The effect of nonparabolicity on binding energy of ground and excited states in a corrugated quantum well

The binding energy of a hydrogenic impurity is calculated in a Ga_1−xAl_xAs/Ga_1−yAl_yAs corrugated quantum well within the single band effective mass approximation for different Al concentration. Binding energy of the ground state and the excited state of a donor is calculated, with the inclusion of 2D Hartree dielectric screening function. The effect of nonparabolicity of the conduction band is considered through the energy dependent effective mass. The effect of nonparabolicity on spin–orbit interaction energy is found. The oscillator strength coupling between the ground state and the excited state is calculated. The dependence of the donor binding energy on the well width and the Al-concentration is discussed. These results are discussed with the available data in the literature.     

Electromodulation spectroscopy of In0.53Ga0.47As/In0.53Ga0.23Al0.24As quantum wells

In_0.53Ga_0.47As/In_0.53Ga_0.23Al_0.24As quantum wells (QWs) of various widths have been grown by molecular beam epitaxy on the InP substrate and investigated by electromodulation spectroscopy, i.e. photoreflectance (PR) and contactless electroreflectance (CER). The optical transitions related to the QW barrier and the QW ground and excited states have been clearly observed in PR and CER spectra. The experimental QW transition energies have been compared with theoretical predictions based on an effective mass formalism model. A good agreement between experimental data and theoretical calculations has been observed when the conduction band offset for the In_0.53Ga_0.47As/In_0.53Ga_0.23Al_0.24As interface equals 60%. In addition, it has been concluded that the conduction band offset for the In_0.53Ga_0.23Al_0.24As/InP interface is close to zero. The obtained results show that InGa(Al)As alloys are very promising materials in the band gap engineering for structures grown on InP substrate.     

Effect of laser intensity on the semiconductor–metal transition in a doped Quantum Well

We demonstrate laser induced semiconductor–metal transition through an abrupt change in diamagnetic susceptibility of a donor at critical concentration in a GaAs/Al_xGa_1−xAs Quantum Well for finite barrier model in the effective mass approximation using variational principle. We have considered Anderson‘s localization due to the random distribution of impurities in our calculation. The nonparabolicity of the conduction band is also considered. Our results without laser field agree with the earlier theoretical results and also with the recent experimental results.     

Diamagnetic susceptibility of hydrogenic donor impurity in low-dimensional semiconducting systems

The binding energies of a hydrogenic donor both in the parabolic and non-parabolic conduction band model within the effective mass approximation have been computed for the low-dimensional semiconducting systems (LDSS) like quantum well, quantum well wire and quantum dot taking GaAs/Al_xGa_1−xAs systems as an example. It is observed that the effect of non-parabolicity is not effective when the system goes to lower dimensionality. The diamagnetic susceptibility of a hydrogenic donor impurity has also been computed in these LDSS in the infinite barrier model. Since no theoretical or experimental works on the diamagnetic susceptibility of LDSS are available in the literature, as a realistic case the diamagnetic susceptibility has been computed in the finite barrier model (x=0.3) for a quantum well and the results are discussed in the light of semiconductor-metal transition.     

Donor impurity states in coupled quantum well wires under hydrostatic pressure and applied electric field

In this work we study the binding energy of the ground state for a hydrogenic donor impurity in laterally coupled GaAs/Ga_1−xAl_xAs quantum well wires, considering the simultaneous effects of hydrostatic pressure and applied electric field. We have used a variational method and the effective mass and parabolic band approximations. The low dimensional structure consists of two quantum well wires with rectangular transverse section coupled by a central Ga_1−xAl_xAs barrier. Our results are reported for several sizes of the structure and we have taken into account variations of the impurity position along the growth direction of the heterostructure.     

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.     

Electronic structures of GaAs/AlGaAs concentric double rings in applied electric and magnetic field

The electronic structures of GaAs/Al_0.35Ga_0.65As concentric double rings are calculated based on the effective mass envelope function theory, with and without the applied electric and magnetic field along the growth direction. The Hamiltonian matrix elements are determined through the Fourier transform method. As the heterostructure evolves from a single ring to the concentric double rings, our simulation is performed on the bound state energies of the electron and the hole. The results show that the energy levels undulate with the evolution of the ring. The applied magnetic field increases the ground state energies both of the electron and of the hole, as well as the transition energy between the first conduction subband and valence subband. However, the electric field decreases the electronic energies linearly.     

External electric field, hydrostatic pressure and conduction band non-parabolicity effects on the binding energy and the diamagnetic susceptibility of a hydrogenic impurity quantum dot

Electric field, hydrostatic pressure and conduction band non-parabolicity effects on the binding energies of the lower-lying states and the diamagnetic susceptibility of an on-center hydrogenic impurity confined in a typical GaAs/Al_xGa_1−xAs spherical quantum dot is theoretically investigated, by direct diagonalization of the Hamiltonian. To this end, the effect of band non-parabolicity has been performed, by means of the Luttinger-Kohn effective mass equation. Binding energies and diamagnetic susceptibility of the hydrogenic impurity are computed as a function of the dot size, external electric field strength and hydrostatic pressure, with considering the edge-band non-parabolicity. Results show that the external electric field and the hydrostatic pressure have an obvious influence on the binding energies and the diamagnetic susceptibility of the impurity.     

Time-resolved polarized photoluminescence spectroscopy of confined donors in GaAs/AlxGa1-xAs quantum wells

We report on the recombination dynamics of band edge photoluminescence (PL) in GaAs/Al_xGa_1-xAs multiple quantum wells which have been selectively doped with Si donors at a variety of positions across the well. We observe PL lines associated with the ground state n = 1 light and heavy hole exciton transitions, as well as several bound exciton states and a donor-to-continuum transition which occur below the dominant heavy hole excitons. The recombination lifetime of the donor-to-continuum (Si(c)→VB) transition is significantly longer than that measured for the excitonic transitions. The Si(c)→VB transition is 20 times longer than the lifetime of the hhX. This result clearly suggests that this line is not an exciton-related transition and may be consistent with what is expected for a localized donor-to-continuum transition. Measurements of the lifetime as a function of temperature and a measure of the recombination dynamics as a function of magnetic field support this conclusion.     

Energy levels in rectangular quantum well wires based on a modified profile of the heterojunction

The effect of a spatially dependent effective mass on the energy levels in a rectangular quantum wire with finite barrier potential is considered. The heterojunction is modelled by an error function rather than a step function to more accurately model the material transition region at the interface between the two materials. The carrier ground state is calculated using the envelope function approximation for Ga_0.47In_0.53As/InP and GaAs/Ga_0.63Al_0.37As systems. The results are lower than those reported before, and are in better agreement with the experimental points.     

Polarizability of a hydrogenic donor impurity in a ridge quantum wire

We use in this paper the variational method to calculate the polarizability of a hydrogenic donor impurity, in the presence of electric field, in a V-groove GaAs/Al_xGa_1−xAs quantum wire. The carrier ground states are analytically obtained by an effective potential scheme together with a suitable coordinate transformation that allows the decoupling of the two-dimensional Schrodinger equation. According to the results obtained from the present work for polarizability and binding energy reveals that the impurity position and field direction play important roles.     

Excitonic spectrum of an undoped quantum well in electric field

The effect of the valence band coupling on the excitonic spectrum of an undoped GaAsAl_xGa_1−xAs quantum well subjected to a normal electric field is examined. The exciton states are split because of the spin-splitting of the hole subbands. The binding energies of the (00h) and (001) excitons are noticeably increased. The transition strength of the “forbidden” (01h) exciton is enhanced both by the electric field and the strong mixing of the hole states. The binding of the 001 exciton is further increased because it exhibits a Fano-like resonance with the electron-heavy hole continuum.     

Simultaneous effects of pressure and temperature on donors in a GaAlAs/GaAs quantum well

The ground state and a few excited state energies of a hydrogenic donor in a quantum well are computed in the presence of pressure and temperature. The binding energies are worked out for GaAs/ Ga_1−xAl_xAs structures as a function of well size when the pressure and temperature are applied simultaneously. A variational approach within the effective mass approximation is considered. The results show that for a constant applied pressure, an increase in temperature results in a decrease in donor impurity binding energy while an increase in the pressure for the same temperature enhances the binding energy. When the pressure and temperature are applied simultaneously the binding energy decreases as the well width increases. In all the cases, it is observed that there is an increase in the binding energy due to the decrease in the quantum well size and in the dielectric constant whereas the effects of temperature on the effective mass are minimal.     

Confined electron and shallow donor states in graded GaAs/Al Ga As spherical quantum dots

A theoretical study is performed on the confined electron and shallow donor states properties in graded GaAs/Al_xGa_1-xAs spherical quantum dots. The two lowest energy levels of a confined electron are obtained taking into account the dependence of the electron effective mass on the spatial profile of the Al molar fraction. The ground state of a single Si shallow donor, which may be located at an arbitrary position in the structure, is calculated through a variational approach. Depending on the dot interface width and localization, we find that the energy levels of the electron and donor states for the system under study can be blue or red shifted appreciably in comparison to those calculated within the sharp interface picture. We show that it is necessary to have accurate information concerning the interface of semiconductor dots whose samples are used in the experiments, in order to achieve a better understanding of their optical properties. Received 31 May 1999     

Diamagnetic susceptibility of hydrogenic donor impurity in a V-groove GaAs/Ga<Subscript>1-</Subscript><Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Al<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>As quantum wire

In this work, the diamagnetic susceptibility and the bindingenergy of a hydrogenic donor impurity both in the parabolic andnon-parabolic conduction band models have been calculated withinthe effective mass approximation for a V-grooveGaAs/Ga_{1- x} Al _x As quantum wire. According to the resultsobtained from the present work reveals that (i) the value ofdiamagnetic susceptibility due to the non-parabolicity effect ishigher than that of parabolicity effect; (ii) the values ofdiamagnetic susceptibility and binding energy due to thenon-parabolicity effect is not appreciable at low Al molefractions; (iii) the diamagnetic susceptibility approaches to thebulk value both in L \(\rightarrow\) 0 or L \(\rightarrow\) ∞; (iv)the effect of non-parabolocity is not appreciable in the bindingenergy and energy dependent effective mass, for energies lowerthan 50 MeV.     

Excited state resonant tunneling in GaAsAlxGa1−xAs double barrier heterostructures

Resonant tunneling through the ground and first excited state of single quantum well, double barrier GaAsAl_xGa_1−xAs heterostructures is reported. Negative differential resistance from both quantum well states is observable up to room temperature in one of these structures. The observed positions of the quantum well states agree well with theory, though there exists an asymmetry in the current-voltage characteristics about the origin.     

Effect of Γ-X band crossover and impurity location on the diamagnetic susceptibility of a donor in a quantum well

We present the calculation of diamagnetic susceptibility (χ_dia) of a hydrogenic donor in GaAs/Al_xGa_1−xAs quantum well for various compositions of Al and for different impurity locations within the well. The effect of Γ-X band crossing due to hydrostatic pressure on χ_dia is also investigated taking into account the non-parabolicity of the conduction band.     

Tuning a conventional quantum well laser by nonresonant laser field dressing of the active layer

Tunable semiconductor lasers may be considered as a critical technology for optical communications. We investigate the theoretical feasibility of tuning a conventional GaAs/Al_0.2Ga_0.8As quantum well laser emitting at 825 nm by non-resonant laser-dressing of the active layer. Conduction and valence subbands are sensitive to the intense dressing field and this effect can be used to blueshift the active interband transition. The laser-dressed electron and hole states are calculated in the effective mass approximation by using the finite difference method. Emitted wavelength, threshold current and characteristic temperature are discussed as functions of the dressing laser parameter and cavity length.     

Nonlinear optical properties of biexciton states in GaN quantum disks

The ground state energy of an exciton and biexciton states, in a GaN/Al_xGa_1-xN quantum disk are investigated by the variation method, within envelope function and effective mass approximations. Exciton and biexciton binding energy, and the dipole moments related to the transition between ground, exciton and biexciton states, are calculated as a function of quantum disk geometry. The optical nonlinearity via the exciton and biexciton states is studied on the basis of a three level model through the density matrix formalism. The behavior of different terms of third order susceptibility χ⁽³⁾, are studied around resonance frequencies and for different geometries of disk. The effect of values of the decay rates on χ⁽³⁾ are studied. It is found that these values have remarkable effect on the second term of, χ⁽³⁾.     

The high hydrostatic pressure effect on shallow donor binding energies in GaAs-(Ga, Al)As cylindrical quantum well wires at selected temperatures

We have presented the behavior of a shallow donor impurity with binding energy in cylindrical-shaped GaAs/Ga_0.7Al_0.3As quantum well wires under high hydrostatic pressure values. Our results are obtained in the effective mass approximation using the variational procedures. In our calculations, we have not considered the pressure related Γ−X crossover effects. The hydrostatic pressure dependence on the expectation value of ground state binding energy is calculated as a function of wire radius at selected temperatures. We have also discussed the effects of high hydrostatic pressure and temperature on some physical parameters such as effective mass, dielectric constant, and barrier height. A detailed analysis of these calculations has proved that the effective mass is the most important parameter, which explains the dependency of donor impurity binding energies on the high hydrostatic pressure values.