Asymmetric Triple Quantum Well Research Articles

Nonlinear optical properties of GaAs/AlGaAs asymmetric triple quantum wells designed for quantum cascade lasers: Effect of externally applied electric and magnetic fields

We explore the impact of external fields on the absorption coefficients and relative refractive index changes in a quantum cascade laser profile-like heterostructure that consists of a triple asymmetric quantum well. Firstly, we solve numerically the time-independent Schrödinger equation by using the diagonalization method under the effective mass and parabolic band approaches, to obtain the energy levels and wavefunctions. Then, we evaluate the optical coefficients from the analytical expressions derived from the compact density matrix method. The obtained results put forth that the resonant peaks of optical coefficients shift to higher (lower) energies by increasing the value of the electric (magnetic) field. These results indicate that it would be possible to adjust the optical properties of these structures to the desired range with external fields. As a result, we hope that new optoelectronic devices based on asymmetric triple quantum wells can be developed using the features found here.

Influence of hydrostatic pressure and temperature on the optical responses of asymmetric triple quantum wells

Influence of hydrostatic pressure and temperature on the optical responses of asymmetric triple quantum wells

Effects of external electric and magnetic field on the nonlinear optical rectification, second, and third-harmonic generations in GaAs/AlGaAs asymmetric triple quantum well

Effects of external electric and magnetic field on the nonlinear optical rectification, second, and third-harmonic generations in GaAs/AlGaAs asymmetric triple quantum well

The third-order nonlinear optical susceptibility of Al$$_{x}$$Ga$$_{1-x}$$As/GaAs asymmetric triple quantum wells

The third-order nonlinear optical susceptibility of Al$$_{x}$$Ga$$_{1-x}$$As/GaAs asymmetric triple quantum wells

Electronic characteristics of asymmetric triple GaAlAs/GaAs and GaInAs/GaAs quantum wells depending on Al and In concentration

Herein, the electronic characteristics of asymmetric triple Ga1-x Alx As/GaAs quantum wells (A model) and Ga1-x Inx As/GaAs quantum wells (B model) have been examined as dependent on Al and In concentration. The energy levels, the wave functions and the finding probability of electron in quantum well (QW) of these systems under effective mass approach were concluded by Schrödinger equation solution. According to our results, the main differences between models A and B are effective mass and energy gap. For A model, GaAlAs is the barrier and GaAs is the well. Whereas for B model, GaAs is the barrier and GaInAs is the well. Also, the energy levels and the potential height of B model are unceasingly higher than of B model. The concentration ratio has a great impact on the electronic features of the asymmetric triple quantum well (ATQW). These features have a convenient attention for the purpose of adjustable semiconductor devices.

Parity-time symmetry and asymmetric diffraction of light in four-level triple quantum wells

In this paper, we investigate two-dimensional parity-time (PT) symmetry and electromagnetically induced grating (EIG) in four-level asymmetric triple quantum wells (QWs). Here, PT-symmetry and EIG are realized by appropriately varying the detuning value of the probe, and the modulation amplitudes of a coupling field and standing wave (SW) pump. By virtue of its PT symmetry, the EIG asymmetrically diffracts the probe beam. The angular switching of the diffracted beam can be achieved either by varying the probe or the coupling and SW pump fields. The intensity distribution of the diffracted beam over higher-order diffraction peaks depends on the interaction length in the QW. For small interaction lengths, most of the energy is distributed close to the central diffraction peak. With an increase in the interaction length, energy is gradually transferred to higher order diffraction peaks.

Photoluminescence properties of epitaxial asymmetric triple CdSe quantum wells

The authors present the results of the photoluminescence characterization of three asymmetric triple quantum well (ATQW) systems. Each one contains three ultrathin CdSe quantum wells of 1, 2, and 3 monolayers (ML) thickness grown by atomic layer epitaxy between ZnSe separating barriers. Two systems have coupled QWs due to thin 5 nm thick ZnSe separating barriers, and the uncoupled system has 100 nm ZnSe separating barriers. Two of them (5 and 100 nm ZnSe barriers) were grown in the sequence 3–2–1, with the 3 ML QW closer to the substrate, while the third ATQW (5 nm ZnSe barrier) was grown in the reverse order. The photoluminescence spectrum of the uncoupled ATQW (3–2–1 sequence) presents three excitonic peaks, one peak for each QW, with the same emission energies of corresponding isolated single QWs. In the case of two coupled ATQW systems (3–2–1 and 1–2–3 growth sequence), the authors observed only one peak, corresponding to the lowest transition energy in the system formed by the three coupled QWs. The calculation of the wavefunctions shows no overlap for 100 nm ZnSe separating barriers, as expected for this thick barrier. For the systems with 5 nm ZnSe barriers, the calculations indicate that the overlap occurs mainly between the wavefunctions of the central 2 ML thick CdSe QW and the neighboring 1 ML and 3 ML QW wavefunctions; the overlap between the 1 and 3 ML QWs is small as a consequence of their 10 nm separation. The authors found that the effect of the coupling between the QWs is more easily identified by the reduction (or absence) of the intensity of the higher energy transitions of the multiple QW system than by the change of the ATQW energy levels with barrier thickness reduction.

Dependence on well widths of total optical absorption coefficient of asymmetric triple GaAlAs/GaAs and GaInAs/GaAs quantum wells

Herein, the total optical absorption coefficient (TOAC) and the electronic characteristics of asymmetric triple Ga[Formula: see text]Al[Formula: see text]As/GaAs (A model) and Ga[Formula: see text]In[Formula: see text]As/GaAs (B model) quantum wells (QWs) have been examined related to the well widths (WWs). For TOAC, we first varied all WWs equally, and then we kept a WW constant and changed the other two WWs. The wavefunctions (WFs), the subband energies and the probability densities of asymmetric triple quantum wells (ATQW) with different QW shapes under effective mass approach were determined by the solution of Schrödinger equation. According to the results obtained, the major diversities of A and B models are the effective mass and the energy gap. The potential depth and the energy levels (ELs) of A model are continuously smaller than of B model. We see that WWs have a great influence on TOAC and the electronic features of ATQW. The inter-subband absorption spectrum designates blue/red shifts, when the energy spacing varies with WWs. These characteristics draw a convenient attention for the purpose of adjustable semiconductor devices. Hence, the alteration of this absorption spectrum, which could be fit for many optical modulators and infra-red optical device applications, may be efficiently realized by changing WWs. Highlights Energy spacing varies by increasing WWs. Due to the shape of the wells, the influence of each WW is quite different from the others. TOAC varies with rising WWs. The absorption spectrum illustrates red or blue shifts depending on WWs.

Linear and nonlinear optical properties of asymmetric triple quantum wells under intense laser field

For asymmetric triple quantum wells (ATQW) the linear and nonlinear optical absorption coefficient (OAC) and the optical refractive index change (ORIC) are analyzed according to the intense laser field (ILF). The obtained results show that the ILF parameter () has an important effect on the shape and height of the confined potential profile of the ATQW, and alterations in the energy levels and the dipole moment matrix elements depend on the shape of the confinement potential. For = 10 nm (according to the parameters used in this study), ATQW turns into an asymmetric wider double confinement potential. As a consequence of the energy difference between the energy states, the absorption spectrum of (1–2) and (1–3) optical transitions initially shows a redshift (up to = 6 nm and = 4 nm, respectively) and then indicates a blueshift by increasing the ILF. For the (2–3) transition, the optical absorption spectrum continuously shows a blueshift and displays an oncoming shift toward the higher energies. Thus, the linear and nonlinear OAC and ORIC may be adjusted by modifying the ILF parameter. Our results are of use in the investigation into new ways of manipulating the optoelectronic properties of triple quantum well devices.Highlights• The electronic and optical properties of ATQW vary with increasing ILF value.• The effect of ILF on the quantum well (QW) differs depending on the shape of the QW.• OAC and ORIC change with rising ILF.• The absorption spectrum shows blueshifts or redshifts depending on the ILF.

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.

Interband transitions dependent on indium concentration in Ga1−xInxAs/GaAs asymmetric triple quantum wells

In this paper, the optical and electronic properties of asymmetric triple quantum well (ATQW) structures are studied depending on the indium concentrations while quantum well (QW) thicknesses and barrier widths are kept constant. Calculation of electronic properties are done within the framework of the effective mass approximation. The indium concentrations in left quantum well (LQW) and right quantum well (RQW) are varied in order to see the change of energy levels. Then, interband transition energies, wavelengths, oscillator strengths and radiative decay times are determined depending on barrier height. The scope of this study, for the first time in the literature, covers converged interband transition energies for the asymmetric quantum well structures.

Two narrow dark polaritons in triple-well microcavity based on double tunneling induced transparency

In this paper, we propose and demonstrate that two dark polaritons can be generated in a microcavity that several periods of asymmetric triple-quantum wells are embedded in. They are created by the intracavity coherent effects based on tunneling induced transparency and can be switched by using an external laser. The group time delay of this system is calculated to show the slow dark polaritons. The results have potential applications in all-optical switching and buffering in nano-scale.

Light propagation in a coupled waveguide‐triple quantum well structure

AbstractThe light propagation in a waveguide which was weakly coupled to a quantum well (QW) structure was studied to demonstrate the detectability of the electronic states in the small area of QW. The small area of QW was made with a GaAs/AlGaAs asymmetric triple QW. Since the electronic states in the triple QW were easily controlled by an electric field which was induced by an optical injection, we observed the optical spectra obtained from the waveguide under the various intensities of optical injection. The spectral change was observed around the characteristic wavelengths of the QW. In order to verify the observed spectral change, we measured the optical spectra of the traveling wave in a sample whose QW surface has been etched off. By comparing the results, we interpreted that the spectral change is due to the reconstruction of the electronic states in the small area of QW due to the optically excited carriers. This proves the detection of small electronic state changes in the small area of QW with the traveling light in the waveguide. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Mixing/Resonance of Electronic States and Optical Nonlinearity in a GaAs/AlGaAs Asymmetric Triple Quantum Well Structure

The input power dependence on the transmission of a light through a GaAs/AlGaAs asymmetric triple quantum well (ATQW) shows strong nonlinearity at 77 K, the behavior of which depends on the wavelength of the input light. By studying the relation of nonlinearity to the photoluminescence spectra, the resulting phenomenon is attributed to the Stark shift and change of the optical oscillator strength which is due to the triple resonance of the electronic states. The triple resonance is induced by the temporal separation of photo-excited electrons and holes.

Valence-band mixing effects on exciton dipole terahertz emission from asymmetric triple quantum wells

We analyze the influence of band mixing on the dynamics of hole tunneling in asymmetric GaAs–Ga1−xAlxAs triple quantum wells. A combination of the time-dependent Schrödinger equation and the Luttinger Hamiltonian is used to calculate the terahertz radiation from excitons. When the electric field required for resonance of electrons between the central and right well coincides with the field needed for hole resonance between the central and left well the radiation is strongly increased. If this field coincides with the hole mixing field at k∥≠0, a new modulation of the dipole emission appears, being drastically affected in frequency and amplitude. The calculated effect is greater than previous results for asymmetric double quantum wells.

Terahertz emission with a time-dependent amplitude in asymmetric triple quantum wells

In this work, we have numerically integrated in space and time the effective-mass Schrödinger equation for an exciton in a GaAs/GaAlAs triple quantum well heterostructure. Considering a Coulomb interaction between the electron-hole pair in a triple quantum well, we have obtained a time-varying dipole moment in the system whose amplitude is also oscillating with time. In this way, we have shown the possibility of having a new kind of terahertz electromagnetic radiation emerging from a semiconductor device after an optical excitation of the system.