透镜型量子点中类氢杂质基态能的计算

通过有效质量近似和变分法，研究了垂直磁场下透镜型量子点中类氢杂质基态能量，并与球型量子点进行了比较.研究表明：对于球型量子点，基态能仅与杂质的偏离距离有关，与垂直和水平偏离无关；而对于透镜型量子点，由于水平方向和垂直方向束缚势的非对称性，电子基态能不仅与杂质的偏离距离有关，还与杂质偏离方向有关. 关键词： 透镜型量子点 基态能 变分法     

Far infrared impurity absorption in a quantum well

We have calculated the energy and lineshape of the 1s → 2p_x,y transition for a hydrogenic impurity located in a quantum well. Due to the dependence of the transition energy on the impurity location, the absorption lineshape is very sensitive to the doping profile. The spectrum, in general, exhibits two peaks, arising from impurities located near the center and the edges of the well.     

GaAs基InAs量子点中类氢杂质的束缚能

在有效质量近似下,采用微扰法研究了InAs/GaAs量子点内类氢杂质基态及低激发态的束缚能.受限势采用抛物形势,在二维平面极坐标下,精确地求解了电子的薛定谔方程.数值计算结果表明,类氢杂质基态及低激发态的束缚能敏感地依赖于抛物形势的角频率,受类氢杂质的影响,谱线发生蓝移.这一结果对设计和制备量子点器件是有价值的.     

Binding energy of a hydrogen-like donor impurity in a quantum well-wire in magnetic and electric fields

The effect of a longitudinal magnetic and a transverse electric fields on the binding energy of a hydrogen-like donor impurity is studied for a semiconductor quantum well-wire approximated by a cylindrical well of finite depth. It is shown that the magnetic and electric fields as well as the impurity distance from the wire axis are the effective tools for the influence on the binding energy.     

The binding energy of hydrogen-like impurity in quantum dots with convex bottom in magnetic field

Within the framework of effective mass approximation and variational method, the electronic and impurity states in spherical quantum dots with convex bottom in magnetic field are calculated. Calculations are carried out both for on-center and off-center impurities. The impurity binding energy dependencies on radius, measure of convexity of quantum dot bottom, impurity position and magnetic field induction are obtained for the Ga_1-xAl_xAs/Ga_1-yAl_yAs system.     

The effects of magnetic field and hydrogen-like impurity on RbCl quantum pseudodot qubit

By using a variational method of Pekar type, we investigate the effects of the hydrogen-like impurity and magnetic field on the electron’s probability density (PD) and oscillating frequency (OF) of a RbCl quantum pseudodot qubit. Numerical results indicate that (1) the PD oscillates periodically; (2) the crest of the PD will decrease with increasing the cyclotron frequencies and the Coulombic impurity potential strength; (3) as the cyclotron frequency of the magnetic field and the strength of the Coulombic impurity potential increases, PD’s peaks will occur more frequently; (4) besides, Figs. 1b and 2b clearly show that in a single period the PD will decrease with increasing the cyclotron frequency and the Coulombic impurity potential strength when \( t > 1.8\;\text{fs} \); whereas the changing law is just the opposite when \( t < 1.8\;\text{fs} \); (5) the OF is an aggrandizing function of the strength of the Coulombic impurity potential, whereas it is a decaying one of the cyclotron frequencies of the magnetic field. The coherence of qubit is crucial to the investigations of quantum information and quantum computation, where the electron’s PD, the OF and the coherence time are the physical quantities representing the properties of coherence. Our research results fine that by changing the cyclotron frequency of the magnetic field and the strength of the Coulombic impurity potential one can adjust the electron’s PD and the OF.

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Fig. 1 The PD \( \text{Q}\left( {r,t} \right) \) versus the time \( t \) and the cyclotron frequency of the magnetic field \( \omega_{c} \) with \( \text{V}_{0} = 10.0\,\text{meV, r}_{0} = 1.0\,\text{nm, }\beta \text{ = 1.0}\,\text{meV} \cdot \text{nm} \) and \( x = y = z = 1.0\,\text{nm} \)

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Fig. 2 The PD \( \text{Q}\left( {r,t} \right) \) versus the time \( t \) and strength of the Coulombic impurity potential \( \beta \) with \( \text{V}_{0} = 10.0\,\text{meV, r}_{0} = 1.0\,\text{nm,} \, \omega_{c} \text{ = 2.0}\, \times \text{10}^{13}\,\text{Hz} \) and \( x = y = z = 1.0\,\text{nm} \)

     

Binding energy and photoionization cross-section of a hydrogen-like donor impurity in a quantum well-wire in a magnetic field

The effect of a uniform longitudinal magnetic field on the binding energy and photoionization cross-section of a hydrogen-like donor impurity is studied for a semiconductor quantum well-wire approximated by a cylindrical well of finite depth. The selection rules and analytical expressions for the photoionization cross-section are obtained depending on the magnetic field induction, impurity position, and light wave polarization.     

Intense laser field effect on impurity states in a semiconductor quantum well: transition from the single to double quantum well potential

In this work are studied the intense laser effects on the impurity states in GaAs-Ga_{1− x} Al _x As quantum wells under applied electric and magnetic fields. The electric field is taken oriented along the growth direction of the quantum well whereas the magnetic field is considered to be in-plane. The calculations are made within the effective mass and parabolic band approximations. The intense laser effects have been included through the Floquet method by modifying the confinement potential associated to the heterostructure. The results are presented for several configurations of the dimensions of the quantum well, the position of the impurity atom, the applied electric and magnetic fields, and the incident intense laser radiation. The results suggest that for fixed geometry setups in the system, the binding energy is a decreasing function of the electric field intensity while a dual monotonic behavior is detected when it varies with the magnitude of an applied magnetic field, according to the intensity of the laser field radiation.     

Magnetic-field dependence of hydrogenic impurity states in a quantum well wire

Summary The binding energy for on-centre impurities in a rectangular quantum well wire is calculated as a function of the width of the wire and perpendicular magnetic field. The results for zero-magnetic-field case are in perfect agreement with previous calculations. The authors of this paper have agreed to not receive the proofs for correction.     

Shallow impurity centers in semiconductor quantum well structures

Interest in the study of the behavior of shallow impurity centers in superlattices and quantum well structures is fairly recent. This paper reviews briefly both the theoretical and experimental work done in this field in the last few years. Several recent calculations of the energy levels of hydrogenic impurity states in quantum well structures, such as Ga_1?xAl_xAsGaAsGa_1?xAl_xAs, are reviewed. The behavior of these levels as a function of the quantum well size is discussed. Recent experimental data concerning the variations of the binding energies of shallow donors and acceptors as a function of the GaAs quantum well size are reviewed. A comparison between these experimental measurements and the results of recent calculations is presented.     

Magnetic impurity interactions in a quantum well on the base of IV-VI semiconductors

We study the indirect exchange interaction of magnetic impurities via 2D excitations in a quantum well on the base of IV-VI narrow-gap semiconductors. The energy spectrum of 2D excitations takes into account the nonparabolicity of dispersion as well as the strong spin-orbit interaction. The calculations are performed for the case when the main mechanism is an exchange by virtual electron-hole pairs. It means that we assume the Fermi level to lie inside the energy gap, and the temperature to be small, T << ϵ₀. It is shown that at large distances. R >> ν/ϵ₀ (2ϵ₀ is the excitation energy for nearest size-quantized subbands, ϵ the interband interaction parameter), the antiferromagnetic interaction of pairs dominates, so that the impurity spins tend to be directed along the heterojunction plane perpendicular to the vector connecting the impurities. The interaction contains both the Heisenberg and pseudodipole terms.     

Temperature and hydrogen-like impurity effects on the excited state of the strong coupling bound polaron in a CsI quantum pseudodot

With hydrogen-like impurity(HLI) located in the center of Cs I quantum pseudodot(QPD) and by using the variational method of Pekar type(VMPT), we investigate the first-excited state energy(FESE), excitation energy and transition frequency of the strongly-coupled bound polaron in the present paper. Temperature effects on bound polaron properties are calculated by employing the quantum statistical theory(QST). According to the present work's numerical results, the FESE, excitation energy and transition frequency decay(amplify) with raising temperature in the regime of lower(higher)temperature. They are decreasing functions of Coulomb impurity potential strength.     

Infra-red free-carrier absorption due to impurity scattering in semiconducting quantum well structures

The theory of free-carrier absorption (FCA) is developed, in the extreme quantum limit when the carriers are assumed to populate only the lowest quantized energy level, for quasi-two and one-dimensional semiconducting quantum well structures where the carriers are scattered by ionized impurities. The radiation field is assumed to be polarized in the plane of the layer in the quasi-two-dimensional case and along the length of the wire in the quasi-one-dimensional case. Expressions for FCA are obtained for the cases where the impurities are either in the well (background impurities) or outside the well (remote impurities). Variation of FCA is numerically studied with photon frequency and well width.     

Adiabatic, closed-form approach to the highly efficient analysis of a fiber Raman amplifier problem

We propose a novel framework for the solution of a general fiber Raman amplifier problem by use of a closed integral form of a Raman equation. Treating the given problem as an adiabatic system and taking the Raman process as the perturbation parameter, we can seek the solution along the iteration axis rather than the fiber propagation axis, permitting an orders-of-magnitude increase for the product of convergence speed and spatial resolution in the numerical assessment.     

Electronic states of a hydrogenic impurity in a zinc-blende GaN/AlGaN quantum well

Binding energies of ground and a few low lying excited states of a hydrogenic donor confined in a zinc-blende GaN/AlGaN quantum well are investigated. They are computed within the framework of single band effective mass approximation, by means of a variational approach. The donor states are investigated with the various impurity positions as a function of well width. The calculations have been carried out with the inclusion of conduction band non-parabolicity through the energy dependent effective mass. The variational solutions have been improved by using a two-parametric trial wavefunction. The results seem better and good agreement with the other investigators. To support our results, we observe that the values of variational parameters are consistent when two parameter wave function is used. We find that the inclusion of non-parabolic effects leads to more binding for all the values of well width and is significant for narrow wells. The results are compared with the existing available literature.     

A non-conventional approach to study the quenched impurity effects on quantum criticality

A non-conventional point of view is used to explore the still unclear role played by the competition between quenched disorder and quantum fluctuations in systems which exhibit a quantum phase transition in the clean limit. The approach consists in averaging over quantum degrees of freedom and next in applying the renormalization group transformation to the resulting effective classical random action. It emerges that, below four dimensions, the quantum criticality appears to be controlled by the classical random fixed point.