Impurity In Quantum Research Articles

Inter-sub-band transitions and binding energies of donor impurities in a modulation-doped quantum well in the presence of electric field

In this study, we have investigated theoretically the effects of the electric field and doping concentration on the optical transitions in a modulation-doped GaAs-AlGaAs quantum well for different well widths. The binding energies of the donor have also been computed using a trial wave function with two parameters in the framework of an effective-mass approximation. The electronic structure of a modulation-doped quantum well under the electric field is determined by solving the Schrödinger and Poisson equations self-consistently in the effective-mass approximation. The results obtained show that inter-sub-band transitions and the energy levels in the modulation-doped quantum well can be significantly modified and controlled by the well width and donor concentration. The sensitivity to the well widths of the absorption coefficient can be used in various optical semiconductor devices’ applications.

The electronic properties of a coaxial square GaAs/Al xGa 1−xAs quantum well wire in an electric field

The binding energy of a hydrogenic impurity in a coaxial square quantum well wire (QWW) system is investigated as a function of the barrier thickness for two different impurity positions under the electric fields. Within the effective mass approximation, the ground state energy in the presence of an external electric field applied perpendicular to the symmetry axis of the wire system is calculated using the finite difference method. Then, the ground state binding energy of a hydrogenic impurity is found employing a variational method. It is found that the binding energy in critical barrier thickness shows an increase or decrease depending on the impurity position and electric field strength.

Binding energy of donor impurities in double inverse parabolic quantum well under electric field

In this study, effects of the electric field applied along the growth direction on the binding energy of donor impurities in double inverse parabolic quantum well (DIPQW) with different well and barrier widths, as well as different Al concentrations in the center of the wells have been investigated. The Al concentration at the barriers was always x max=0.3. The calculations were performed within the effective mass approximation, using a variational method.

The effect of the last quantum barrier on the internal quantum efficiency of InGaN-light emitting diode

The effect of the last quantum barrier (LQB) on the internal quantum efficiency of GaN-light emitting diode (LED) was systematically investigated using a dual-wavelength GaN-LED design. Compared with a conventional GaN-LQB, a high indium contained In0.03Ga0.97N-LQB efficiently reduced the unintentional Mg impurity in the last quantum well and improved its photoluminescence and electroluminescence intensity up to 72% and 15%, respectively.

Electric and magnetic field effects on the binding energy of a hydrogenic impurity in quantum well wires with different shapes

In this work, we directly calculate the ground state energies for an electron in quantum well wires (QWWs) with different shapes in the presence of applied electric and magnetic fields using the finite difference method. Then, we study the ground state binding energy of a hydrogenic impurity with a variational approach. We obtain the binding energy for QWWs consisting of the combinations of square and parabolic well potential. Our results indicate that the impurity binding energy depends strongly on the structural confinement and also, on the applied electric and magnetic field.

Magneto-absorption of donor impurities in quantum-well wires

We show calculations for far-infrared absorption of shallow-donor impurities in quantum well wires in the presence of an external magnetic field. The wave functions and the eigenvalues are obtained in the effective-mass approximation by using an extended variational approach in which the ground and excited magneto-impurity states are simultaneously obtained. We investigate the allowed intra-donor transitions for radiation circularly polarized in the plane perpendicular to the magnetic field. We present results for the absorption coefficient as a function of the photon energy for several field strengths and arbitrary impurity positions.

Binding Energy of Hydrogen-Like Impurities in Quantum Well Wires of InSb/GaAs in a Magnetic Field

The binding energy of a hydrogen-like impurity in a thin size-quantized wire of the InSb/GaAs semiconductors with Kane’s dispersion law in a magnetic fieldBparallel to the wire axis has been calculated as a function of the radius of the wire and magnitude ofB, using a variational approach. It is shown that when wire radius is less than the Bohr radius of the impurity, the nonparabolicity of dispersion law of charge carriers leads to a considerable increase of the binding energy in the magnetic field, as well as to a more rapid growth of binding energy with growth ofB.

Binding Energy of an Off-Center Hydrogenic Donor Impurity in a Finite Confining Potential Quantum Well

Low dimensional semiconductor heterostructures such as quantum wells, wires, boxes, and dots have gained a great importance in the last two decades due to their fundamental properties and their wide range of applications. Special care has been given to investigate these quantum systems in the presence of shallow impurities [1{9]. The problem of calculating the binding energy of hydrogenic impurity in a quantum well has been considered in the pioneering work of Bastard [10]. He studied the case of center and ofi-center impurity but in an inflnite conflning potential quantum well. He applied a variational approach that was based on modifying the exact wave function of an inflnite quantum well by adding a term that represents the hydrogenic impurity. The resulting trial wave function depends on one variational parameter. The case of flnite conflning potential quantum well was dealt with by using a similar approach by Chaudhuri and Bajaj [11] and Elabsy [12]. Jia-Lin Zhu [13] and Greene and Bajaj [14, 15] applied more complicated variational methods. However, in all these treatments the case of a

The polarizability and the photoionization cross‐section under the external fields for donor impurities in quantum well‐wire

AbstractIn this study, we have calculated the donor impurity binding energy, donor impurity related photoionization cross‐section and polarizability in symmetric GaAs/Ga1–x Alx As quantum well‐wire as a function of the impurity positions, dimensions of the structures and external electric and magnetic field, the calculations were performed within the effective mass approximation, using a variational method. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Barrier height effect on binding energies of shallow hydrogenic impurities in coaxial GaAs/ AlxGa1−xAs quantum well wires under a uniform magnetic field

Abstract The ground state binding energies of axial hydrogenic impurities in a coaxial cylindrical quantum well wire are reported as a function of the barrier height and the radius of wire in the presence of a uniform magnetic field applied parallel to the wire axis. The quantum well wire (QWW) is assumed to be an infinitely long cylinder of GaAs material surrounded by AlxGa1−xAs (for finite case and vacuum for infinite case). Binding energy calculations were performed with the use of a variational procedure in the effective mass approximation. We observed that the binding energy is sensitive to well radius only for both larger R values and small magnetic fields. We also compared the infinite and finite case binding energies and showed that increasing the Al concentration in the finite barrier case, binding energies are increased as expected. Our results are in good agreement and complementary with the previous theoretical works.

Density of impurity states of hydrogenic impurities in an inverse parabolic quantum well under the magnetic field

We investigated the effects of the magnetic field on the density of impurity states in a GaAs/GaAlAs inverse parabolic quantum well (IPQW) for different Al concentrations at the well center. The calculations were performed within the effective mass approximation, using a variational method. We report in this paper the effects of the magnetic field, well width and the Al concentration at the well center on the density of states and the binding energies of the donor impurities.

Binding energy of impurity states in an inverse parabolic quantum well under magnetic field

We have investigated the effects of the magnetic field which is directed perpendicular to the well on the binding energy of the hydrogenic impurities in an inverse parabolic quantum well (IPQW) with different widths as well as different Al concentrations at the well center. The Al concentration at the barriers was always x max = 0.3 . The calculations were performed within the effective mass approximation, using a variational method. We observe that IPQW structure turns into parabolic quantum well with the inversion effect of the magnetic field and donor impurity binding energy in IPQW strongly depends on the magnetic field, Al concentration at the well center and well dimensions.

Electric and magnetic field effects on the binding energy of a hydrogenic donor impurity in a coaxial quantum well wire

The effect of both an electric and magnetic field on the hydrogenic binding energy of a shallow donor impurity in a coaxial GaAs-(Ga, Al)As quantum well wire (QWW) has been investigated as a function of the impurity position and barrier thicknesses for different values of the applied magnetic and electric field strengths. Within the effective mass approximation, the ground-state energy in the presence of a uniform magnetic field applied parallel to the wire axis has been calculated using the fourth-order Runge–Kutta method. The ground state binding energy under applied electric field has been studied with a variational approach. The two sharp increase in the binding energy have observed for the donor impurity located at outside of the center under the critical electric and magnetic field values. However, for the electric field off the binding energy monotonously decrease with increasing magnetic field strength up to a critical magnetic field and then a sharp decrease is seen before reaching a constant value. For the impurity located at the center, the abrupt deviations of the binding energy strongly depend not only on the electronic confinement, but also on the electric and magnetic field strength. We expect that these results will be useful in technological applications.

Shallow donor impurities in different shaped double quantum wells under the hydrostatic pressure and applied electric field

The combined electric field and hydrostatic pressure effects on the binding energy of the donor impurity in double triangle quantum well (DTQW), double graded (DGQW) and double square (DSQW) GaAs–(Ga,Al)As quantum wells are calculated by using a variational technique within the effective-mass approximation. The results have been obtained in the presence of an electric field applied along the growth direction as a function of hydrostatic pressure, the impurity position, barrier width and the geometric shape of the double quantum wells.

Resonant impurity and exciton states in a narrow quantum well

An analytical investigation of resonant impurity and exciton states in a narrow quantum well (QW) is performed. We employ the adiabatic multisubband approximation assuming that the motions parallel and perpendicular to the heteroplanes separate adiabatically. The coupling between the Coulomb states associated with the different size-quantized subbands ($N=1$, 2, \dots{}) is taken into account. In the two- and three-subband approximation the spectrum of the complex energies of the impurity electron and the exciton optical absorption coefficient are derived in an explicit form. The spectrum comprises a sequence of series of quasi-Coulomb levels $(n)$ where only the series belonging to the ground subband $N=1$ is truly discrete while the excited series $N\ensuremath{\geqslant}2$ consist of quasi-discrete energy levels possessing non-zero widths ${\ensuremath{\Gamma}}_{Nn}$. Narrowing the QW leads to an increase of the binding energy and to a decrease of the resonant energy width ${\ensuremath{\Gamma}}_{Nn}$ and the resonant energy shift $\ensuremath{\Delta}{E}_{Nn}$ of the impurity electron. Displacing the impurity center from the midpoint of the QW causes the binding energy to decrease while the width ${\ensuremath{\Gamma}}_{Nn}$ and the corresponding shift $\ensuremath{\Delta}{E}_{Nn}$ both increase. A Lorentzian form is recovered for the exciton absorption profile. The absorption peak is narrowed and blue shifted for a narrowing of the quantum well. A successful comparison with existing numerical data is performed. For GaAs QW's it is shown that the resonant states analyzed here are sufficiently stable to be observed experimentally.

Shallow donor impurity binding energy in the V-shaped quantum well under the crossed electric and magnetic fields

We have calculated variationally the ground state binding energy of a hydrogenic donor impurity in V-shaped quantum well (VQW) or full-graded GaAs / Ga 1 - x Al x As quantum wells in the presence of crossed electric and magnetic fields. These homogeneous crossed fields are such that the magnetic field is parallel to the heterostructure layers and the electric field is applied perpendicular to the magnetic field. The dependence of the donor impurity binding energy on the well width and the strength of the electric and magnetic fields are discussed. We hope that obtained results will provide important improvements in device applications, especially for narrow well widths and for a suitable choice of both fields.

Effects of Crossed Electric and Magnetic Fields on ShallowDonor Impurity Binding Energy in a Parabolic Quantum Well

We have calculated variationally the ground state binding energy of ahydrogenic donor impurity in a parabolic quantum well in the presenceof crossed electric and magnetic fields. These homogeneous crossedfields are such that the magnetic field is parallel to theheterostructure layers and the electric field is applied perpendicularto the magnetic field. The dependence of the donor impurity bindingenergy to the well width and the strength of the electric and magneticfields are discussed. We hope that the obtained results will provideimportant improvements in device applications, especially for asuitable choice of both fields in the narrow well widths.

Binding energy of relativistic hydrogenic impurities in cylindrical quantum well wires under an applied electric field

AbstractThe ground state binding energy of a hydrogenic impurity in infinite cylindrical GaAs quantum well wires subjected to an external electric field applied perpendicular to the symmetry axis of the wire is studied within the relativistic approach. A rapid decrease of the binding energy for different intensities of the electric field with increasing wire radius is predicted. Furthermore, the relativistic effects are emphasised by comparing them with the non‐relativistic results. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Shallow donor impurities in different shaped double quantum wells under the electric field

AbstractThe binding energy of the donor impurity in double triangle quantum well (DTQW), double graded (DGQW) and double square (DSQW) GaAs–(Ga,Al)As quantum wells under the electric field is calculated by using a variational approach. The results have been obtained in the presence electric field applied along the growth direction as a function of the impurity position, barrier width and the geometric shape of the double quantum wells. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Giant quantum oscillations of nuclear spin relaxation rate in QHE systems with magnetic impurities

We study the phonon-assisted mechanism for nuclear spin relaxation (NSR) of magnetic impurity in two-dimensional electron gas system under quantum-Hall effect conditions. The nuclear spin impurity interacts mainly with discrete bound Landau state caused by resonance scattering with the impurity. The lattice distortion around the defect creates localized phonons which take part in the spin-flip transition. It is found that in the field dependence of the NSR rate T 1 −1 only the equidistant resonance transitions depending on the frequency of the localized phonon are allowed. This spectral structure may be used as a probe for studying the localized vibrational modes frequency and the electron–phonon coupling for various magnetic impurities. The obtained NSR rate, T 1 −1, oscillates periodically in the inverse magnetic field. Estimation for Fe impurity in GaAs quantum well is given.