D. A. Contreras-Solorio

Electronic states in diffused quantum wells

In the present study we calculate the energy values and the spatial distributions of the bound electronic states in some diffused quantum wells. The calculations are performed within the virtual crystal approximation, sp3s* spin dependent empirical tight-binding model and the surface Green function matching method. A good agreement is found between our results and experimental data obtained for AlGaAs/GaAs quantum wells with thermally induced changes in the profile at the interfaces. Our calculations show that for diffusion lengths LD=0−20 A the optical transition between the ground electron and hole states is less sensitive to the LD changes than the optical transitions between the excited electron and hole states. For diffusion lengths LD=20−100 A, the optical transition between the second excited states is not sensitive to the diffusion length, but the other optical transitions display large “blue shifts” as LD increases. The observed dependence is explained in terms of the bound states spatial distrib...

The polaron in a GaAs/AlAs quantum well

Abstract Polaron binding energy and effective mass are calculated for the case of a GaAs/AlAs quantum well with the use of a phenomenological model for the long-wavelength polar optical oscillations which accounts for the coupling between the longitudinal and transverse components of the vibrations as well as for the coupling between mechanical and electrical fields. It is shown that the contribution of GaAs-like modes to the electron–phonon interaction in that system, gives polaronic corrections with values well below those obtained in previous works.

Magneto-optical effects in quantum wells irradiated with light pulses

The method of detection and investigation of the magnetopolaron effect in the semiconductor quantum wells (QW) in a strong magnetic field, based on pulse light irradiation and measuring the reflected and transmitted pulses, has been proposed. It has been shown that a beating amplitude on the frequencies, corresponding to the magnetopolaron energy level splitting, depends strongly on the exciting pulse width. The existence of the time points of the total reflection and total transparency has been predicted. The high orders of the perturbation theory on electron-electromagnetic field interaction have been taken into account. Time resolved scattering (TRS) investigations of the excitons in the semiconductor bulk crystals and QWs have been discussed in the current literature [1,2]. The most interesting results are due to the discrete energy levels and pulse irradiation of the physical subjects. It is well known also that a pair of the energy levels close to each other results into a new effect: The sinusoidal

Experimental realization of the porous silicon optical multilayers based on the 1-s sequence

We report experimental results of the reflectance spectra of deterministic aperiodic multilayer structures fabricated with porous silicon. The refractive index of the layers forming the structures follows the values generated by the self-similar sequence called “the 1s-counting sequence.” We fabricated samples with 64, 128, and 256 layers with different thicknesses and porosities by controlling the applied current density and the etching time. The measured reflectance spectra exhibit properties of self-similarity, which are in good agreement with theoretical results reported previously.

Electronic structure of cubic GaN/AlGaN quantum wells

For cubic AlxGa1−xN/GaN/AlxGa1−xN quantum wells we calculated the first energy transition 1h–1e as a function of x and the well width. The nearest neighbour empirical tight binding approximation, including spin-orbit interaction, together with the Surface Green Function Matching method is used.

Stark shift effects in rectangular and graded gap quantum wells

Abstract We study the Stark effect in rectangular quantum wells and in quantum wells with linear variation of the composition. The energies of the bound electronic states, the transition energies and their Stark shifts are calculated when a longitudinal electric field is applied. The spatial overlap of the electron and hole states and the intensity of the main optical transitions are considered, and their dependence on the electric field strength is discussed. We compare the Stark effect characteristics of the rectangular and graded composition quantum wells. Numerical calculations are performed within the framework of a semi-empirical sp 3 s∗ tight-binding model, the virtual crystal approximation and the surface Green function matching method. A comparison between the theoretical results and the experimental data available for these systems is made, and a critical discussion is presented.

Electronic states in near-surface quantum wells

Abstract We have calculated the energies and the spatial distributions of the electronic bound states of AlGaAs/GaAs near-surface quantum wells. We have employed a semi-empirical sp 3 s * tight-binding Hamiltonian including spin–orbit coupling, a Green function technique and the slab approximation. We have found blue shifts for the transition energies associated with the main optical transitions when the thickness of the AlGaAs top barrier decreases. The sign and the magnitude of these shifts agree quite well with the experimental data obtained recently. Both types of surface termination, cation and anion, are considered. In the case of As termination we have found a red shift for the transition energy of the first excited optical transition when the top barrier thickness decreases. An interpretation of these results in terms of the spatial distributions and orbital components of the electronic bound states is discussed.

Study of the electronic fundamental transition of zincblende InN/InGaN quantum wells

In this work we calculate the transition energy from the first level of holes to the first level of electrons (1h-1e) for cubic InN/InxGa1-xN quantum wells. We employ the empirical tight binding approach with a sp3s* orbital basis, nearest neighbors interactions and the spin-orbit coupling, together with the surface Green function matching method. Our tight binding parameters give a value of 0.65eV for the InN gap and 3.3eV for GaN. For the InxGa1-xN alloy we use the virtual crystal approximation. We study the transition energy behavior varying the well width for concentrations x=0.2, 0.5, and 0.8. For the calculations, we use two values of the valence band offset: 30% and 50%. We take into account the strain in the well, due to the different lattice constants between the well and the barrier.

Penetration of a symmetric light pulse through a wide quantum well

The reflection, transmission, and absorption of a symmetric electromagnetic pulse whose carrier frequency is close to the frequency of the interband transition in a quantum well are calculated. The energy levels in the quantum well are assumed to be discrete, and one excited level is taken into account. Consideration is given to the case of a sufficiently wide quantum well when the pulse wavelength corresponding to the carrier frequency is comparable to the quantum well width and when allowance should be made for the dependence of the matrix element of the interband transition on the photon wave vector. The calculations are performed with due regard for the difference between the refractive indices of the material of the quantum well and the barrier at an arbitrary ratio of the reciprocal radiative to nonradiative lifetimes of the excited level of the electronic system. It is demonstrated that the inclusion of the spatial dispersion and the difference in the refractive indices most strongly affects the reflection of the electromagnetic pulse, because the reflection due to interband transitions in the quantum well is accompanied by an additional reflection from the quantum well boundaries. Compared to the previously considered model, the most radical changes in the reflection are observed in the case when the reciprocal nonradiative lifetime of the excited state is substantially longer than the reciprocal radiative lifetime.

The role of spatial dispersion of an electromagnetic wave in its penetration through a quantum well

The theory of light penetration through a quantum well in a strong magnetic field perpendicular to the well plane is developed under the conditions where interband transitions occur in the well. The light wavelength is assumed to be comparable to the well width. The relationships for the reflection, absorption, and transmission are derived with due regard for the spatial dispersion of a monochromatic light wave and the difference between the refractive indices of the quantum well and the barrier. The normal incidence of light with respect to the well plane is considered, and one excited level is taken into account. It is demonstrated that the above two factors most strongly affect the reflection, because the reflection from the well boundaries appears in addition to the reflection caused by interband transitions in the quantum well. The most radical changes in the reflection are observed in the case when the reciprocal radiative lifetime of the excited state in the quantum well is short compared to the reciprocal nonradiative lifetime. In the range of large well widths, the applicability of the theory is limited by the existence condition of quantum well levels.