Binding Energy Of Heavy-hole Exciton Research Articles

Effects of strain and hydrostatic pressure on exciton properties in asymmetric zinc-blende (In,Ga)N/GaN coupled double quantum wells

Within the effective mass approximation, we studied the light-hole and heavy-hole exciton states and their optical properties, such as oscillator strength and radiative decay time, in asymmetric zinc-blende GaN/InxGa1−xN/GaN/InyGa1−yN/GaN coupled double quantum wells. The variational method was performed under strain and hydrostatic pressure. The light-hole and heavy-hole exciton binding energies as a function of the left-well width and/or right-well width, middle-barrier thickness, and indium concentration x(y) of (In,Ga)N material are analyzed in detail. The light-hole and heavy-hole exciton binding energies show an increasing trend with increase of hydrostatic pressure. The hydrostatic pressure not only results in an increase in exciton binding energy, interband transition energy, and oscillator strength but also a decrease in the emission wavelength and radiative decay time. In addition, the biaxial strain dependence of the emission wavelength, radiative decay time, and interband transition energy of the exciton is very remarkable.

Exciton binding energies in CdSe/MgSe quantum well structures

Binding energies of heavy- and light-hole excitons in CdSe/MgSe quantum wells have been determined in terms of quantum well width. Hydrogenic wave functions are assumed to represent exciton wave functions. Contribution of the polarization charges originating from the dielectric mismatch between the well and the barrier materials to the Coulomb interaction is calculated by means of image charge method. The effect of the exciton-phonon interaction on the exciton binding energies are included by means of an effective potential obtained through an exciton-bulk-optical-phonon Hamiltonian. The results indicate that both the modified Coulomb interaction due to the dielectric mismatch and the exciton-phonon interaction considerably change the exciton binding energy. The heavy-hole exciton binding energy in a 10-Å quantum well is seen to be enhanced as much as 87% compared to the value found when only the Coulomb interaction without dielectric mismatch is taken into account. The resulting binding energies of heavy-hole excitons range approximately between 57 and 41 meV for the quantum well width changing between 10 and 35 Å. Compared to the bulk CdSe exciton binding energy 15 meV, the exciton binding energies in CdSe/MgSe quantum wells are increased almost four times.

Fractal dimension method for exciton in cylindrical GaAs/AlxGa1−xAs core-shell-cap nanowires

By use of the fractal dimension method, the binding energies of heavy-hole exciton and light-hole exciton in cylindrical GaAs/Al[Formula: see text]Ga[Formula: see text]As core-shell-cap nanowire are explored. In this study, the exciton is confined in GaAs shell of the GaAs/Al[Formula: see text]Ga[Formula: see text]As core-shell-cap nanowire for a given aluminum concentration of [Formula: see text][Formula: see text]=[Formula: see text]0.3. The numerical results of heavy-hole exciton binding energy, light-hole exciton binding energy and fractal dimension parameter are worked out as functions of shell width and core radius. It has been shown by the calculated results that heavy-hole exciton binding energy and light-hole exciton binding energy firstly increase and then decrease as the shell width increases. When the core radius increases, both the heavy-hole exciton binding energy and light-hole exciton binding energy increase gradually. Exciton problems in GaAs shell of the cylindrical GaAs/Al[Formula: see text]Ga[Formula: see text]As core-shell-cap nanowire are solved in a simple manner to avoid complex and lengthy calculations by using the fractal dimension method.

Dependence of heavy hole exciton binding energy and the strain distribution in GaAs1−xBix/GaAs finite spherical quantum dots on Bi content in the material

The ground state binding energy of heavy hole excitons confined in GaAs1−xBix/GaAs spherical quantum dots is calculated as a function of dot radius and the Bi content using a Variational method based on 1-s hydrogenic wave functions with effective mass approximation. The parameter shows strong dependence on the Bi mole fraction x, particularly at smaller values of the dot radii. The strain associated with the quantum dot is found to decrease exponentially with increase in dot radius and shows a linear increase with Bi composition.

Dielectric confinement on exciton binding energy and nonlinear optical properties in a strained Zn1−xinMgxinSe/Zn1−xoutMgxoutSe quantum well

The band offsets for a Zn1−xinMgxinSe/Zn1−xoutMgxoutSe quantum well heterostructure are determined using the model solid theory. The heavy hole exciton binding energies are investigated with various Mg alloy contents. The effect of mismatch between the dielectric constants between the well and the barrier is taken into account. The dependence of the excitonic transition energies on the geometrical confinement and the Mg alloy is discussed. Non-linear optical properties are determined using the compact density matrix approach. The linear, third order non-linear optical absorption coefficient values and the refractive index changes of the exciton are calculated for different concentrations of magnesium. The results show that the occurred blue shifts of the resonant peak due to the Mg incorporation give the information about the variation of two energy levels in the quantum well width.

Temperature and hydrostatic pressure effects on the binding energy of magnetoexcitons bound to ionized-donor impurities in GaAs/AlxGa1−xAs quantum wells

We have studied the quantum confinement, applied hydrostatic pressure, and temperature dependence of the binding energy of a magnetoexciton bound to a ionized-donor impurity in GaAs/Ga1-xAlxAs quantum wells, taking into account the spin-orbit coupling between the (Γ7v,Γ8v) and (Γ7c,Γ8c) multiplets, including the Al concentration, temperature, and applied hydrostatic pressure dependence on the electron effective-mass me(P,T,x) and the Landé ge(P,T,x) factor by using the well known five-level k · p theory. We have found that the binding energy Eb increases with the strong geometrical confinement, as well as with the growth-direction applied magnetic field. The presence of the ionized-donor impurity clearly increases the heavy-hole exciton binding energy. The quantum confinement, in part determined by the height of the barrier potential-well, i.e., by the Al concentration and the hydrostatic pressure, contributes to enhance the binding energy. Also, we found that the exciton binding energy increases with temperature due to the different temperature band-gap dependence of the well and barrier regions, which conduces to a net increasing of the potential barrier. Also, we have obtained a good agreement with previous theoretical and experimental findings. We hope the present work must be taken into account for the understanding of experimental reports and for the design of optoelectronic devices with multiple technological purposes.

Exciton Binding Energies in ZnSSe/MgSSe Quantum Wells Lattice Matched to GaAs Substrates

Exciton binding energies in ZnSSe/MgSSe single quantum wells (SQWs) are calculated to study their exciton properties in detail. The heavy-hole exciton binding energies are larger than the light-hole exciton binding energies in narrow wells because the degree of confinement of the heavy-hole excitons is larger than that of the light-hole excitons in these SQWs. The heavy-hole exciton binding and heavy-hole excitonic transition energies calculated for ZnSSe/MgSSe SQWs are comparable to those measured for ZnSe/MgS quantum wells. [DOI: 10.1380/ejssnt.2011.219]

Laser effects in excitons in a quantum wire

AbstractWe investigate the effects of laser field intensity over the ground state binding energy of light and heavy hole excitons confined in GaAs/Ga1−xAlx As cylindrical quantum wire. We have applied the variational method using 1s‐hydrogenic wave functions, in the framework of the single band effective mass approximation with the spatial dielectric function. The polaronic effects are included in the calculation to compute the exciton binding energy as a function of the wire radius for different field of laser intensity. The valence‐band anisotropy is included in our theoretical model by using different hole masses in different spatial directions. The dressed laser donor binding energies are calculated and compared with the results of binding energy of excitons. The results show that (i) the binding energy is found to increase with decrease with the wire radius, and decrease with increase with the value of laser field amplitude, (ii) the heavy‐hole exciton in a cylindrical quantum wire is more strongly bound than the light‐hole exciton, (iii) the values of ground state binding energy for the laser field amplitude α0 = 10 Å resemble with the values of heavy hole exciton binding energy, and (iv) the binding energy of the impurity for the narrow well wire is more sensitive to the laser field amplitude. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2011

Effect of Exciton-Longitudinal Optical Phonon Interaction on Exciton Binding Energies in CdxZn1-xS/ZnS Single Quantum Wells

We study the effect of the exciton-longitudinal optical (LO) phonon interaction on the exciton binding energies in CdxZn1-xS/ZnS single quantum wells (SQWs) for the Cd alloy content (x) range 0.1—0.3. The heavy- and light-hole exciton binding energies increase with the exciton-LO phonon interaction. The increase in the maximum heavy-hole (light-hole) exciton binding energy for x = 0.3 is 9.1 meV (4.9 meV). In narrow CdxZn1-xS/ZnS SQWs, the heavy-hole exciton binding energy calculated by taking into account the exciton-LO phonon interaction for values of x in the range 0.1—0.3 exceed the LO phonon energy of CdxZn1-xS. [DOI: 10.1380/ejssnt.2010.340]

Exciton Binding Energies in Cd0.11Zn0.89S/Mg0.22Zn0.78S Quantum Wells Lattice-Matched to GaP Substrates

The exciton binding energy in Cd0.11Zn0.89S/Mg0.22Zn0.78S single quantum wells (SQWs) is calculated to study their exciton properties in detail. The heavy-hole exciton binding energy is larger than the light-hole exciton binding energy in narrow wells, because the degree of confinement of heavy-hole excitons is larger than that of light-hole excitons in these SQWs. The heavy- and light-hole exciton binding energies are found to increase owing to the image-charge effect when the well width is less than 5 nm.

Binding energies of excitons in a strained wurtzite GaN/AlGaN quantum well influenced byscreening and hydrostatic pressure

In the framework of effective mass and single-band approximations, avariational method combined with a self-consistent procedure is adopted todiscuss the binding energies of heavy-hole excitons in a strained wurtziteGaN/Al0.3Ga0.7N quantum well by considering the hydrostatic pressure effect and screeningdue to the electron–hole gas. The built-in electric field in such a structureproduced by spontaneous polarization and strain-induced piezoelectricpolarization is considered in our calculation. A simplified coherent potentialapproximation is extended to calculate the energy gaps of the ternary mixed crystalAlxGa1−xN. The result indicates that the binding energies of excitons increase nearly linearly withpressure even when taking into consideration the modification of strain. It is also foundthat the percentage increase of the binding energy with pressure is influenced by theelectron–hole density due to the influence of pressure on the screening and exclusion effects.The excitonic binding energies increase obviously with decreasing barrier thickness due tothe built-in electric field.

Photoluminescence of heavily doped GaAs/AlGaAs quantum wells in high magnetic fields

We studied the photoluminescence in GaAs/AlGaAs single quantum wells at fields up to a maximum of 22 T and observed spectra due to impurities, heavy-hole excitons, and Landau levels. The wells were doped with Si at different doping levels up to 3 × 10 18 cm −3 in order to examine this influence on the photoluminescence. We compare results from two well widths, 50 Å and 100 Å, over an energy range from about 1.4 to 1.7 eV. From the dependence on field of the Landau levels, a cyclotron mass ratio of 0.11 ± 0.02 was determined, which is larger than the bulk GaAs mass ratio of 0.067. The heavy-hole exciton binding energy was about 15 meV for the 100 Å well.

Effects of electron-phonon interaction on exciton binding energy in a quantum well

Using Lee-Low-Pines transformation and perturbative variational method, the effects of electron-phonon interaction on the exciton binding energy in a Ga 1− x Al x As quantum well can be solved analytically. Our results show that the phonon effect on binding energy of heavy-hole exciton is always larger than that of light-hole exciton and the correction of polaron effect on the exciton binding energy in a quantum well cannot be neglected.

Excitonic properties of Zn1-xCdxSe/ZnSe strained quantum wells.

We present a systematic investigation of the linear optical properties of ${\mathrm{Zn}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Cd}}_{\mathit{x}}$Se/AnSe multiple quantum well structures in the excitonic region using absorption and photoluminescence measurements in the 10--300 K temperature range. Heavy- and light-hole excitonic transitions and heavy-hole exciton binding energies were measured for different well widths and compositions. A set of consistent parameters was determined within a two-band model, which accurately describes the excitonic properties of the strained ${\mathrm{Zn}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Cd}}_{\mathit{x}}$Se quantum wells.

Quantum wells with corrugated interfaces: Theory of electron states.

We present realistic effective-mass calculations of electron and exciton states in [311] GaAs/AlAs corrugated quantum wells (QW's) taking into consideration a finite barrier potential and flux-conserving boundary conditions. One-dimensional minibands are formed in the periodic lateral corrugation potential. Light- and heavy-hole exciton binding energies are calculated as a function of QW effective width and discussed in connection with existing experimental data.

Comparison of 1s-2s exciton-energy splittings between (001) and (111) GaAs/AlxGa1-xAs quantum wells.

We have observed 2s excitonic emission from (111)-oriented GaAs/${\mathrm{Al}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$As quantum wells. This observation enables us to make an accurate comparison of the 1s-2s exciton-energy splittings in the photoluminescence spectra of (111) quantum wells with those of (001) quantum wells. It is found that the binding energies of heavy-hole excitons are smaller in (111) quantum wells than in (001) quantum wells with the same well widths. This result is qualitatively consistent with theoretical predictions based on an effective-mass approximation.

Well-width and aluminum-concentration dependence of the exciton binding energies in GaAs/AlxGa1-xAs quantum wells.

A photoluminescence-excitation (PLE) study of the exciton binding energy in GaAs/${\mathrm{Al}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$As quantum-well (QW) structures is reported. A line-shape fit of the PLE spectra, based on a correct evaluation of the absorption probability in QW's, is proposed as a powerful tool in order to deduce accurately the exciton binding energies even in samples where the 2s peak is unresolved. The experimental results obtained are in good agreement with recent accurate theories. In particular, we find a strong dependence of the heavy-hole exciton binding energy ${\mathit{E}}_{1}$ on the aluminum concentration of the ${\mathrm{Al}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$As barrier, in agreement with the predicted importance of the dielectric mismatch and conduction-band nonparabolicity in enhancing ${\mathit{E}}_{1}$. Finally, evidence of exciton binding energies larger than the two-dimensional limit in GaAs is found even in relatively thick QW's (50 \AA{}) with AlAs barriers.

Exciton binding energies in CdTe/Cd 1−xMn xTe multiple quantum wells

These results are compared with binding energies calculated with a variational approach which accounts for motion along the z-direction as well as in the x-y plane. The 1S and 2S states of both light hole, (e 1, ℓ 1), and heavy hole (e 1h 1) excitons have been observed in CdTe/Cd 1−xMn xTe multiple quantum wells. Clear identification of the 2S states arises from their large diamagnetic effects and their observation has allowed the light and heavy hole exciton binding energies to be investigated with changes in depth of the electron and hole confining potentials by application of a magnetic field. In a sample with x ∼ 0.75 it is found that changes of the heavy hole exciton binding energies are small, ⪅ 1 2 meV, even for large changes, ≈40 meV, of the hole confining potential. For the light hole exciton changes of the binding energy are larger, ≅ 2meV, for smaller changes, ≅ 14meV, of the hole confining potential.

Magnetoexcitons in narrow GaAs/Ga1-xAlxAs quantum wells.

We present results of our magneto-optical studies of excitonic transitions in narrow GaAs quantum wells, i.e., in the case when the heavy-hole--light-hole splitting is significantly larger than the heavy-hole exciton binding energy. The main (s-type) heavy-hole transitions can be simply understood in terms of two-dimensional hydrogeniclike magnetic levels. A giant repulsion occurring between the 3${\mathit{d}}^{\mathrm{\ensuremath{-}}}$ heavy-hole and the 1s light-hole states demonstrates the importance of Coulomb interaction in the mixing of magnetoexcitonic levels.

(InGa)AsGaAs strained layer quantum wells — excitonic properties and electronic structure

The heavy-hole exciton binding energy in 14 and 25 Å In 0.15Ga 0.85AsGaAs isolated quantum wells has been measured directly. We report the first direct observation of a decrease in binding energy with decreasing well width. Favourable comparisons with our calculation of this quantity are presented.