Asymmetric Double Quantum Wells Research Articles

Second harmonic generation in Harmonic-Gaussian asymmetric double quantum well: effect of magnetic and intense laser fields

We have theoretically analyzed the effects of externally applied fields (magnetic and intense laser) as well as various structural parameters such as well width, barrier width, barrier height, and structural asymmetry on the second harmonic generation (SHG) coefficients of GaAs/Al0.3Ga0.7As Harmonic-Gaussian asymmetric double quantum wells (QW). The time-independent Schrödinger equation was solved using the diagonalization method and effective mass approximation to obtain the energy eigenvalues and eigenfunctions of the structure. An expression derived within the compact density matrix approach has been used to evaluate the second harmonic generation (SHG) coefficient. Our numerical results indicate that increasing the magnitude of the magnetic (intense laser) field causes the peak positions of SHG to shift towards higher energy regions/blue (lower energy regions/red). On the other hand, as the structural parameters A1 and A2 ( k and z0 ) increase, the peak positions of the SHG coefficients exhibit a shift towards higher energy regions/blue (lower energy regions/red). We expect that the results of our study will contribute to the development of new optoelectronic devices based on the Harmonic-Gaussian asymmetric double quantum well structure.

Hydrostatic pressure and temperature effects on nonlinear optical properties in harmonic-Gaussian asymmetric double quantum wells

The paper examines the linear and non-linear optical characteristics of an electron in harmonic Gaussian asymmetrical double quantum wells, taking into account thermodynamic variables such as temperature and hydrostatic pressure. Numerical calculations by considering the effective mass and parabolic band approximation are performed. The electron contained within an asymmetric double well generated by the sum of a parabolic and Gaussian potential has its eigenvalues and eigenfunctions determined using the diagonalization approach. For nonlinear optical coefficients, the density matrix expansion is used. Wavefunctions and energy levels vary as an effect of the applied fields. In harmonic Gaussian asymmetrical double quantum wells, the total optical absorption coefficient (TOAC), the relative refractive index changes (RRIC), and second harmonic generation (SHG) have all been theoretically investigated. The magnitude and position of the resonant peaks are significantly influenced by the hydrostatic pressure and temperature effects. With controllable coupling and externally applied hydrostatic pressure and temperature, the potential model presented in this study can be used to simulate and manipulate the optical and electronic properties of the asymmetric double-quantum heterostructures, such as double quantum dots and wells.

Optical rectification and second harmonic generation in CdSe/MgSe asymmetric double quantum wells

In this study, we report theoretically the effect of well, barrier widths and polarization on optical properties of intersubband transitions (ISBT) in CdSe/MgSe asymmetric quantum wells (ADQWs). Eigenenergies and their corresponding wave functions have been calculated by solving numerically the Schrödinger equation. The second harmonic generation and the optical rectification including intersubband transition energies have been discussed. Obtained results revealed that intersubband transition depends strongly on the quantum wells and the barrier widths as well as the stark effect. With appropriate intensity, optical rectification can reach great magnitude. We hope that the numerical results of our research are valuable theoretically and experimentally to our scientific community in nonlinear optics.

The influence of screening function on exciton mott transition in an asymmetric double quantum well

The semiconductor-to-metal transition (SMT) due to excitons exciton mott transition (EMT) in GaAs/Al[Formula: see text]Ga[Formula: see text]As asymmetric double quantum well (ADQW) has been studied theoretically by tuning direct (DX) and indirect (IDX) exciton densities using variation technique combined with the Monte Carlo approximation. The interaction of the optically pumped exciton densities is accounted for through the Thomas–Fermi (TF) dielectric screening and compared with Hartree–Fock (HF) screening. The screening effects of IDX at the barrier regime have been accounted for through size-dependent screening. The important characteristics of EMT, such as (i). binding energy and (ii), diamagnetic susceptibility have been studied in both coupled ([Formula: see text]Å) and isolated ([Formula: see text]Å) regimes of ADQW. The effect of asymmetry on the EMT of DX (IDX) is significant only for [Formula: see text] in the case of the coupled regime of ADQW, which may be due to the dynamic tunneling mechanism. The impact of the screening among the exciton densities to bring out the avalanche breakdown of excitons at the critical concentration has been studied for different kinds of excitons.

Effects of the Magnetic Field and Thickness of Layers on Intersubband Absorption in Asymmetric Double Parabolic Quantum Wells

Effects of the Magnetic Field and Thickness of Layers on Intersubband Absorption in Asymmetric Double Parabolic Quantum Wells

Stabilization of modulation instability by control field in semiconductor quantum wells

This article explores the modulation instability of a continuous or quasi-continuous weak probe pulse in a three-level asymmetric double quantum wells under an electromagnetically induced transparency regime, controlled by a strong laser beam. The dynamics of modulation instability reveals that the instability gain as well as its bandwidth is greatly influenced by control field Rabi frequency. The probe pulse is found to be almost stable against modulation instability for higher values of control field Rabi frequency. The results of this investigation may potentially apply for oscillation free generation of supercontinuum in quantum well nanostructures.

Parabolic-Gaussian Double Quantum Wells under a Nonresonant Intense Laser Field.

In this paper, we investigate the electronic and optical properties of an electron in both symmetric and asymmetric double quantum wells that consist of a harmonic potential with an internal Gaussian barrier under a nonresonant intense laser field. The electronic structure was obtained by using the two-dimensional diagonalization method. To calculate the linear and nonlinear absorption, and refractive index coefficients, a combination of the standard density matrix formalism and the perturbation expansion method was used. The obtained results show that the electronic and thereby optical properties of the considered parabolic-Gaussian double quantum wells could be adjusted to obtain a suitable response to specific aims with parameter alterations such as well and barrier width, well depth, barrier height, and interwell coupling, in addition to the applied nonresonant intense laser field.

Harmonic-Gaussian Symmetric and Asymmetric Double Quantum Wells: Magnetic Field Effects

In this study, we considered the linear and non-linear optical properties of an electron in both symmetrical and asymmetrical double quantum wells, which consist of the sum of an internal Gaussian barrier and a harmonic potential under an applied magnetic field. Calculations are in the effective mass and parabolic band approximations. We have used the diagonalization method to find eigenvalues and eigenfunctions of the electron confined within the symmetric and asymmetric double well formed by the sum of a parabolic and Gaussian potential. A two-level approach is used in the density matrix expansion to calculate the linear and third-order non-linear optical absorption and refractive index coefficients. The potential model proposed in this study is useful for simulating and manipulating the optical and electronic properties of symmetric and asymmetric double quantum heterostructures, such as double quantum wells and double quantum dots, with controllable coupling and subjected to externally applied magnetic fields.

Tunneling dynamics and transport in MBE-grown GaAs/AlGaAs asymmetric double quantum wells investigated via photoluminescence and terahertz time-domain spectroscopy

Tunneling dynamics and transport in MBE-grown GaAs/AlGaAs asymmetric double quantum wells investigated via photoluminescence and terahertz time-domain spectroscopy

Dynamics of nonlinear optical rectification, second, and third harmonic generation in asymmetric triangular double quantum wells due to static electric and magnetic fields

Dynamics of nonlinear optical rectification, second, and third harmonic generation in asymmetric triangular double quantum wells due to static electric and magnetic fields

Carrier dynamics of AlGaAs/AlAs asymmetric double quantum wells with different barrier thickness

Optical properties and carrier dynamics of AlGaAs/AlAs asymmetric double quantum wells (ADQWs) with varied barrier thickness are studied by excitation-power-dependent photoluminescence (PL) and temperature-dependent time-resolved PL (TRPL) experiments. The origin of the transition energies derived from the time-integrated spectra is confirmed by theoretical calculation using the Schrödinger equation. The carrier kinetics and the temporal behavior of the emission in the narrow well (NW) and wide well (WW) are physically revealed with varying barrier thicknesses by the TRPL measurements. For a better understanding of the carrier transport mechanism, the electron tunneling times for the ADQWs are theoretically estimated based on a rate-equation model. The calculation indicates that the electron tunneling time decreases with increasing temperature, which may be induced by enhanced phonon-assisted scattering.

Photoluminescence of Double Quantum Wells: Asymmetry and Excitation Laser Wavelength Effects

Circularly polarized photoluminescence (PL) spectroscopy measured at 19 K on GaAs/AlGaAs symmetric and asymmetric double quantum wells (DQW) is reported. The PL is obtained by exciting the sample with a circularly polarized (left or right) laser in order to create an initial unbalanced distribution of electron spins in the conduction band and, in this way, obtain the electron spin lifetime . The effects of the excitation laser wavelength are estimated by exciting with laser wavelengths of 701.0, 787.0, 801.5, and 806.5 nm. The increase of with the excitation wavelength is attributed to the lower initial quasimomentum k of the excited carriers, which also reduces spin–orbit relaxation processes. is found to be higher in asymmetric DQWs: this is attributed to the wider QWs in these samples, which reduces spin relaxation due to the Dresselhaus mechanism. In addition, a smaller contribution from the Rashba mechanism is also detected by comparing samples with built‐in electric fields of different orientations defined by doped barrier layers.

Analysis of electric-field domain formations and carrier transport phenomena in GaAs/AlAs asymmetric double-quantum-well superlattices

We evaluated the formation of electric-field domains (EFDs) in three kinds of asymmetric double-quantum-well (ADQW) superlattices (SLs) whose photoluminescence (PL) properties revealed various characteristics affected by EFD formation. In particular, anomalous comb-shaped PL branches were clearly observed. Each PL branch corresponds to one EFD, giving important information on EFD distribution in ADQW-SLs. We determined the strengths of all electric-fields in all the EFDs from their redshifted PL signals and plotted their reverse bias voltage dependence. We clearly identified the EFD distributions in the ADQW-SLs in which the resonant tunneling effect plays an important role to make carrier transport paths. These results demonstrate that the analysis of EFD distributions from PL properties is an effective tool to investigate the carrier transport phenomena in biased SLs.

Nonlinear optical properties in AlxGa1-xAs/GaAs double-graded quantum wells: The effect of the structure parameter, static electric, and magnetic field

We present a theoretical simulation of the impact of applied external electric and magnetic fields, as well as of the change in structure parameters, on the nonlinear optical rectification (NOR), second harmonic generation (SHG), and third harmonic generation (THG) in typical GaAs/GaAlAs asymmetric double graded quantum wells (ADGQWs). At first, we have calculated the wave functions and the subband energy levels for the lowest bounded four states confined within the structure by solving the Schrödinger equation using the diagonalization method within the framework of the effective mass and single parabolic band approximations. Then, analytical expressions for the NOR, SHG, and THG that arise from the compact density matrix approach are used to evaluate the corresponding coefficients. The simulation results show that the applied external fields and the structure parameters play an important role in the optical properties of ADGQWs.

The effects of external fields on double GaAs/AlGaAs quantum well with Manning potential

In this paper, we calculated the electronic and optical absorption coefficient of the Manning-like double quantum well under the external applied electric and magnetic fields. To calculate the linear and third-order nonlinear optical absorption coefficients is used two-level approach in the density matrix expansion. The findings show that the electronic structure can be adjusted by changing the well and barrier widths, the well depth, the coupling between the wells as well as applied external field intensities. In addition, direct and indirect exciton states in asymmetric double quantum wells with Manning-like potential under electric field are compared with experimental studies. From the obtained results, it is concluded that the Manning-like potential is an excellent strategy for modeling electronic states in asymmetric double quantum wells with steep potential barriers and also the Manning-like potential allows modeling interdiffusion effects at the interfaces of multiple heterostructures.

Influence of hydrostatic pressure, temperature, and terahertz laser field on the electron-related optical responses in an asymmetric double quantum well

Influence of hydrostatic pressure, temperature, and terahertz laser field on the electron-related optical responses in an asymmetric double quantum well

Enhanced fifth-order nonlinearity with competing linear and nonlinear susceptibility via Fano interference

Enhanced fifth-order nonlinearity with Fano interference is theoretically studied in asymmetric double quantum wells. The resonant tunneling induces constructive interference for third- and fifth-order nonlinearities. Their competition causes a transparency window at some frequency detuning, where the fifth-order refractive index can be simultaneously enhanced by Fano interference. Simulation results show that fifth-order nonlinearity can be enhanced by about 10 times compared to that without the Fano effect. Also, the influence of different strengths of resonant tunneling coupling and Fano interference on enhanced high-order nonlinearity is discussed.

Optical anisotropies of asymmetric double GaAs (001) quantum wells

In the present work, we were able to identify and characterize a source of in-plane optical anisotropies (IOAs) occurring in asymmetric double quantum wells (DQWs), namely a reduction of the symmetry from ${D}_{2d}$ to ${C}_{2v}$ as imposed by asymmetry along the growth direction. We report on reflectance anisotropy spectroscopy (RAS) of double GaAs quantum well structures coupled by a thin ($<2$ nm) tunneling barrier. Two groups of DQW systems were studied: one where both QWs have the same thickness (symmetric DQW) and another where they have different thicknesses (asymmetric DQW). RAS measures the IOAs arising from the intermixing of the heavy and light holes in the valence band when the symmetry of the DQW system is lowered from ${D}_{2d}$ to ${C}_{2v}$. If the DQW is symmetric, residual IOAs stem from the asymmetry of the QW interfaces, e.g., that associated with Ga segregation into the AlGaAs layer during the epitaxial growth process. In the case of an asymmetric DQW with QWs with different thicknesses, the AlGaAs layers (that are sources of anisotropies) are not distributed symmetrically at both sides of the tunneling barrier. Thus the system loses its inversion symmetry, yielding an increase in the RAS strength. The RAS line shapes were compared with reflectance spectra in order to assess the heavy- and light-hole mixing induced by the symmetry breakdown. The energies of the optical transitions were calculated by numerically solving the one-dimensional Schr\"odinger equation using a finite-difference method. Our results are useful for interpretation of the transitions occurring in both symmetric and asymmetric DQWs.

Effect of barrier width between GaAs/InGaAs/GaAs double coupled quantum wells on bipolar transport and terahertz radiation by hot carriers in lateral electric field

The dependences of the current and integral intraband terahertz electroluminescence intensity on the electric field in the n-InGaAs/GaAs heterostructures with asymmetric double tunnel-coupled quantum wells under the conditions of bipolar lateral transport are established to differ qualitatively for different interwell barrier widths. In the case of the thick (∼50 Å) barriers at electric fields less than those corresponding to the Gunn instability, high-frequency current oscillations are observed, and the emission intensity monotonously increases with increasing electric field strength over the entire studied range up to 3 kV/cm. At small barrier widths (∼30 Å), the current oscillations are practically absent, and the emission intensity substantially increases with the field strength between 1.5 and 2 kV/cm. The emission intensity increase is explained by the addition of direct electron and hole transitions between the size-quantization subbands to the indirect intrasubband transitions. The observed differences may be explained by the different relationships between the interband radiative recombination time of the minority charge carriers (holes) in the narrow wells and the hole tunneling time into the wide wells, dependent on the interwell barrier width.

Heavy and light exciton states in c-AlGaN/GaN asymmetric double quantum wells

Abstract This work presents a theoretical study of the lowest heavy- and light-exciton energy states in a c-AlGaN/GaN asymmetric double quantum well. It makes use of the variational method to determine the eigenstates of the corresponding Schrodinger equation, within the effective mass and parabolic band approximations. We studied the behavior of the exciton energy, the corresponding binding energy as well as the photoluminescence energy peak as a function of the left quantum well width and the central barrier height. Direct and indirect exciton states can be obtained depending on the quantum well configuration. The motivation for this study comes from the experimental reports by T. Wecker et al., in which they measure the photoluminescence energy peak in similar systems with different aluminum concentrations. The comparison of our results with the experimental outputs shows good agreement.