a system involving random impurities. Landau levels are shown to be broadened, with level widths related to the impurity concentration and potential. We show that level broadenings, induced by long range electron-impurity ineractions, do not depend on the magnetic field in the strong field limit, confirming the existing theories. But broadened Landau levels can have a large variety of shapes as one changes the impurity potential, distribution and concentration. Our theory, with a Gaussian potential, leads to a good agreement with the recent experiment on the de Haas-van Alphen effect in Br₂-graphite intercalation compounds     

Frequency spectra of one-dimensional lattices with impurities distributed at random

The phonon frequency spectrum has been calculated for a linear atomic chain doped at random with atoms of another mass and bound with another force constant than the host chain. Narrow bands above the maximum frequency of the undisturbed chain as well as peaks superimposed on the spectrum have been found and are discussed.     

On the spectrum of the dynamical matrix for a class of disordered harmonic systems

We study some aspects of the effect of mass disorder on the spectrum of the dynamical matrix of an infinite crystal in the harmonic approximation. Under suitable conditions on the masses, it is shown that the spectrum contains an absolutely continuous part and a nonempty set of isolated point eigenvalues of finite multiplicity whose number is smaller than or equal to the number of impurity atoms if the latter is finite. These conditions are satisfied only in the limiting case of zero concentration of each species of impurity. We draw some conjectures and make remarks on the spectrum under less restrictive conditions on the masses and briefly compare them with known results for random harmonic systems.Supported in part by the Swiss National Fund (to M.R.) and the Eidgenössische Stipendienkommission für ausländische Studierende (to W. F. W.).     

Effect of impurity on the absorption of a parabolic quantum dot with including Rashba spin–orbit interaction

In this paper, the influence of impurity parameters on the electron energy spectrum and absorption coefficients in a parabolic quantum dot and in the presence of Rashba spin–orbit interaction subjected to a perpendicular magnetic field is studied. The impurity potential is approximated by a Gaussian form. We have shown that in the both cases of a repulsive and attractive Gaussian impurity, the absorption coefficients are strongly affected by the decay length. These coefficients show blue (red) shift as the decay length of repulsive (attractive) impurity is increased. The dependence of the absorption coefficients on the impurity position is also examined for different polarizations. Our results show that the absorption coefficient has local maximum (minimum) for a given value of impurity position for Y-polarized (X-polarized) light.     

Thermal 1/ω fluctuations of a quantum oscillator under a parametric effect of a random field

It is shown that the effect of a time-correlated Gaussian random field of sufficiently high intensity on the elasticity coefficient of a quantum oscillator manifests itself in the generation of thermal fluctuations with a 1/ω spectrum in the oscillator. It is also shown that, in any physical system described by the equation of an anharmonic oscillator, fluctuations with a 1/ω spectrum arise at an above-critical temperature.     

The bound polaron in an electric field in polar semiconductor heterostructures

We have calculated the ionization energy of a bound polaron confined in general step quantum wells (QWs) in the presence of an electric field, in which the coupling of an electron with confined bulk-like LO phonons, half-space LO phonons and interface phonons is considered. In particular, the interaction of the impurity with the various phonon modes is also included in QWs. Results have been obtained as a function of the barrier height, the well width, the electric field intensities and the position coordinates of the impurity in the QWs. Our numerical calculations clearly show that the interaction between the impurity and the phonon field plays an important role in screening the Coulomb interaction. It is shown that the cumulative effect of the electron–phonon coupling and the impurity–phonon coupling can contribute appreciably to the donor ionization energy. Only for a certain range of well widths can we neglect all the polaronic effects.