Optical Properties Of Quantum Wells Research Articles

Simultaneous effects of the position dependent mass and magnetic field on quantum well with the improved Tietz potential

In this study, we explored the synergistic impact of position-dependent mass and magnetic field on the electronic and optical properties of quantum wells, featuring an enhanced Tietz potential confinement incorporating both standard Morse and improved Rosen–Morse potentials, as influenced by variations in the structural parameter. Calculations were conducted within the framework of effective mass and parabolic band approximations. The diagonalization method was employed, selecting a wave function basis of trigonometric orthonormal functions to determine the eigenvalues and eigenfunctions of the confined electron potential. Our findings reveal that alterations in the sizes and shapes of the quantum wells, magnetic field strength, geometric asymmetry, and confinement parameters lead to significant variations in electron energies, transition between electron states, and the absorption spectrum. These outcomes offer valuable insights for investigating the electronic and structural properties of materials and devising novel materials with tailored optical characteristics.

Electronic and optical properties of the exponential and hyperbolic Rosen–Morse types quantum wells under applied magnetic field

In this study, we considered the electronic and optical properties of quantum wells with the exponential and hyperbolic Rosen–Morse potentials under an applied magnetic field. Calculations are made within the framework of effective mass and parabolic band approximations. We have used the diagonalization method by choosing a wave function based on the trigonometric orthonormal function to find eigenvalues and eigenfunctions of the confined electron. Our results show that the magnetic field, asymmetry, and confinement parameters cause a significant increase in electron energies and energy differences between the electron states and the blue shift in the absorption peaks. These results can be used to probe materials’ electronic and structural properties and develop new materials with tailored optical properties.

Position-Dependent Effective Mass and Asymmetry Effects on the Electronic and Optical Properties of Quantum Wells with Improved Rosen–Morse Potential

In this study, we investigated, for the first time, the effects of the spatially varying effective mass, asymmetry parameter, and well width on the electronic and optical properties of a quantum well which has an improved Rosen–Morse potential. Calculations were made within the framework of the effective mass and parabolic band approximations. We have used the diagonalization method by choosing a wave function based on the trigonometric orthonormal functions to find eigenvalues and eigenfunctions of the electron confined within the improved Rosen–Morse potential. Our results show that the position dependence mass, asymmetry, and confinement parameters cause significant changes in the electronic and optical properties of the structure we focus on since these effects create a significant increase in electron energies and a blue shift in the absorption spectrum. The increase in energy levels enables the development of optoelectronic devices that can operate at wider wavelengths and absorb higher-energy photons. Through an appropriate choice of parameters, the Rosen–Morse potential offers, among many advantages, the possibility of simulating heterostructures close to surfaces exposed to air or vacuum, thus giving the possibility of substantially enriching the allowed optical transitions given the breaking of the system´s symmetries. Similarly, the one-dimensional Rosen–Morse potential model proposed here can be extended to one- and zero-dimensional structures such as core/shell quantum well wires and quantum dots. This offers potential advancements in fields such as optical communication, imaging technology, and solar cells.

Determination of optical properties of quantum wells with a structure of AlGaN/GaN resonant tunneling diodes (RTDs)

Two-dimensional multiple quantum well (MQW) and modified symmetric quantum well (MSQW) carrier confinement play an important role in AlGaN/GaN resonant tunneling diodes (RTDs) efficiency improvement. Therefore, AlGaN-based materials are suitable for development of ultraviolet-light sources. Hence, an attempt is made to investigate the optical properties of AlGaN/GaN. Asymmetric quantum well structure consisting of N-doped AlGaN wells, GaN steps, and undoped AlGaAs barriers is developed. The significant absorption is observed due to the strong coupling effect of the electronic state wave functions. Asymmetric potential well proposed for AlGaN/GaN/AlGaN RTDs. The barriers and the thin layer in the quantum well are theoretically determined. For GaN/AlGaN QW of width L, the frequencies of the symmetric interface modes satisfy the condition. The increase in well width increases the full-width at half maxima (FWHM) from 0 to 100 nm, while increased Al concentration decreases FWHM from 6 to 1 nm.

Effect of Substrate Misorientation on the Structural and Optical Characteristics of In-Rich InGaAs/GaAsP Quantum Wells

InGaAs quantum well (QW) lasers have attracted significant attention owing to their considerable potential for applications in optical communications; however, the relationship between the misorientation of the substrates used to grow InGaAs QWs and the structural and optical properties of QWs is still ambiguous. In this study, In-rich InGaAs/GaAsP single QWs were grown in the same run via metal organic chemical vapor deposition on GaAs (001) substrates misoriented by 0°, 2°, and 15° toward (111). The effects of substrate misorientation on the crystal quality and structural properties of InGaAs/GaAsP were investigated by X-ray diffraction and Raman spectroscopy. The 0° substrate exhibited the least lattice relaxation, and with increasing misorientation, the degree of lattice relaxation increased. The optical properties of the InGaAs/GaAsP QWs were investigated using temperature-dependent photoluminescence. An abnormal S-shaped variation of the peak energy and inverse evolution of the spectral bandwidth were observed at low temperatures for the 2° substrate, caused by the localization potentials due to the In-rich clusters. Surface morphology observations revealed that the growth mode varied with different miscuts. Based on the experimental results obtained in this study, a mechanism elucidating the effect of substrate miscuts on the structural and optical properties of QWs was proposed and verified.

Lattice relaxation in semipolar AlxGa1−xN grown on (11̅02) AlN substrates

Semipolar AlxGaN films (∼660 nm thick) are fabricated on (11̅02) (r-plane) AlN substrates. X-ray diffraction measurements suggest that the structural quality is relatively good although lattice relaxation occurs. The experimentally evaluated relaxation degrees are 0.90 and 0.72 along the [11̅01̅] and [112̅0] directions, respectively. These values, which are much larger than those of c-plane AlxGaN for a similar Al composition and thickness, are reproduced by a calculation. Dislocations due to lattice relaxation are confined to the vicinity of the AlxGaN/AlN interface, suggesting a small effect on the optical properties of quantum wells fabricated on r-plane AlxGaN/AlN templates.

Nonlinear optical properties of triple δ-doped quantum wells: The impact of the applied external fields

In the present paper, we theoretically investigate the effect of applied external fields, such as electric, magnetic, and intense terahertz laser fields on the optical absorption and the relative refractive index change coefficients of triple δ-doped quantum well structures. To investigate the applied external field effects, we perform the calculation of the allowed subband energy levels and their corresponding eigen-functions using the diagonalization method within the framework of the effective-mass approximation. The effects of the applied external fields on the nonlinear optical properties of the quantum well structure are treated within the compact-density-matrix approach via the iterative method. The numerical results obtained are presented for two different values of electric, magnetic, and intense terahertz laser fields. These results show that changing the intensity of the external electric, magnetic, and intense terahertz laser field. It is concluded that the nonlinear optical response of the triple δ-doped structure can be significantly changed through the changes in the configuration of the external probes.

The role of temperature ramp-up time before barrier layer growth in optical and structural properties of InGaN/GaN multi-quantum wells

In InGaN/GaN multi-quantum wells (MQWs), a low temperature cap (LT-cap) layer is grown between the InGaN well layer and low temperature GaN barrier layer. During the growth, a temperature ramp-up and ramp-down process is added between LT-cap and barrier layer growth. The effect of temperature ramp-up time duration on structural and optical properties of quantum wells is studied. It is found that as the ramp-up time increases, the Indium floating layer on the top of the well layer can be diminished effectively, leading to a better interface quality between well and barrier layers, and the carrier localization effect is enhanced, thereby the internal quantum efficiency (IQE) of QWs increases surprisingly. However, if the ramp-up time is too long, the carrier localization effect is weaker, which may increase the probabilities of carriers to meet with nonradiative recombination centers. Meanwhile, more nonradiative recombination centers will be introduced into well layers due to the indium evaporation. Both of them will lead to a reduction of internal quantum efficiency (IQE) of MQWs.

Effects of spatial confinement and layer disorder in photoluminescence of GaAs1−xBix/GaAs heterostructures

The structural and optical properties of a set of high-quality GaAs1−xBix/GaAs quantum well (QW) heterostructures with Bi concentrations ranging from 3.5% to 6.7% are studied. The energies of the excitonic ground state transitions are determined as a function of Bi concentration and spatial confinement. The influence of material disorder on the optical properties of QWs is investigated. It is determined that trap-related luminescence responds differently to temperature changes depending on whether the Bi concentration is more or less than 5%. Below 5% it contributes significantly to the overall photoluminescence line shape whereas above 5%, it is insignificant.

Heterointerface effects on the nonlinear optical rectification in a laser-dressed graded quantum well

An investigation of the laser radiation effects on the nonlinear optical rectification in an AlGaAs inverse parabolic quantum well with asymmetrical barriers is performed within the effective mass approximation, taking into account the dielectric mismatch between the semiconductor and the surrounding medium. Using the accurate dressing effect for the confinement potential and electrostatic self-energy due to the image-charges, we prove that: (i) a spatially dependent effective mass in the laser-dressing parameter definition is required for precise calculations of the energy levels; (ii) the dielectric confinement provides a potential mechanism for controlling electronic states and optical properties of quantum wells. In addition, the laser dependence of the energy where the optical rectification reaches its maximum can be adjusted by external electric fields. The joint action of the intense high-frequency laser and static electric fields may provide tuning of the nonlinear properties in this type of dielectrically modulated heterostructures.

Electronic and optical properties of quantum wells embedded in wrinkled nanomembranes

The authors theoretically investigate quantum confinement and transition energies in quantum wells (QWs) asymmetrically positioned in wrinkled nanomembranes. Calculations reveal that the wrinkle profile induces both blue- and redshifts, depending on the lateral position of the QW probed. Relevant radiative transitions include the ground state of the electron (hole) and excited states of the hole (electron). Energy shifts as well as stretchability of the structure are studied as a function of wrinkle amplitude and period. Large tunable bandwidths of up to 70 nm are predicted for highly asymmetric, wrinkled QWs.

Assessing the capabilities and limitations of cathodoluminescence microscopy to investigate the optical properties of individual nanostructures

AbstractUnderstanding the optical properties of individual semiconductor nanostructures is an important step in enabling novel optoelectronic components. The capabilities and limitations of cathodoluminescence microscopy in the scanning and scanning transmission electron microscope in correlating the physical and optical properties of quantum wells, wires and dots is evaluated. In particular the importance of specimen‐electron beam interactions and experimental conditions in maximising spatial resolution are discussed (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Luminescence studies on nitride quaternary alloys double quantum wells

We present theoretical photoluminescence (PL) spectra of undoped and p-doped Al x In 1− x− y Ga y N/Al X In 1− X− Y Ga Y N double quantum wells (DQWs). The calculations were performed within the k.p method by means of solving a full eight-band Kane Hamiltonian together with the Poisson equation in a plane wave representation, including exchange–correlation effects within the local density approximation. Strain effects due to the lattice mismatch are also taken into account. We show the calculated PL spectra, analyzing the blue and red-shifts in energy as one varies the spike and the well widths, as well as the acceptor doping concentration. We found a transition between a regime of isolated quantum wells and that of interacting DQWs. Since there are few studies of optical properties of quantum wells based on nitride quaternary alloys, the results reported here will provide guidelines for the interpretation of forthcoming experiments.

Growth and surface passivation of near-surface InGaAs quantum wells on GaAs (1 1 0)

The growth and surface passivation of near-surface InGaAs quantum wells (QWs) on GaAs (1 1 0) substrate have been investigated. Triangular shaped small islands, approximate areal density of 10 7 cm - 2 , are observed on metal organic vapor phase epitaxially grown GaAs single layer and InGaAs multi-quantum wells (MQWs) surfaces in a wide range of growth temperatures. By optimizing the growth conditions, high quality In 0.22 Ga 0.78 As QWs with optical properties comparable to the same structure grown on GaAs (1 0 0) are obtained. Near-surface single QWs are used to study the surface passivation. Epitaxially in situ grown mono-layer thick GaP and InP layers as well as surface phosphorization with tertiarybutylphosphine (TBP) are utilized as passivation methods. Passivation significantly increases photoluminescence (PL) intensity and carrier lifetime of near-surface QWs. The best passivation efficiency is obtained by surface phosphorization with TBP on (1 1 0)-oriented near-surface QW while the ultra-thin InP layer is the best on (1 0 0)-oriented near-surface QW. After 7 months of air exposure, all passivated near-surface QWs still show high PL intensity comparable to deep QW while the PL intensity of unpassivated samples degraded severely. Also, the differences between the optical properties of QWs on GaAs (1 1 0) and (1 0 0) substrates are observed and discussed.

Magneto‐optics of modulation doped quantum wells based on II–VI semiconductor compounds

AbstractWe review on optical studies of exciton‐electron interaction in modulation doped quantum wells (QWs) based on ZnSe and CdTe semiconductor compounds. The optical properties of QWs containing diluted two‐dimensional electron gases (2DEGs) are well described in terms of charged excitons (trions). Their parameters such as oscillator strength, binding energy, and fine structure are considered in details. In case of moderate densities of 2DEGs, when the Fermi energy falls between the trion and exciton binding energies, the optical properties can be understood in terms of combined exciton‐electron excitations. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Calculations of optical properties in p-doped nitrides quaternary alloys multiple quantum wells

We present theoretical photoluminescence (PL) and absorption spectra of p-doped InGaN/AlInGaN and AlInGaN/InGaN multiple quantum wells (MQWs). The calculations were performed within the k.p method by means of solving a full eight-band Kane Hamiltonian together with the Poisson equation in a plane wave representation, including exchange–correlation effects within the local density approximation. Strain effects due to the lattice mismatch and an internal electric field are also taken into account. We show that by changing the In and Al composition we can reach short and long emission wavelengths. The trends in the calculated Stokes shift, due to many-body effects within the quasi-two-dimensional hole gas (2DHG), are analyzed as a function of the acceptor doping concentration. Since the studies of optical properties of quantum wells based on nitrides quaternary alloys are at an early stage, the results reported here will provide guidelines for the interpretation of forthcoming experiments.

Nonlinear optical properties of a Pöschl-Teller quantum well

The nonlinear optical properties of quantum wells (QWs) represented by a P\"oschl-Teller confining potential are studied. This potential is well suited for such purposes as it can easily become asymmetrical by a correct choice of its parameter set. We calculate the linear and the third-order nonlinear optical intersubband absorption coefficients, the second-harmonic generation (SHG) susceptibility tensor, and optical rectification (OR) under the density matrix formalism. Numerical results for a typical GaAs QW are presented. The resulting SHG and the OR coefficients are much larger than their values for bulk GaAs.

The influence of surface segregation on the optical properties of quantum wells

Segregation of column III atoms during molecular beam epitaxy of III-V semiconductor compounds result in nonabrupt interfaces and surface compositions different from the bulk. This effect modifies the electronic states in the quantum well and the emission energy in the photoluminescence spectrum. In this work, we have solved analytically the Schrödinger equation taking into account the shape changes in the quantum well due to the segregation of atoms during the growth process of the semiconductor heterostructures. We apply this model to the case of indium segregation in the InGaAs/GaAs system. The transition energy calculations between the confined electron and hole states as function of the well width for different In composition and growth temperature are in agreement with the measured photoluminescence energy peaks.

Influence of level filling on optical properties of quantum well

In a specially designed three barrier double well tunneling structure, elect ron injecting from the emitter in combination with escaping through a resonant tunneling structure were used to adjust and control the filling of electrons in different subbands. It was observed that the occupation in the first excited electron state can result in a suppression to quantum confinement Stark effect. Mo reover, at very low bias, a series of intrigue photoluminescence peaks appeared as a small quantity of excess electron was filled in the ground state of the qua ntum well, that cannot be explained by the theory of band to band transition in the framework of single electron picture.

Quantum-well optical modulator at terahertz frequencies

We predict that strong modulation of the optical properties of quantum wells at terahertz frequencies is possible. In this regime, the coherent nonlinear mixing of the optical and the terahertz-modulation fields leads to strong modification of the frequency dependence of the modulation depth.