The electronic structure of a quantum well under an applied electric field

The effects of an applied electric field on quantum well subband energies are calculated variationally within the effective mass approximation for model potential profiles. The concept of a quasi-bound state is examined critically. For higher electric field values it is shown that the quasi-bound state approximation for the ground and first excited state of the electron, and for the ground state of the hole is valid.     

Donor electron in a quantum well under the influence of an electric field

The ionization energies and the polarizabilities of a donor in an isolated well of a quasi two dimensional (Q2D) GaAs/Ga_1−x Al _x As heterostructure have been obtained for different well widths including electron-lattice coupling. A wave function that properly reduces to the hydrogenic function in the limiting case has been used. For fields of the order of 10⁵ V/m, the ionization energies decrease slightly with electric fields for all well widths (10 nm to 50 nm) studied. Also for a given electric field, as the well width increases, the ionization energy decreases. For fields of the order of 10⁷ V/m and for smaller well widths (<10 nm), the ionization energy generally increases with electric field. The results also show that for electric fields of this order, no donor bound state associated with the lowest subband is possible for well widths greater than 20 nm. The polarizabilities estimated using the expression for the dipole operator show that as the well width increases, the polarizability values also increase and do not show any abnormal behaviour.     

Tunneling from a 3-dimensional quantum well in an electric field: an analytic solution

We derive the stationary tunneling solution for charged particles moving in a spherical, 3-dimensional zero-range potential plus a constant electric field. From the analytic expression for the wave function we calculate the distribution of the current inside and outside the vacuum barrier. At low field strengths there is a constant spreading of the tunnel current orthogonal to the direction of the applied field. At intermediate field strengths the exact results for the current distribution behave different from the semiclassical predictions.     

Excitonic transitions in Be-doped GaAs/AlAs multiple quantum well

A series of GaAs/AlAs multiple-quantum wells doped with Be is grown by molecular beam epitaxy. The photoluminescence spectra are measured at 4, 20, 40, 80, 120, and 200 K, respectively. The recombination transition emission of heavy-hole and light-hole free excitons is clearly observed and the transition energies are measured with different quantum well widths. In addition, a theoretical model of excitonic states in the quantum wells is used, in which the symmetry of the component of the exciton wave function representing the relative motion is allowed to vary between the two- and threedimensional limits. Then, within the effective mass and envelope function approximation, the recombination transition energies of the heavy- and light-hole excitons in GaAs/AlAs multiple-quantum wells are calculated each as a function of quantum well width by the shooting method and variational principle with two variational parameters. The results show that the excitons are neither 2D nor 3D like, but are in between in character and that the theoretical calculation is in good agreement with the experimental results.     

Carrier energy spectrum and lifetime in quantum dots in electric field

The S-matrix formalism is used to perform analytical calculations of the spectrum of quasi-stationary states of charge carriers in a core-shell quantum dot. Analytical expressions are obtained for the second-order perturbative corrections to the position and half-width of a quasi-stationary energy level, and level shifts are calculated numerically for a core-shell quantum dot in the presence of an electrostatic field. The corrections to level half-width due to Stark effect are analyzed as functions of level energy and barrier thickness. It is shown that there exists a level position E _cr such that the correction δΓ to the level half-width changes sign. An analytical expression for the quadratic Stark shift in a dc-biased quantum well is found in semiclassical approximation. It is shown that the corresponding correction δΓ to half-width also changes sign as energy passes through E _cr. As an example, the Stark shift is calculated for a core-shell quantum dot in the electrostatic field of an adjacent protein molecule.     

Double quantum well electronic energy spectrum within a tilted magnetic field

The analytical solutions of the Schrödinger equation for a double quantum well structure (DQWS) subjected to an externally applied tilted magnetic field are obtained and the results are discussed. The dependency of the energy spectrum of the system on the applied magnetic field direction is also given.     

Excitonic transitions in GaAs---GaAlAs superlattices under a weak electric field

We report a study of the photoluminescence spectra of GaAs---Ga_0.65Al_0.35As superlattice under an electric field of about 10 kVcm⁻¹, from 9 K up to 80 K; the ratio of the intensities of the −1 and 0 peaks of the Wannier-Stark ladder varies with the temperature T. To fit these variations, we assume for both transitions, a trapped exciton density of states with a gaussian distribution of eigenenergies, and a two dimensional density of states for free excitons. We show that above about 50 K there is a thermal equilibrium between direct and crossed free excitons whereas at low temperatures, the equilibrium statistics are not respected: the excitons trap into the direct state rather than to the crossed one.     

Donor impurity states in direct-gap SiGe quantum well: Applied electric field and quantum size effects

Within the framework of the effective-mass approximation and variational procedure, competition effects between applied electric field and quantum size on donor impurity states in the direct-gap Ge/SiGe quantum well (QW) have been investigated theoretically. Numerical results show that the applied electric field (quantum size) dominates electron and impurity states in direct-gap Ge/SiGe QW with large (small) well width. Moreover, the competition effects also induce that the donor binding energies show obviously different behaviors with respect to electric field in the QW with different well widths. In particular, when the impurity is located at left boundary of the QW, the donor binding energy is insensitive to the variation of well width when well width is large for any electric field case.     

外电场对直接带隙Ge量子阱中的光学性质的影响

在有效质量近似下,考虑到外电场的影响,详细研究了直接带隙Ge/GeSi量子阱中带间光跃迁吸收系数和阈值能量随量子阱阱宽,外电场强度的变化情况。结果表明：随着外电场的增强,带间光跃迁吸收强度会逐渐减弱,阈值能量减小,吸收曲线向低能方向移动,出现了红移现象。此外,当量子阱比较大时,外电场对量子阱中带间光跃迁阈值能量的影响更加明显。     

Effective mass mismatch induced peculiarity in wavefunction behaviour in quantum well in electric field

The influence of the effective mass mismatch on wavefunctions in a quantum well in electric field is analysed. We found that for energies far from the well resonant states, the wavefunctions are highly influenced by the effective mass mismatch at well boundaries, while the well potential plays only a minor role, contrary to most other cases, where the reverse is true.     

Quenching of photoluminescence from GaAs/AlGaAs single quantum well by an electric field at high temperature

Photoluminescence measurements at room temperature and at liquid nitrogen temperature on a GaAs/AlGaAs single quantum well structure subject to an electric field are performed to study (i) the photoluminescence quenching and (ii) the shift in the photoluminescence energy induced by the field. The observed shifts in the luminescence energies are explained successfully in terms of the field induced electron-hole separation model. For the quenching of the luminescence intensities, more work, particularly on nonradiative processes, is required to clarify the mechanism.     

Electronic spectrum and wave functions in a double quantum well in a nonharmonic field

A method is proposed for calculating quasi-energies and quasi-energy wave functions of a particle located in a double quantum well under the action of a periodic external field with an arbitrary number of harmonics. The solutions of the Schrödinger equation obtained by this method are valid both in weak and strong fields for any frequencies of the external field and any frequencies of the quantum transition in the system.     

Excitonic Rabi oscillations in a quantum dot: local field impact

The influence of local fields on the excitonic Rabi oscillations in an isolated, arbitrary shaped quantum dot (QD) has been theoretically investigated. QD interaction with both a classical electromagnetic field and quantum light has been considered. In the classical light, time harmonic and ultrashort pulse excitations are analyzed. The general formalism has been formulated for quantum light and applied to the case of a Fock qubit. Noticeable modification of the Rabi oscillation dynamics induced by the local fields is predicted to be observable in QDs exposed to both classical and quantum light. In particular, the bifurcation and anharmonism in the Rabi oscillations have been revealed under time harmonic excitation and a dependence of the Rabi oscillation period on the QD depolarization has been obtained.     

Effects of laser field and electric field on impurity states in zinc-blende GaN/AlGaN quantum well

Based on the effective-mass approximation, the competition effects between the laser field and applied electric field on impurity states have been investigated variationally in the ZB GaN/AlGaN quantum well (QW). Numerical results show that for any laser field, the electric field makes the donor binding energy present asymmetric distribution with respect to the center of the QW. Moreover, when the laser field is weak, the electric field effects are obvious on the donor binding energy; however, the electric field effects are insensitive to the variation of donor binding energy in the ZB GaN/AlGaN QW with strong laser field.