Total Optical Absorption Coefficients Research Articles

Effects of Applied Magnetic Field on the Optical Properties and Binding Energies Spherical GaAs Quantum Dot with Donor Impurity.

The screened modified Kratzer potential (SMKP) model is utilized to scrutinize the impacts of an applied magnetic field (MF) on the binding energies and linear and nonlinear optical properties spherical GaAs quantum dot with donor impurity (DI). To accomplish this goal, we have used the diagonalization method to numerically solve the Schrödinger equation under the effective mass approximation for obtaining the electron energy levels and related electronic wave functions. The expressions used for evaluating linear, third-order nonlinear, and total optical absorption coefficients and relative refractive index changes were previously derived within the compact density matrix method. It has been shown here that the MF and DI impacts the characteristics of the absorption coefficients and the refractive index changes. This study’s results will find application in optoelectronics and related areas.

The impact of hydrostatic pressure and temperature on the binding energy, linear, third-order nonlinear, and total optical absorption coefficients and refractive index changes of a hydrogenic donor impurity confined in GaAs/AlxGa1−xAs double quantum dots

The impact of hydrostatic pressure and temperature on the binding energy, linear, third-order nonlinear, and total optical absorption coefficients and refractive index changes of a hydrogenic donor impurity confined in GaAs/AlxGa1−xAs double quantum dots

Optical absorption in core-shell quantum antidot under applied co-directed electric and magnetic fields

Using the matrix diagonalization method within the effective mass approximation and the rectangular potential profile, we investigate optical absorption coefficients (OAC) in the core-shell quantum antidot (QAD) Al0.3Ga0.7 As/GaAs/Al0.3Ga0.7 As in the presence of applied co-directed electrical and magnetic fields. The electric field effect on the electron wave functions, energy spectrum, oscillator strength of the intersubband electronic transitions is calculated for different size of QAD core and different value of the magnetic field induction. The total, linear and nonlinear optical absorption coefficients in QAD are obtained by considering 1 s-1p and 1p-1d electron quantum transitions as functions of the incident photon energy.

Effects of magnetic, electric, and intense laser fields on the optical properties of AlGaAs/GaAs quantum wells for terahertz photodetectors

We investigate optical absorption coefficients and changes in the refractive index in single- and double-step GaAs/AlGaAs quantum wells under the influence of magnetic, electric, and intense laser fields. For single-step quantum wells, increasing the intensity of the external laser and electric fields induces a red-shift in the total optical absorption coefficient and change in the refractive index and increases their amplitudes; however, increasing the magnetic field generates a blueshift in the optical absorption and change in the refractive index. For double-step quantum wells, the transition energy between the ground and first excited state is strongly decreased. In addition, the total optical absorption coefficients and changes in the refractive index incur a blue shift when the electric and magnetic fields are increased and a red-shift with increasing laser fields. Our analysis of coupling matrix elements, probability densities, and energy levels show that intense laser, electric, and magnetic fields can be harnessed to adjust and tune total optical absorption coefficients and refractive indices for terahertz applications.

Theoretical study of electronic and optical properties in doped quantum structures with Razavy confining potential: effects of external fields

We investigate the energy states of confined electrons in doped quantum structures with Razavy-like confining potentials. The theoretical investigation is performed within the effective mass and parabolic band approximations, including the influence of externally applied electric and magnetic fields. First, we analyze the case of a Razavy quantum well and determine its conduction subband spectrum, focusing on the lowest energy levels and their probability densities. These properties have been numerically determined by self-consistently solving the coupled system of Schrödinger, Poisson, and charge neutrality equations. Doping is introduced via an on-center $$\delta$$ -like layer. In order to evaluate the associated total (linear plus nonlinear) optical absorption coefficient (TOAC), we have calculated the corresponding diagonal and off-diagonal electric dipole matrix elements, the main energy separation, and the occupancy ratio which are the main factors governing the variation in this optical response. A detailed discussion is given about the influence of doping concentration as well as electric and magnetic fields, which can produce shifts in the light absorption signal, toward either lower or higher frequencies. As an extension of the self-consistent method to a two-dimensional problem, the energy states of quantum wire system of circular cross section, with internal doping and Razavy potential, have been calculated. The response of eigenvalues, self-consistent potentials and electron densities is studied with the variation in $$\delta$$ -doping layer width and of the donor density. Finally, the origin of Friedel-like oscillations, that arise in the density profile, generated by the occupation of internal and surface electronic states has been explained.

The effects of temperature and pressure on the optical properties of a donor impurity in [formula omitted] multilayer cylindrical quantum dots

This paper examines the variation of the linear, third-order nonlinear and total intersubband optical absorption (refractive index changes) coefficients of a donor impurity in multilayer cylindrical quantum dots (MCQDs), under the effect of temperature T and hydrostatic pressure P. Moreover, in this study, we also examined the effect of structure parameters on the optical absorption coefficients of the system. The Schrödinger equation describing the system is solved numerically by the finite element method (FEM) within the effective mass approximation. In our calculations, the confinement potential is modeled by a parabolic form in the radial direction and a square one in the z-direction. The optical absorption coefficients and refractive index changes have been investigated versus the quantum dot radius, indium composition and intensity of the incident electromagnetic for three allowed transitions: 1s - 1p, 2s - 1p and 1p - 1d. Our essential outcomes exhibit that the optical absorption coefficients and refractive index changes are strongly sensitive to the variation of quantum dot sizes, which enhance and blueshift as the quantum confinement is strong. On the contrary, the optical absorption coefficients and refractive index changes diminish and redshift as the quantum confinement reduces.

Regulation of optical properties by applied external fields for a quantum well with Hulthen potential

In this present study, the effects of electric, magnetic, and non-resonant intense laser field (ILF) on the linear, third-order nonlinear, and total optical absorption coefficients (TOACs) and relative refractive index changes (RRICs) of GaAs quantum well, having Hulthen confinement potential, were theoretically investigated. In addition, the dependence of the nonlinear optical properties in the structure on the optical intensity of incident photon and the inverse relaxation time was also calculated. To do this research, firstly the energy eigenvalues and eigenfunctions of the structure were calculated by using the effective mass and envelope function approaches. By using these calculated subband energy levels and wave functions belonging to these levels, the nonlinear optical properties of the system were obtained via the iterative method, within the compact density matrix approach framework. The obtained numerical results show that the optical properties of the considered system depend on the externally applied fields. With the applied external electric and magnetic field, the peak positions of TOACs and RRICs shift to higher energies, and the peak magnitudes increase. The high-frequency ILF applied to the structure shifts the peak positions of TOACs and RRICs initially towards higher energies and then towards lower energies and their peak sizes increase. These results show that the optical properties of the system can be adjusted purposively by changing the magnitude of applied external fields.

Terahertz laser field manipulation on the electronic and nonlinear optical properties of laterally-coupled quantum well wires.

An intense terahertz laser field is shown to actively manipulate the electronic states, as well as the linear and nonlinear optical absorption coefficients, of the laterally-coupled quantum well wires (LCQWWs). The laser-dressed quantum states of the LCQWWs are achieved using the non-perturbative Floquet method and the two-dimensional diagonalization technique under the effective mass approximation. We have demonstrated that the intense terahertz laser field induces a strong deformation of the confinement potential configuration of the LCQWWs, thus pronouncedly dressing the energy levels and wave functions. An unambiguous picture is depicted for the evolution of the laser-dressed quantum states with the increase of the laser-dressed parameter characterizing the strength of the laser-dressed effect. On this basis, the resonant peak positions of the linear and nonlinear optical absorption coefficients feature a blue shift followed by a red shift with an increase of the laser-dressed parameter. Furthermore, the evolution of the peak values for the linear and third-order nonlinear optical absorption coefficients as a function of the laser-dressed parameter is comprehensively discussed. Moreover, in contrast to the case without intense terahertz laser field, the peak values of the linear, third-order nonlinear, and total optical absorption coefficients can be obviously enhanced at the same frequency position by manipulating the appropriate laser-dressed parameter. A similar feature can be found in the linear, third-order nonlinear, and total refractive index changes. Our findings are conducive to the implementation of the expected quantum states and nonlinear optical effects in the LCQWWs, paving the way for new designs in tunable optical switches, infrared photo-detectors and infrared modulators.

Numerical Study of Temperature and Electric Field Effects on the Total Optical Absorption Coefficient in the Presence of Optical Inter-Conduction-Subband Transitions in InGaN/GaN Single Parabolic Quantum Wells

In this paper, we theoretically investigate the total optical coefficient (TOAC) considering 1S-2P and 2S-2P conduction subband transitions in a single parabolic quantum well (SPQW) with an on-center hydrogen-like impurity. Within the framework of the effective-mass approximation, the Schrödinger equation is solved numerically to obtain the eigenvalues and their corresponding eigenvectors using the finite difference method. The calculations are performed for finite confinement potential height, taking into account the dielectric and effective mass mismatches between GaN and InGaN materials under the considered electric field and temperature effects. The temperature dependence of the effective mass, dielectric constant and band gap energy are obtained accordingly. On the one hand, the results show that a significant shift is produced with the variation of both the temperature and the intensity of the electric field. On the other hand, the absorption spectrum is shifted to lower energies with increasing both electric field strength and temperature. Moreover, its amplitude is enhanced with an increase in the intensity of the electric field, and show a slight drop with increasing temperature for the two optical transitions considered. The results show that such parameters can be used to adjust the optical properties of single parabolic Quantum Well for solar cell applications.

Linear and Nonlinear Magneto-optical Absorption Coefficients and Refractive Index Changes in Wse2 Monolayer

This work studies the linear, the third-order nonlinear, and the total optical absorption coefficients (OACs) and the refractive index changes (RICs) caused by both intra- and inter-band transitions in the WSe2 monolayer. The expression for the OACs and RICs in the presence of a magnetic field as well as the Zeeman and electric fields are found by using the compact density matrix approach. The results show that the spin states strongly affect the OACs and RICs, which display the violet-shift behavior with the increase of the magnetic field. The Zeeman fields do not affect the peak positions but slightly reduce peak intensities. The OACs and RICs due to intra-band transition display only one peak in the THz range, while the inter-band spectra show a series of peaks in the near-infrared optical range, making monolayer WSe2 be a promising candidate for novel optoelectronic applications.

Effect of magnetic field, size and donor position on the absorption coefficients related a donor within the core/shell/shell quantum dot

In this study, linear, nonlinear and total optical absorption coefficients related a single shallow donor atom confined in semiconductor core/shell/shell quantum dot heterostructure are researched in detail within the compact density matrix formalism approximation. For this purpose, firstly, the energies and the wavefunctions are computed by the diagonalization method in the effective mass approach. Moreover, the effects of size modulation, donor position and magnetic field are analyzed. The numerical results indicate that the linear and nonlinear parts of the absorption coefficients related with intersubband \(1s\rightarrow 1p\) and \(1p\rightarrow 1d\) donor transitions undergo significant changes.

Theoretical analysis of intersubband optical absorption in asymmetric AlInN/GaN/AlInN quantum well heterostructures

The intersubband optical absorption coefficients were theoretically investigated in asymmetric AlInN/GaN/AlInN quantum wells. The electron band parameters are calculated by solving, self-consistently, the one-dimensional Poisson and Schrödinger equations under Hartree and effective mass approximations. The intersubband optical absorption between the two lowest levels was calculated based on the density matrix formalism. The effects of polarization, indium composition and delta-doping on the optical absorption coefficients in AlInN/GaN double heterostructures were studied. Results have revealed: i) an enhancement of the total (linear plus nonlinear) absorption coefficient peak and a reduction of wavelength due to the polarization effects ii) that the peak of the total optical absorption coefficient increased and showed a red shift upon increasing indium composition iii) that the peak of the total absorption coefficient increased and red-shifted or blue-shifted through optimizing the concentration of the planar doping in the AlInN barriers. Furthermore, the use of a back doping with a delta-shaped profile was identified as a consistent approach to carry out the transition 1.55 µm. The results in this study could be useful for the design and applications of optoelectronic devices operating at 1.55 µm.

Donor impurity atom effect on the inter-subband absorption coefficient for symmetric double n-type δ-doped GaAs quantum well

In this work, the electronic structure and the inter-subband absorption coefficient (IAC) are theoretically studied for symmetric double n-type δ-doped GaAs quantum well considering the donor impurity atom effect. The electron states are determined by a diagonalization procedure, working within the effective mass and parabolic band approximations, and the effect of donor center is treated via the variational method. Meanwhile, linear and nonlinear contributions for the inter-subband absorption coefficient were evaluated from expressions usually derived within the perturbative solution of the Von Neumann equation for density matrix. We report the impurity binding energy by considering a donor atom located at the center of the system (at zi = 0). We found that the reported physical properties become more sensitive to the inter-well separation distance Lw than to the δ-doping density, N2d. In the former case the total optical absorption coefficient undergoes an important red-shift as well as a significant decrease in its magnitude. When N2d values increase, the binding energy exhibits a contrary effect, and the total optical absorption coefficient exhibits an small blue-shift with no significant changes in its magnitude. The presence of the donor impurity atom in the system represents one factor that can modify the location of inter-subband absorption coefficient, by inducing a blue-shift of the optical response. The resonant peak energies are within the range of several terahertz, showing potential device applications within this range of the electromagnetic spectrum.

Optical properties of a GaAs quantum well with new type of hyperbolic confinement potential: Effect of structure parameters and intense laser field

In this present study, we have investigated theoretically the effect of structure parameters (η and κ) and high-frequency intense laser field (ILF) on the linear and nonlinear optical properties of a GaAs quantum well (QW) with new type of hyperbolic confinement potential. Within the framework of the effective-mass and parabolic band approximations, we have computed the confined subband energy levels and their corresponding densities of probability by using the diagonalization method. Besides, we evaluated the total optical absorption coefficients (TOACs) and total refractive index changes (TRICs). The obtained numerical findings show that an increase of the η (κ) structure parameter causes an increase (decrease) in amplitude in TOACs and a blue (red) shift of the resonance energy spectrum. In addition, with the increase of the ILF, the resonance energy spectrum shifts to blue, while the amplitude of TOACs (TRICs) increased (decreased). We think that the obtained these results can be useful in the design of new device’s generation employed in optoelectronic domain.

Effects of hydrostatic pressure and temperature on the nonlinear optical properties of semiparabolic plus semi-inverse squared quantum wells* *Project supported by the Natural Science Foundation of China (Grant Nos.11604289, 11804063, and 51971193), the BaGui scholar program of Guangxi Province in China and the Natural Science Foundation of Guangxi in China (Grant No.2016GXNSFBA380017).

In this study, the effects of hydrostatic pressure and temperature on nonlinear optical rectification (OR), second-harmonic generation (SHG), third-harmonic generation (THG) and the linear, nonlinear, and total optical absorption coefficients (OACs) of a semiparabolic plus semi-inverse squared quantum well (QW) are theoretically investigated. The results show that hydrostatic pressure and temperature have significant effects on the optical properties of semiparabolic plus semi-inverse squared QWs, and that the energy levels and magnitudes of the resonant peaks of OR, SHG, THG, and the total OACs vary according to the shape of the limiting potential, the hydrostatic pressure, and the temperature. It is easily seen that the peak positions of the resonant peaks of OR, SHG, THG, and the total OACs in the semiparabolic plus semi-inverse squared QW show a red shift with increasing hydrostatic pressure, but a blue shift with increasing temperature. Therefore, the magnitude and position of the resonant peaks of OR, SHG, THG, and the total OACs can be adjusted by changing the hydrostatic pressure and the temperature, which promise a new degree of freedom in the tunability of various electro-optical devices.

Non-resonant intense laser field effect on the nonlinear optical properties associated to the inter- and intra-band transitions in an anharmonic quantum well submitted to electric and magnetic field

Simultaneous effects of electric, magnetic, and non-resonant intense laser field on the nonlinear optical properties of a GaAs quantum well with an anharmonic confinement potential profile are theoretically investigated. Energy eigenvalues and eigenfunctions of the system are determined using the diagonalization method within the framework of the effective mass and parabolic band approximation. Nonlinear optical properties associated to the inter and intra band transitions are evaluated. Our numerical results for the intra-band response show that the resonance peak positions of the total optical absorption coefficients and relative refractive index changes shift towards higher energy levels (blueshift) by increasing the strength of the applied external electric, magnetic, and non-resonant intense laser field. The analysis of inter-band (electron-heavy hole) transitions reveals that the optical coefficients has a pronounced redshift induced by the electric field while a blueshift is caused by the magnetic and laser signals. It is seen that the nonlinear optical properties of such structures can be adjusted according to the purpose by changing the external perturbations and could be used in new optoelectronic device designs.

The effect of impurity position and doping concentration on the binding energies and total optical absorption coefficients in a $${\delta }$$-doped quantum well

In this present work, for different impurity position and ionized doping concentrations, we have theoretically investigated the linear, third-order nonlinear, and total optical absorption coefficients corresponding to the $$(1\rightarrow 2)$$ intersubband transitions between the ground and first-excited conduction band states in a single $$\delta $$ -doped GaAs well, with and without the presence of a donor impurity. Impurity binding energies were calculated using the effective-mass and parabolic band approximations within a variational scheme. The linear, third-order nonlinear, and total optical absorption coefficients for the intersubband transitions are calculated within the compact density matrix approach. The obtained results show that adding an impurity positioned at the symmetry center of the well, as well as the increase in the ionized donor concentrations, shifts the total optical absorption coefficients to higher photon energies. However, the off-center positions of impurities together with the varying ionized donor concentrations lead to blue or red shifts in relation to the values of binding energies. The results in this study may be useful for the design and applications of the devices based on the $$\delta $$ -doped structures.

Optical properties of spherical quantum dot in the presence of donor impurity under the magnetic field

In this study, the binding energies of an on-center and off-center hydrogenic donor impurity in a spherical quantum dot with finite confinement potential under an applied external magnetic field are investigated in detail by using the matrix diagonalization method in the effective mass approximation. Depending on the calculated energies and wave functions, the linear, third-order nonlinear and total optical absorption coefficients between the ground and several excited states are examined by the iterative method in the compact density matrix approximation for the two-level system. The combined effect of donor position, magnetic field and dot size on binding energies and optical absorption coefficients is observed. The results show that these effects cause significant changes on donor binding energy and optical absorption coefficients.

Effect of intense laser and electric fields on nonlinear optical properties of cylindrical quantum dot with Morse potential

In this study, the influence of the external electric field on the nonlinear optical properties of a laser dressed cylindrical quantum dot with axial Morse potential are theoretically investigated using the total optical absorption coefficient as well as relative refractive index changes. The effect of the structural parameters on the structure's intraband optical properties is analyzed, optimizing the quantum dot in terms of the total optical absorption coefficient and the relative refractive index. Single-electron energies and wave functions of the system have been determined using analytical methods and the exact diagonalization technique. The quantities above mentioned are examined with the compact-density-matrix approach. The obtained results demonstrated that the system's intraband optical properties closely depend on both the applied external fields and the structural parameters. Such adequate tuning of the laser-dressed cylindrical quantum dots’ intraband optical properties gives us new possibilities in the regions of interest for optoelectronic device applications.

Theoretical investigation of linear and nonlinear optical properties in an heterostructure based on triple parabolic barriers: Effects of external fields

In this work, we have investigated theoretically the impact of intense laser, electric and magnetic fields on the linear and nonlinear optical properties of a quantum well heterostructure containing triple parabolic barriers (GaAs/AlGaAs). Within the framework of the effective-mass and parabolic band approximations, we have computed the confined lowest energy levels and their corresponding densities of probability, through the use of a finite difference technique to solve the corresponding differential equation. Besides, we evaluate the total optical absorption (TOACs) and relative refractive index change (RRICs) coefficients. The obtained findings show that an increase of the intensity of the intense laser field produces a blue shift at first and then a red shift of the TOACs and RRICs. A specific value of the laser field separating the two kinds of signal displacements is outlined. Contrarily to the intense laser field, an increment of the external static electric and magnetic fields induces only a blue shift in the variation of the TOACs and RRICs. In addition, we have discussed in detail the variation of diagonal and non-diagonal matrix elements which are responsible on the variation of the amplitudes of the TOACs and RRICs. We think that the obtained results can be useful in the design of new device's generation employed in optoelectronic domain.