Nonlinear Intersubband Optical Absorption Coefficients Research Articles

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.

Intersubband transitions in spherical quantum dot quantum well nanoparticle

In this paper, we present results about electronic spectra and optical properties of one-electron spherical quantum dot-quantum well (QDQW) structure. Investigated structure consists of CdSe core surrounded by ZnS shell and caped by infinitely high electron potential barrier which can be a good model for any high enough potential barriers. This specific QDQW structure is determined by CdSe and ZnS properties (effective masses and conductive band offset) and the core size and the shell thickness. We present calculation results for one-electron ground (1s) state and the first excited (1p) state transition. For this transition we have calculated oscillator strengths and linear and third-order nonlinear intersubband optical absorption coefficients for various core and shell size i.e. different CdSe core radii and ZnS barrier thickness. Change in core and shell dimensions induces change in one-electron wave function i.e. electron energy states and localization for both 1s and 1p states. As a result, intersubband 1s–1p transition of this system is greatly dependent on the core and shell size. For very small core radii, less than 0.7 nm, and core radii over 1.5 nm the most probable intersubband transition is 1s–1p, but in the region between 0.7 and 1.5 nm core radii, transitions from 1s to other p states dominates. Investigated properties depend mostly on the core radius. These results connect the dot structure and the optical properties of this particular structure. This behavior is than an illustration of similar systems.

Effect of Conduction Band Non-Parabolicity on the Nonlinear Optical Properties in GaAs/Ga1-xAlxAs Double Semi-V-shaped Quantum Wells.

In this paper, we investigate the effect of conduction band non-parabolicity (NPBE) on the third harmonic generation(THG), the linear and nonlinear intersub-band optical absorption coefficients (OACs) related with electronic states of double semi-V-shaped GaAs/Ga1−xAlxAs quantum wells(QWs) by using the compact-density-matrix approach. Simultaneously, the work is performed in the position dependent effective mass in order to compute the electronic structure for the system by the finite difference and self-consistent techniques. We also compare the results with and without considering NPBE. It is found that: (1) the NPBE has a significant influence on the sub-band energy levels of double semi-V-shaped QWs, and (2) the amplitude and position of the resonant peaks of the THG and nonlinear OACs in the case of considering NPBE show complicated behavior due to the energy dependent effective mass m*(E) where the energy value was chosen self-consistently.

Optical absorption via intersubband transition of electrons in GaAs/AlxGa1−xAs multi-quantum wells in an electric field * * Project supported by the National Natural Science Foundation of China (No. 61764012).

Based on the effective mass approximation, the Schrödinger equation and Poisson equation in GaAs/ AlxGa1−xAs multi-quantum wells (MQWs) are self-consistently solved to obtain the wave functions and energy levels of electrons in the conduction band for the ground first excited state by considering a lateral electric field (LEF). Then, the effects of size, ternary mixed crystal, doping concentration, and temperature on linear and nonlinear intersubband optical absorption coefficients (IOACs), and refractive index changes (RICs) due to the transition between ground states and the first excited states of electrons are discussed based on Fermi’s golden rule. The results show that, under a fixed LEF, with increase of Al composition and doping concentration, the IOACs produce a red shift. With increases of both widths of the wells and barriers IOACs appear as blue shifts and their amplitudes increase, but the barrier width change is much more important to affect nonlinear IOACs, whereas increasing the temperature results in a blue shift first and then a red shift of IOACs. When the other parameters are fixed but there is an increase in the LEF, IOACs occur with a blue shift, and the RICs have similar properties.

Theoretical study of optical absorption in nonpolar AlGaN/GaN step quantum well structures

The linear and nonlinear intersubband optical absorption coefficients (OACs) of nonpolar AlGaN/GaN step quantum well structures (SQWs) were calculated theoretically for various geometrical structures, $$ \delta $$ doping schemes, and material compositions. The results revealed that the absorption frequency of such structures is obviously tunable by changing parameters such as the quantum well width, step barrier width, Al composition in the step barrier layer, and doping position. These characteristics can be attributed to non-polarization-related effects. The doping and Al composition were found to have remarkable effects on the position and magnitude of the peaks in the nonlinear optical absorption spectrum, whereas the geometric parameters of the SQWs, such as the well width and step barrier width, changed the magnitude of the peaks only very slightly. On the other hand, the nonlinear OACs of the SQWs were found to be strongly sensitive to the Al composition x and doping density in the step barrier layer. This study suggests that the step barrier layer in SQWs plays an important role in manipulating their intersubband optical absorption.

Nonlinear optical properties of asymmetric double-graded quantum wells

ABSTRACTIn this work, the effects of the structure parameters, such as the central barrier thickness and the aluminium concentrations x, on the linear and nonlinear intersubband optical absorption coefficients and refractive index changes of the asymmetric double-graded quantum wells (ADGQWs) under the presence of an external static electric field are studied theoretically. The nonlinear optical properties of the ADGQWs are obtained using the compact-density matrix approach and iterative method. The numerical results obtained from the present work show that the external static electric field and the structure parameters play an important role in the optical properties of ADGQWs. Depending on the asymmetric nature of the confinement potential, in an electric field of kV/cm, the overlap between electronic wave functions decreases with increasing field whereas it increases for larger field values. The tunability of intersubband transitions can be applied to optical modulators and various device applications based on the optical transitions of electrons.

Donor-impurity-related optical absorption and refractive index changes in GaAs/AlGaAs core/shell spherical quantum dots

In this study, the linear and nonlinear intersubband optical absorption coefficients (OACs) and refractive index changes (RICs) in GaAs/AlGaAs core/shell spherical quantum dots (QDs) are theoretically investigated within the framework of the compact-density-matrix approach and iterative method for both cases with and without on-center impurity. The energy eigenvalues and their corresponding eigenfunctions of the system are calculated by using the differential method. Our results show that the position and the magnitude of the resonant peaks of the nonlinear OACs and RICs depend strongly on the hydrogenic impurity and QDs radius. It was found that the total OACs indicates saturation at sufficiently high incident intensities. Also we found that the binding energy of the ground and excited states of the impurity depend on the QDs radius.

Nonlinear intersubband transitions in asymmetric double quantum wells as dependent on intense laser field

In this study, for asymmetric double quantum well (ADQW) the linear and nonlinear intersubband optical absorption coefficients and the refractive index changes are examined as dependent on the intense laser field (ILF). The obtained results display that the location and the size of all absorption coefficients and refractive index change depend on ILF and the asymmetric parameter. Also, I showed that ILF provides an important effect on the electronic and optical properties of ADQW, and the changes of the energy levels and the dipole moment matrix elements are dependent on the shape of the confinement potential. Such effects can supply methods to drive tunable semiconductor lasers, which may be tailored by quantum potential well parameters and ILF values.

The effect of hydrostatic pressure, temperature and magnetic field on the nonlinear optical properties of asymmetrical Gaussian potential quantum wells

In this study, simultaneous effects of hydrostatic pressure, temperature and magnetic field on the linear and nonlinear intersubband optical absorption coefficients (OACs) and refractive index changes (RICs) in asymmetrical Gaussian potential quantum wells (QWs) are theoretically investigated within the framework of the compact-density-matrix approach and iterative method. The energy eigenvalues and their corresponding eigenfunctions of the system are calculated with the differential method. Our results show that the position and the magnitude of the resonant peaks of the nonlinear OACs and RICs depend strongly on the hydrostatic pressure, temperature and external magnetic field. This gives a new degree of freedom in various device applications based on the intersubband transitions of electrons.

Linear and nonlinear optical absorption coefficients and refractive index changes in double parabolic-square quantum well as dependent on intense laser field

In this study, for double parabolic-square quantum well (DPSQW) the linear and nonlinear intersubband optical absorption coefficients and the refractive index changes are calculated as dependent on the intense laser field (ILF). Our results show that the location and the size of all absorption coefficients and refractive index changes depend on ILF. Also, we show that ILF provides an important effect on the electronic and optical properties of DPSQW, and the changes of the energy levels and the dipole moment matrix elements are dependent on the shape of the confinement potential. Such effects can provide methods to drive tunable semiconductor lasers, which may be tailored by quantum potential well parameters and by ILF values.

Nonlinear intersubband absorption and refractive index change in n-type δ-doped GaAs for different donor distributions

In this study, both the linear and nonlinear intersubband optical absorption coefficients and the refractive index changes are calculated for the uniform, triangular and Gaussian-like donor distribution. The Gaussian-like distribution differs from the Gaussian distribution other authors use. The electronic structure of n-type Si δ-doped GaAs has been theoretically calculated by solving the Schrodinger and Poisson equations self-consistently. Our results show that the location and the size of the linear and total absorption coefficients and refractive index changes depend on the donor distribution type. The shape of δ-effective potential profile and the subband properties are changed as dependent on the donor distribution model. Therefore, the variation of the absorption coefficients and refraction index changes, which can be appropriate for various optical modulators and infrared optical device applications can be smooth obtained by the alteration donor distribution model.

Simultaneous effects of the intense laser field and the electric field on the nonlinear optical properties in GaAs/GaAlAs quantum well

In this study, both the linear and nonlinear intersubband optical absorption coefficients and the refractive index changes are calculated as dependent on the applied electric field (F) and the laser field intensity parameter (α0). Our results show that the location and the size of the linear and total absorption coefficients and refractive index changes depend on the applied external field effects. The shape of confined potential profile, the energy levels and the squared dipole moment matrix elements are changed as dependent on the F and α0. We have found that the intense laser field and the applied electric field can be used as a way to control the linear, nonlinear and total optical properties of the quantum well structures. While for F=0 the intersubband absorption spectrum shows blue-shift up to the critical laser field value ( for about α0<L/3), this spectrum shows red-shift for laser field values greater than this certain value. In the presence F, we obtain two critical laser field values (for about α0<L/3 and α0>2L/3). The absorption spectra display blue-shift up to the first critical laser field values, these spectra indicate red-shift up to the second critical values and show again blue-shift for the laser field values greater than these second certain values. Therefore, the variation of the absorption coefficients and refraction index changes which can be appropriate for various optical modulators and infrared optical device applications can be smooth obtained by the alteration of electric field and intense laser field.

Polaron effects on the linear and nonlinear intersubband optical absorption coefficients in quantum wells with asymmetrical semi-exponential potential

Linear and nonlinear intersubband optical absorption coefficients in quantum wells with asymmetrical semi-exponential potential are studied theoretically. We obtain unperturbed eigenfunctions and the energy eigenvalues by means of solving Schrödinger equation within the framework of effective mass approximation. The wave functions and energies with consideration of polaron are acquired through perturbation method. Besides, the analytic expressions of optical absorption coefficients are obtained using compact-density-matrix approach and iterative method. The results of calculation show that optical absorption is enhanced when effects of polaron are considered. Additionally, the parameters of confinement potential have great influences on optical absorption.

Effect of intense high-frequency laser field on the linear and nonlinear intersubband optical absorption coefficients and refractive index changes in a parabolic quantum well under the applied electric field

The effects of the intense high-frequency laser field on the optical absorption coefficients and the refractive index changes in a GaAs/GaAlAs parabolic quantum well under the applied electric field have been investigated theoretically. The electron energy levels and the envelope wave functions of the parabolic quantum well are calculated within the effective mass approximation. Analytical expressions for optical properties are obtained using the compact density-matrix approach. The numerical results show that the intense high-frequency laser field has a large effect on the optical characteristics of these structures. Also we can observe that the refractive index and absorption coefficient changes are very sensitive to the electric field in large dimension wells. Thus, this result gives a new degree of freedom in the optoelectronic device applications.

Polaron effect on linear and nonlinear intersubband optical absorption of a wurtzite GaN-based nanowire

Based on the density matrix approach and the perturbation treatment, the polaronic effect on the linear and nonlinear intersubband optical absorption coefficients in quasi-one-dimensional wurtzite nanowires (NWs) is investigated. The simple analytical formulas for polaronic states and the linear and nonlinear optical absorption coefficients in the NW systems are also deduced. Numerical calculation on a freestanding wurtzite GaN NW is performed. The polaronic effect and quantum size effect as well as the influence of incident optical intensity on the optical absorption properties are analyzed and discussed. The results show that, the polaronic effect results in significant increase of the absorption coefficients, and obvious decrease of saturation absorption intensity. In order to observe strong optical absorption, a nitride NW with relative small radius should be chosen. Moreover, a comparison with the situation of GaN-based quantum well systems is also done, and the profound physics is analyzed reasonably. • Polaronic states including the IO and QC phonon modes in wurtzite nitride NWs are obtained. • Polaronic effect results in significant increase of the linear and nonlinear absorption coefficients. • Taking the polaronic effect into account, saturation absorption intensity decreases obviously. • GaN-based NWs with smaller radius should be chosen for observing stronger optical absorption.

Linear and nonlinear intersubband optical absorption coefficient and refractive index change in n-type δ-doped GaAs structure

In the effective mass approximation, we have theoretically investigated the subband structure of single Si δ-doped GaAs by solving the Schrödinger and Poisson equations self-consistently. Both the linear and nonlinear intersubband optical absorption coefficients and the refractive index changes are calculated as dependent on the doping concentration and thickness. Our results show that the position and the magnitude of the linear and total absorption coefficients and refractive index changes depend on the doping concentration and thickness. The shape of potential profile and the subband energy differences are changed as dependent on the donor concentration and thickness. By considering the variation of the energy difference we can obtain a blue shift or a red shift in the intersubband optical transitions. The resonant peak of total absorption coefficient can be bleached at sufficiently high incident optical intensities. Such a dependence of the exciting optical intensity on the doping concentration and thickness can be very useful for several potential device applications.

Nonlinear Optical Spectra of Intersubband Transitions in a CdSe/ZnS/CdSe/SiO2 Spherical Quantum Dot

In this paper the electronic spectra and optical properties of one-electron spherical quantum dot (QD) are presented. QD is composed of CdSe core surrounded by ZnS shell (barrier) CdSe shell and finally by medium of very high potential barrier (SiO2) compared to CdSe. The energy eigenvalues of s, p and d states and corresponding wave functions were calculated using effective mass approximation. We have calculated oscillator strengths and the linear and third-order nonlinear intersubband optical absorption coefficients as function of the QD dimension, incident photon energy and incident optical intensity for the 1s-1p, 1p-1d and 1p-2s transitions.

Linear and nonlinear intersubband optical absorption coefficients and refractive index changes with the ring-shaped non-spherical oscillator potential

Linear and nonlinear intersubband optical absorption coefficients and refractive index changes with the ring-shaped non-spherical oscillator potential (RNOP) are theoretically investigated within the framework of the compact-density-matrix approach and iterative method. The energy levels and the wave functions of an electron in the RNOP are obtained by using the effective mass approximation. It is found that the optical absorption coefficients and refractive index changes are strongly affected not only by the dimensionless parameters γ and β, but also by the confinement frequency ω0.

Influence of the internal heterostructure on nonlinear absorption spectra for intersubband transitions in spherical quantum dot–quantum well nanoparticles

In this paper, we present the results of our investigation of the electronic spectra and optical properties of one-electron spherical quantum dot–quantum well (QDQW) structure. The investigated QDQW system consists of a CdSe core surrounded by a ZnS shell and a CdSe shell and capped by material of a very high electron potential barrier compared to CdSe, i.e. CdSe/ZnS/CdSe structure. Eigenenergies and corresponding wave functions were calculated by the effective mass approximation. We focused on the one-electron ground state (1s) and the first three excited states. For the allowed transitions, we have calculated the linear and third-order nonlinear intersubband optical absorption coefficients for various structures, i.e. different CdSe core radii, ZnS shell (barrier) widths and CdSe shell widths. A change in the core and shells dimensions induces a change in the electron wave function, followed by a significant change in the energy of state. As a result, the optical properties of this system are strongly dependent on the QDQW structure.

Linear and nonlinear intersubband optical absorption coefficients and refractive index changes in symmetric double semi-V-shaped quantum wells

In this study, the changes in the refractive index and intersubband optical absorption coefficients in symmetric double semi-V-shaped quantum wells are investigated theoretically. The energy levels and the envelope wave functions of an electron confined in finite potential double semi-V-shaped quantum wells are calculated within the effective-mass approximation framework. The analytical expressions of the refractive index and intersubband optical absorption coefficients are obtained using the compact density matrix approach. The effects of the incident optical intensity and structure parameters, such as the barrier width, confinement potential and the well width, on the optical properties of the double semi-V-shaped quantum wells are investigated. The numerical results show that both the incident optical intensity and structure paremeters have a great effect on the optical characteristics of these structures.