Semi-parabolic Quantum Research Articles

Theoretical study of nonlinear absorption of a strong electromagnetic wave in infinite semi-parabolic Plus Semi-inverse Squared Quantum Wells by using quantum kinetic equation

General analytic expressions for the total absorption coefficient of strong electromagnetic waves caused by confined electrons in Infinite semi-parabolic plus Semi-inverse Squared Quantum Wells (ISPSISQW) are obtained by using the quantum kinetic equation for electrons in the case of electron-optical phonon scattering. A second-order multi-photon process is included in the result. The dependence of the total absorption coefficient on the intensity E0, the photon energy ħΩ of an SEMW, and the temperature T for a specific GaAs/GaAsAl ISPPSISQW is achieved by using a numerical method. The computational results demonstrate that the total absorption coefficient’s dependence on photon energy can be utilized for optically detecting the electric sub-bands in an ISPPSISQW. Besides, we also give theoretical rules on the dependence of the Full Width at Half Maximum on important external parameters such as temperature and perpendicular magnetic field. Furthermore, the obtained results are consistent with prior theoretical and experimental findings.

Effect of parabolic structure potentials on electron mobility in AlxGa1-xAs quantum well based field effect transistor structure

Here, we theoretically calculate and analyze electron mobility μ in AlxGa1-xAs double parabolic and semi-parabolic quantum well (DPQW and DSPQW) based field effect transistor structures. We compute μ as a function of applied electric field F by considering ionized impurity (II) and alloy disorder (AL) screened scattering potentials (VscrII/AL) and show that μ(DPQW) > μ (DSPQW). The symmetric property of VscrII/AL makes μ to vary symmetrically around F = 0 at which two subbands are occupied. The shape of the DSPQW structure potential, compared to DPQW, causes the subband wave functions ψ0 and ψ1 to lie nearer and also penetrate more into the central barrier. Accordingly, the II-scattering is reduced due to increased distance of the electrons from the ionized donors (lying in the side barriers), while AL-scattering is enhanced through increased scattering in the central barrier. As a result, we obtain for F = 0, μII (DSPQW) > μII (DPQW) and μAL (DSPQW) < μAL (DPQW). Further, we show that μ enhances in DPQW by increasing design parameters such as well width, spacer width, and central barrier width. However, μ reduces with the increase in alloy concentrations inside the well through intersubband interaction. The obtained results reflect the suitability of parabolic potential based quantum well structures in emerging optoelectronic devices to enhance the transport and optical properties.

Magneto-optical absorption in an asymmetric finite quantum well

We examine the influence of internal (confinement frequency, Al-doped concentration, β parameter) and extrinsic (magnetic field, temperature) parameters on the energy differences and magneto-optical absorption properties of a finite semi-parabolic plus semi-inverse squared (FSPSISP) quantum well. Our results demonstrated that the energy difference between the ground and excited states is substantially dependent on the amount of Al-doped in the system, the confinement frequency, and the magnetic field, and slightly dependent on parameter characterizing the inverse squared part of the confinement potential, but not temperature. The magneto-optical absorption coefficient (MOAC) increases with confinement frequency, Al-doped concentration, magnetic field, and temperature, but decreases with β. The full width at half maximum (FWHM) increases with all parameters. By optimizing these parameters, we can enhance the MOAC. Our results provide deeper insight into the optical properties of low-dimensional systems with finite confinement potential.

Effects of external perturbations on light absorption by light/heavy hole excitons in a semi-parabolic quantum well

The effects of electric, magnetic, and intense terahertz laser fields on optoelectronic properties are investigated in a GaAs/AlxGa1-xAs semi-parabolic quantum well. The binding energy, exciton light absorption coefficients, interband transition energies, and dipole elements in the matrix are studied within the structure of the parabolic band and effective-mass approximations. The transition energy difference between the ground-state electron energy level and the ground-state heavy hole (light hole) energy level and matrix elements are carried out as functions of external perturbations with a constant well size. The results exhibit that the exciton binding energies of heavy and light holes reduce as long as the laser dressing parameter is larger. The optical absorption of light hole exciton in the system is stronger than the heavy hole exciton. And the excitonic energies, transition energies, and absorption coefficients are much more sensitive and controlled by changing the external perturbations.

Cyclotron resonance linewidth due to electron scattering by five different phonon modes in semiparabolic quantum wells

A theory of the cyclotron resonance absorption linewidth (CRALW) in the presence of electron scattering by five different phonon modes in a semiparabolic quantum well has been developed. The cyclotron resonance absorption power and the CRALW are calculated by use of the projection-operator and profile methods, respectively. The main results are as follows: The CRALW increases with increase of the confinement frequency, temperature, and magnetic field, but decreases with increase of the Landau level number for the interface mode, the bulk mode, and three types of confined modes. Besides, the CRALW is largest for the Huang-Zhu phonon model but is smallest for the bulk mode. The contributions of the interface modes to the CRAWL are considerable and should be taken into account in the cyclotron resonance effect. Moreover, as the Landau level number increases, both the CRALW and the difference in the CRALW between two Landau levels decrease. In addition, the agreement between the guided modes and the Huang-Zhu phonon model is better than that between the slab modes and the Huang-Zhu phonon model. Our theoretical calculations accord well with previous experimental data.

Intersubband absorption linewidth in a semi-parabolic quantum well: Comparison among three different phonon models

In this article, effects of different confined phonon models on intersubband absorption linewidth in semiparabolic quantum well (SPQW) is studied in detail through considering the optically detected magneto-confined phonon resonance (ODMCPR) effect. The projection operator and profile methods are utilized in order to calculate the linear conductivity tensor as well as magneto-phonon resonance absorption power (MPRAP) and measure the absorption linewidth or the full width at half maximum (FWHM) at the ODMCPR peak, respectively. We find that (i) the FWHM (absorption linewidth) as functions of the temperature, Landau level, and confining potential frequency; (ii) there is a different dependence in slab and guided phonon modes, as well as Huang–Zhu (HZ) phonon mode model on the FWHM; (iii) the confined phonon modes have great influence on the intersubband absorption linewidth in semiparabolic quantum well; (iv) the present calculations accord well with previous experimental studies.

Comparison of the magneto-optical properties of the semi-parabolic well with those of the parabolic and rectangular wells under the combined influences of aluminum concentration and hydrostatic pressure

In this paper, we report the comparison of the magneto-optical transport properties of the semi-parabolic potential quantum well with those of the parabolic and rectangular potential quantum wells under the combined influences of the aluminum concentration, the temperature, the hydrostatic pressure, and the Landau levels by using the methods of the quantum field theory for many-particle systems in statistical physics and the profile to calculate analytically the conductivity tensor expression, the magneto-optical absorption power expression of the optically detected magneto-phonon resonance (ODMPR) oscillation, and the full width at half maximum (FWHM) of the ODMPR peak, respectively, in quantum wells with three above different confining potential shapes for typical GaAs/AlxGa1−xAs material. The results obtained from the present study show that (i) the ODMPR peak position undergoes a red-shift as the aluminum concentration and the hydrostatic pressure increase while it experiences a blue-shift as the temperature augments for all three above confining potential shapes; (ii) the FWHM as functions of the barrier's Al-concentration, the system's temperature, and the hydrostatic pressure for all three confining potential shapes is presented to compare; (iii) the dependence of the FWHM on the barrier's Al-concentration and the hydrostatic pressure for the Landau levels for three confining potential shapes also is taken into account in detail; (iv) our present theoretical calculations are found to be consistent with previous experimental calculations.

Nonlinear magneto-optical absorption in a finite semi-parabolic quantum well

The magneto-optical absorption properties, including magneto-optical absorption coefficient (MOAC) and its line-width, or the full-width at half-maximum (FWHM), of a GaAs/Ga $$_{1-s}$$ Al $$_s$$ As quantum well with a finite semi-parabolic potential are studied under the combined effects of the Al-doped concentration (s), the hydrostatic pressure (P), and the temperature (T). The MOAC is expressed as a function of photon energy for distinct values of s, P, T, and the well-width $$(L_z)$$ when the electron-phonon interaction is included. The energy separation as well as the intensity and position of absorption peaks depend on these parameters. The variation of the FWHM of absorption peaks is used to study absorption characteristics as a function of s, P, T, and $$L_z$$ . The temperature-dependent FWHM is found to qualitatively consistent with experimental observations.

Cyclotron–interface phonon resonance line-width in asymmetric semiparabolic quantum wells

In this study, we investigated the cyclotron–interface phonon resonance line-width in GaAs/AlAs asymmetric semiparabolic quantum wells when electrons are scattered by symmetric (antisymmetric) interface optical phonons. The operator projection and profile methods were employed to calculate the expressions for the absorption power and the full width at half maximum (FWHM), respectively. We found that the electron–interface phonon interactions by the antisymmetric modes are weaker than those by the symmetric modes under all phonon emission and absorption cases. In addition, the FWHM is more dominant for interface phonon absorption compared with that for interface phonon emission. The interface optical phonon modes at the resonance peak with a lower-photon frequency are much more important for electron–interface optical phonon scattering than those at the resonance peak with a higher-photon frequency. Our results are consistent with previously reported experimental data.

Thermoelectric power hysteresis in semi-parabolic quantum well

The influence of semi-parabolic surface potential on quantum well thermoelectric power is investigated. The thermoelectric power dependence on the Fermi level and quantum well parameters is determined. It is shown that semi-parabolic quantum well thermoelectric power exhibits hysteresis features. The hysteresic loops and sign change in thermoelectric power dependence on the surface potential are ascribed to properties of electrons at the edges and electron localization.

Effects of temperature and hydrostatic pressure on the optical rectification associated with the excitonic system in a semi-parabolic quantum dot

Abstract The optical rectification for a GaAs quantum dot with an excitonic system is investigated for the various applied hydrostatic pressure, ambient temperature, and different effective size. The dependence of Optical Rectification Coefficient (ORC) on the temperature, radius and hydrostatic pressure in the strong confinement regime for both excitonic as well as without excitonic effects has been studied. This work demonstrates the intricate dependence of ORC on electron-hole pair localization, temperature change, alteration in radius and variation in hydrostatic pressure.

The effect of temperature, hydrostatic pressure and magnetic field on the nonlinear optical properties of AlGaAs/GaAs semi-parabolic quantum well

In this paper, we explore the optical properties of AlGaAs/GaAs semi-parabolic quantum well (QW) under different temperature, hydrostatic pressure and applied magnetic field. We calculate the nonlinear optical absorption coefficients and the refractive index changes (RICs) with the compact density-matrix approach and iterative method. Then, within the framework of the effective mass and parabolic-band approximations, the energy eigenvalues and the corresponding wave functions for semi-parabolic QW have been obtained by the finite difference method. The theoretical findings show that (1) the energy spectrum depends strongly on temperature, hydrostatic pressure and applied magnetic field; (2) the linear and third-order nonlinear optical absorption coefficients and the RICs are quite sensitive to temperature, hydrostatic pressure and applied magnetic field. Our study provides a theoretical basis for the fabrication of QW structure.

Semi-parabolic quantum well electrical conductivity

The paper reports the development of a model for the conductivity across a semi-parabolic quantum well and numerical results obtained with this model. The scattering mechanism effect on the electrical conductivity is examined. For polar optical phonon scattering the electrical conductivity is found to be non-monotonic with the quantum well width, which is attributed to delocalization of electrons.

Two-photon induced magneto-optical absorption in finite semi-parabolic quantum wells

Abstract We theoretically study the magneto-optical absorption in a GaAs/Ga 1 − s Al s As finite semi-parabolic quantum well where the two-photon process and electron–LO-phonon interaction have been included. The energy separation increases with Al-concentration and the field but decreases with the well-width. The peaks positions of the magneto-optical absorption coefficients (MOAC) present a blue-shift with Al-concentration and the magnetic field, a red-shift with the well-width, but is independent of the temperature. The MOAC peaks intensities increase monotonically with the field and temperature but are the non-monotonic functions of Al-concentration and well-width. The full-width at half-maximum (FWHM) decreases with the well-width but increases with all other parameters. The T -dependent FWHM is found to be in good agreement with previous theoretical and experimental results. Moreover, we found two rules describing the Al-concentration and the well-width dependent FWHM which require an experimental work to verify its correctness.

Magneto-optical effect in GaAs/GaAlAs semi-parabolic quantum well

We theoretically study the combined effect of Al-concentration, hydrostatic pressure, and temperature on the magneto-optical absorption properties of a semi-parabolic quantum well (SPQW) by investigating the magneto-optical absorption coefficient (MOAC) and the full-width at half-maximum (FWHM). The expression of MOAC is expressed by the second-order golden rule approximation where the electron–longitudinal-optical (LO) phonon interaction is taken into account while the FWHM is obtained from the profile of the curves. The numerical calculations are made for a typical GaAs/GaAlAs quantum well. Our results showed that the Al-concentration, hydrostatic pressure, and temperature affect the magneto-optical absorption properties strongly. Threshold energy and the resonant peaks are non-monotonic functions of the Al-concentration. Moreover, it has been revealed that the magneto-optical absorption properties of SPQW can be controlled by changing these parameters.

Linear and nonlinear optical absorptions in III–V nitrides quantum well with semi-parabolic confining potential

Linear and third-order nonlinear optical absorptions in III–V nitrides semi-parabolic quantum wells are investigated. The analytical expression of linear and third-order nonlinear optical absorption coefficients is obtained by using compact density matrix approach and iterative method. Our results show that the optical absorption coefficients are strongly influenced by confinement frequency and electric fields. Moreover, the optical absorption coefficients also sensitively depend on the relaxation time of the systems. However, the influences of the involved parameters for the linear optical absorption, third-order nonlinear optical absorption, and the total optical absorption are different.

Influence of the position dependent effective mass on the nonlinear optical properties in semiparabolic and parabolic quantum well with applied magnetic field

In the current work, the nonlinear optical properties in GaAs/Ga1−xAlxAs semiparabolic and parabolic quantum well(QW) with constant effective mass(CEM) and position dependent effective mass(PDEM) are estimated for different applied magnetic field. In this regard, we have obtained the analytical expressions of the nonlinear rectification(OR), second harmonic generation(SHG), third harmonic generation(THG), optical absorption coefficients(OACs), and refractive index changes(RICs) by using the compact density matrix formalism. Simultaneously, we obtain the reliable energy eigenvalues and their corresponding eigenfunctions via the finite difference method. According to the obtained results, it is found that: (1)the correct inclusion of PDEM is the cause of a noticeable difference in nonlinear optical properties with respect to the use of CEM. (2)the applied magnetic field bear substantial technological importance in the process of nonlinear optical properties modulation.

Linear and nonlinear optical absorption coefficient and electronic features of triple GaAlAs/GaAs and GaInAs/GaAs quantum wells depending on barrier widths

In the present work, the effect of the barrier widths (BWs) on the linear and nonlinear optical absorption coefficient (OAC) and the electronic features of asymmetric triple Ga1-xAlxAs/GaAs (A structure) and Ga1-xInxAs/GaAs (B structure) quantum wells (QW) was investigated. The wave-functions and energy levels of asymmetric triple quantum wells (ATQW) consisting of inverse semi V-shaped, inverse semi parabolic and semi parabolic quantum well were analyzed by solving the Schrödinger equation, using the effective mass approach. As the electrons in the ground state are mostly located into the semi-parabolic quantum well, they are less affected by BWs. However, the electrons in the second and third states show a great change due to the increase in BW between them. Our results present that the potential height, the energy levels and the energy differences of A structure are always lower than of B structure. Also, the linear and nonlinear OACs depend on BWs. The absorption spectrum of the intersubband indicates blue or red shifts, as the energy interval changes with BWs. Therefore, the variation of these coefficients, which may be suitable for various optical modulators and infra-red optical device applications, can be smoothly achieved by replacing BWs.

Optical properties in GaAs/AlGaAs semiparabolic quantum wells by the finite difference method: Combined effects of electric field and magnetic field

In the present work, the optical properties of GaAs/AlGaAs semiparabolic quantum wells (QWs) are studied under the effect of applied electric field and magnetic field by using the compact-density-matrix method. The energy eigenvalues and their corresponding eigenfunctions of the system are calculated by using the differential method. Simultaneously, the nonlinear optical rectification (OR) and optical absorption coefficients (OACs) are investigated, which are modulated by the applied electric field and magnetic field. It is found that the position and the magnitude of the resonant peaks of the nonlinear OR and OACs can depend strongly on the applied electric field, magnetic field and confined potential frequencies. This gives a new way to control the device applications based on the intersubband transitions of electrons in this system.

Polar charges effect on multisubband electron mobility in the semiparabolic quantum wells based on AlN/AlGaN/AlN

This work presents multisubband electron mobility in the polarization semi-parabolic quantum wells (SPQWs) AlN/AlxGa1−xN/AlN. First, a theory of multisubband mobility between the lowest two subbands under a uniform external electric field is studied. By using the variation method, the one-dimensional Poisson and Schrödinger equations have been solved within a finite potential barrier model and a bent band figured by all confinement sources (realistic model). Then, we computed and discussed about the effective confining potential profile, the wave function and multisubband mobility. Our result shows that the positive interface polarization charges effect on the distribution of the two-dimensional electron gas (2DEG) in SPQWs so it has great influences on multisubband mobility.