Semi-parabolic Quantum Research Articles

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.

Exciton effects on the nonlinear optical properties of semiparabolic quantum dot under electric field

The effects of exciton and electric field on the nonlinear optical properties, such as refraction index change, optical absorption coefficient and optical rectification of semiparabolic one-dimensional quantum dot, were theoretically investigated. The energy eigenvalues and eigenfunctions are calculated numerically within the effective mass approximation for a typical GaAs/ Al0.3Ga0.7 As quantum dot, for the cases where there is an exciton or a single electron/hole in the structure. Optical properties are obtained using the compact density matrix approach and steady state solutions. Our results show that: i) if the increasing electric field is oriented along the growth direction, the refractive index change structure and the resonance peaks of the absorption coefficient and optical rectification present a blue shift and are weakened for exciton and electron systems but have a red shift and are strengthened for the hole system; ii) when the field, oriented against the growth direction, augments, the above optical parameters present a red shift and are increased for exciton and electron systems but have a blue shift and are lowered for the hole system; iii) the exciton presence in the structure enhances the amplitude of the resonant peaks of all optical parameters even at zero electric field.

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 optical rectification and second-harmonic generation in a semi-parabolic quantum well under intense laser field: Effects of electric and magnetic fields

The effects of electric and magnetic fields on the nonlinear optical rectification and second harmonic generation coefficients related with intersubband transitions in a semi-parabolic quantum well under intense laser field are theoretically studied. The energy levels and corresponding wave functions are obtained by solving the conduction band Schrödinger-like equation in the parabolic approximation and the envelope function approach. Numerical calculations are presented for a typical GaAs/Ga1-xAlxAs quantum well. The results show that both the non-resonant intense laser field and the static external fields have significant influences on the magnitude and resonant peak energy positions of the coefficients under study.

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.

Optical absorptions in asymmetrical semi-parabolic quantum wells

Optical absorptions in semi-parabolic quantum wells are investigated. By using density-matrix approach and iterative procedure, the analytical formula of optical absorption coefficients in this semi-parabolic quantum wells are deduced. The numerical results on typical GaAs/AlGaAs materials are calculated. The relations between the optical absorptions and the quantum confinement from the semi-parabolic quantum wells, the incident optical intensity, and the relaxation rate are investigated. The results indicate that the absorption peaks bule-shift and the values of the peaks increase with the enhancement of the parabolic confining frequency. The values of the absorption peaks increase quickly with the increase of the relaxation time. In addition, the total absorption coefficient decrease with the increase of the incident optical intensity.

Radiative lifetime of barbell excitons in semiparabolic double quantum wells under intense laser fields

The binding energy and optical properties of barbell excitons in GaAs–Ga1−xAlxAs semiparabolic double quantum wells under intense laser fields are investigated. Calculations are performed within the effective mass and envelope-function approximations, including the conduction band nonparabolicity. The dependence of the binding energy, oscillator strength and exciton absorption spectrum on the laser field in symmetric and asymmetric quantum wells is studied by using a finite difference method. It is shown that the exciton radiative lifetime can be tuned to a large extent by a proper choice of the structure design (double well size, middle barrier position and its thickness) as well as by varying the laser field intensity.

Electronic Raman scattering in double semi-parabolic quantum wells

The differential cross-section for electronic Raman scattering in double semi-parabolic quantum wells of typical GaAs/AlxGa1−xAs is investigated numerically with the effective-mass approximation. The dependence of the differential cross-section on structural parameters such as the barrier width and the well widths is studied. Our results indicate that the electronic Raman scattering is affected by the geometrical size and can be negligible in the symmetric double-well case.

Magnetic Field Effects on the Optical Properties of Double Semi-Parabolic Quantum Wells

Magnetic Field Effects on the Optical Properties of Double Semi-Parabolic Quantum Wells

Second harmonic generation in asymmetric double semi-parabolic quantum wells: Effects of electric and magnetic fields, hydrostatic pressure and temperature

The second harmonic generation (SHG) of a typical GaAs/Ga1−xAlxAs asymmetric double semi-parabolic quantum wells (DSPQWs) is investigated numerically. The SHG is obtained using the compact density matrix approach. In this work, the effects of the structure parameters, the applied electric and magnetic fields, the hydrostatic pressure and temperature on the SHG coefficient of the asymmetric DSPQWs are studied. Our calculations show that the resonant peaks of the SHG experience an obviously blue-shift and decrease in the magnitude with increasing barrier height. The major-resonant peak value of the SHG is a non-monotonic function of the barrier width and decreases with increase in the right-well width. The results show that the applied electric and magnetic fields affect the magnitude and position of the resonant peaks. Moreover, the resonant peaks of the SHG experience a red-shift (blue-shift) and decrease (increase) in magnitude monotonically with increasing pressure (temperature).

Electric field effects on the linear and nonlinear intersubband optical properties of double semi-parabolic quantum wells

In this work, the effects of the electric field on the optical properties of the symmetric and asymmetric double semi-parabolic quantum wells (DSPQWs) are investigated numerically for typical GaAs/Al x Ga 1− x As. Optical properties are obtained using the compact density matrix approach. Our calculations for the asymmetric DSPQW show that the resonant peak values of the total refractive index change and total optical absorption coefficient are maximum for a certain value of the applied electric field, due to the anti-crossing effect. However, for the symmetric DSPQW, the resonant peak values of these optical properties decrease monotonically with increasing the applied electric field. Also, our results indicate that a larger value of the optical rectification coefficient of the symmetric DSPQW can be induced by applying a small electric field.

Effects of external electric and magnetic fields on the linear and nonlinear intersubband optical properties of finite semi-parabolic quantum dots

In this work, influences of external electric and magnetic fields on the optical rectification coefficient, the linear and the third-order nonlinear optical absorption coefficients as well as refractive index changes of finite semi-parabolic quantum dots are investigated. In this regard, energy eigenvalues and eigenfunctions of the system are calculated numerically, and optical properties are obtained using the compact density matrix approach. The results show that external electric and magnetic fields have a great influence on these optical quantities.

Optical Rectification and Second Harmonic Generation of Finite and Infinite Semi-Parabolic Quantum Wells

Optical Rectification and Second Harmonic Generation of Finite and Infinite Semi-Parabolic Quantum Wells

Intense laser field effects on the linear and nonlinear intersubband optical properties of a semi-parabolic quantum well

By using the compact-density matrix approach, the effect of a nonresonant intense laser field on the linear and nonlinear optical absorptions based on intersubband transitions and the refractive index changes in an asymmetric semiconductor quantum well have been presented. Our results show that the peak position of the absorption coefficient is sensitive to intense laser field, the absorption maximum shifts towards lower energies for increasing intense laser field value. Also we observe as the intense laser field strength increases, the total refractive index change has been increased in magnitude and also shifted towards lower energies. The results indicate that linear and nonlinear optical properties of the low dimensional semiconductor heterostructures can be adjusted in a desired energy range by using intense laser field.

LINEAR AND NONLINEAR INTERSUBBAND OPTICAL ABSORPTION OF FINITE AND INFINITE SEMI-PARABOLIC QUANTUM WELLS

In this work, the optical absorption coefficients and the refractive index changes for the infinite and finite semi-parabolic quantum well are calculated. Numerical calculations are performed for typical GaAs / Al x Ga 1-x As semi-parabolic quantum well. The energy eigenvalues and eigenfunctions of these systems are calculated numerically. Optical properties are obtained using the compact density matrix approach. Results show that the energy eigenvalues and the matrix elements of the infinite and finite cases are different. The calculations reveal that the resonant peaks of the optical properties of the finite case occur at lower values of the incident photon energy with respect to the infinite case. Results indicate that the maximum value of the refractive index changes for the finite case are greater than that of the infinite case. Our calculations also show that in contrast to the infinite case, the resonant peak value of the total absorption coefficient in the case of the finite well is a non-monotonic function of the semi-parabolic confinement frequency.

Linear and nonlinear intersubband optical absorption and refractive index changes of asymmetric double semi-parabolic quantum wells

The optical properties of the asymmetric double semi-parabolic quantum wells (DSPQWs) are investigated numerically for typical GaAs/Al x Ga 1− x As. Optical properties are obtained using the compact density matrix approach. In this work, effects of the structure parameters such as the barrier width and the well widths on the optical properties of the asymmetric DSPQWs are investigated. The results show that the linear and nonlinear optical properties of asymmetric DSPQW are non-monotonic functions of these structure parameters. The behavior of the refractive index changes of asymmetric DSPQW with the variation of the barrier width is different substantially with that of symmetric DSPQW. Results reveal that the resonant peak values of the total absorption coefficient of asymmetric DSPQW is usually greater than that of symmetric DSPQW. Our calculations also show that the total absorption coefficient of asymmetric DSPQW is larger than that of asymmetric double square quantum well.