Semi-parabolic Quantum Wells 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.

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.

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.

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.

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.

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.

Linear intersubband optical absorption in the semiparabolic quantum wells based on AlN/AlGaN/AlN under a uniform electric field

The linear intersubband optical absorption in the polarization semiparabolic quantum wells (SPQWs) are investigated for typical AlN/AlxGa 1−x N/AlN. First, the one-dimensional Poisson and Schrödinger equations have been solved by the variational method within a finite potential barrier model and a bent band figured by all confinement sources (realistic model). Then, the intersubband optical absorption between the lowest two subbands has been theoretically studied under an uniform external electric field. Computed results including the effective confining potential profile, the wave function and the distribution of electron gas in quantum wells, intersubband optical absorption coefficient have been discussed. Our calculation shows that the positive interface polarization charges affect on the distribution of the two-dimensional electron gas (2DEG) in SPQWs so it has great influences on the total optical absorption coefficients significantly.

Electric and intense laser field effect on the electronic properties of Ga1−x Al x As/GaAs and Ga1−x ln x As/GaAs semi-parabolic quantum wells

In the present study, the electronic properties of Ga1−x Al x As/GaAs and Ga1−x ln x As/GaAs semi-parabolic quantum wells (SPQWs) are theoretically investigated as dependent on the intense laser field (ILF) and the electric field within the effective mass. All results show that the shape of the confined potential profile, the energy differences and the dipole moment matrix elements are varied as dependent on ILF and the applied electric field. The energy levels of different SPQWs give different results by varying ILF amplitudes and electric field. In the case of SPQW under ILF and the electric field, there are important modifications of the electrical states of SPQWs, due to the effects of confining the potential resulting from the applied electric field and ILF. The numerical results show that these applied fields have a significant effect on the electronic characteristics of SPQW structures. It is seen that the finding probabilities of the electrons in Ga1−x Al x As/GaAs SPQW are more than Ga1−x In x As/GaAs SPQW. Highlights The shape of SPQWs changes as dependent on ILF. The potential profile of SPQWs depends on the size and direction of the applied electric field. The energy level and the dipole matrix element vary with the changes in SPQW. The probability density for F = ‒30 kV cm−1 are greater both F = 0 and F = 30 kV cm−1 for both SPQWs. The finding probabilities of electrons in SPQWs under ILF are more than for zero ILF.

Nonlinear optical absorption via two-photon process in asymmetrical semi-parabolic quantum wells

The nonlinear optical absorption properties via two-photon process of an asymmetrical semi-parabolic quantum well (ASPQW) has been theoretically investigated. The analytical expression for the magneto-optical absorption coefficient (MOAC) is obtained by relating it to the transition probability for the absorption of photons. Meanwhile, the half width at half maximum (HWHM) of the resonant peaks is gained by the profile method. The numerical results are calculated for typical GaAs and GaAs/GaAlAs quantum wells. The obtained results show that MOAC and HWHM are strongly dependent on confinement frequency, magnetic field and temperature in both one- and two-photon processes. The increasing behavior of HWHM on temperature is generally in good accord with the previous reported ones, both theoretically and experimentally.

Electric field effect on the second-order nonlinear optical properties in semiparabolic quantum wells

Electric field effect on the second-order nonlinear optical properties in semiparabolic quantum wells are studied theoretically. Both the second-harmonic generation susceptibility and nonlinear optical rectification depend dramatically on the direction and the strength of the electric field. Numerical results show that both the second-harmonic generation susceptibility and nonlinear optical rectification are always weakened as the electric field increases where the direction of the electric field is along the growth direction of the quantum wells, which is in contrast to the conventional case. However, the second-harmonic generation susceptibility is weakened, but the nonlinear optical rectification is strengthened as the electric field increases where the direction of the electric field is against the growth direction of the quantum wells. Also it is the blue (or red) shift of the resonance that is induced by increasing of the electric field when the direction of the electric field is along (or against) the growth direction of the quantum wells. Finally, the resonant peak and its corresponding to the resonant energy are also taken into account.

The second-harmonic generation susceptibility in semiparabolic quantum wells with applied electric field

The second-harmonic generation susceptibility in semiparabolic quantum wells with applied electric field is investigated theoretically. For the same topic studied by Zhang and Xie [Phys. Rev. B 68 (2003) 235315] [1], some new and reliable results are obtained by us.It is easily observed that the second harmonic generation susceptibility decreases and the blue shift of the resonance is induced with increasing of the frequencies of the confined potential. Moreover, a transition from a two-photon resonance to two single-photon resonances will appear adjusted by the frequencies of the confined potential. Similar results can also be obtained by controlling the applied electric field. Surprisingly, the second harmonic generation susceptibility is weakened in the presence of the electric field, which is in contrast to the conventional case. Finally, the resonant peak and its corresponding resonant energy are also taken into account.

Nonlinear intersubband optical absorption in semiparabolic quantum wells

The linear and third-order nonlinear optical absorptions in semiparabolic quantum wells are studied in detail. Analytic formulas for the linear and third-order nonlinear optical absorption coefficients are obtained using the compact density matrix approach. Based on this model, numerical results are presented for typical GaAs/AlGaAs semiparabolic quantum wells. The results show that the factors of the incident optical intensity and the semiparabolic confinement frequency have great influences on the total optical absorption coefficients.

Electric field effect on the nonlinear optical rectification properties in III–V nitrides semi-parabolic quantum well

By using the compact-density-matrix approach and iterative procedure, a detailed procedure for the calculation of the optical rectification (OR) tensor is given in the electric-field-biased semi-parabolic quantum wells (QW's). The simple analytical formula for the OR coefficient in the systems is also deduced. By adopting the methods of envelope wave function and the displaced harmonic oscillator approach, the electronic states in semi-parabolic QW's with applied electric fields are exactly solved. Numerical results on typical Al x Ga 1-x N / GaN materials show that, nonlinear OR coefficient is strongly affected only by the confinement frequency ω0, the applied electric field. Moreover, OR also sensitively depends on the relaxation rate of the systems.