Intersubband Optical Absorption Coefficients Research Articles

Optical properties of a single quantum well with Pöschl–Teller confinement potential

In this work, using the compact density matrix approach and iterative procedure, the effects of the two asymmetry parameters of the Pöschl-Teller quantum well (QW) on the nonlinear optical rectification (NOR), second harmonic generation (SHG), third harmonic generation (THG), inter-subband optical absorption coefficient (IOAC), and refractive index change (RIC) are studied. Numerical results reveal that the two asymmetry parameters ν and μ of the Pöschl-Teller QW have a great influence on the NOR, SHG, THG, IOACs, and RICs. The maximum asymmetry of the Pöschl-Teller confinement potential can be gotten by an optimized set of two ν and μ asymmetry parameters. If it is desired to obtain the NOR, SHG, THG, and total RIC (IOAC) with larger values, then a relatively small (large) value of μ / ν should be employed. Significant high-order nonlinear can be obtained via a correct choice of the set of the two asymmetry parameters. The results of our study show that the Pöschl-Teller QW is a promising candidate for optoelectronic device applications. • The asymmetry parameters ( ν and μ ) of the Pöschl-Teller QW have great influences on the NOR, SHG, THG, ACs, and RICs. • The maximum asymmetry of the Pöschl-Teller confinement potential can be gotten by an optimized set of ν and μ . • If it is desired to obtain the NOR, SHG, THG, and total RIC (IOAC) with larger values, then a relatively small (large) value of ν and μ should be employed. • Significant high-order nonlinear can be obtained via a correct choice of the set of ν and μ . • The results of our study show that the Pöschl-Teller QW is a promising candidate for optoelectronic device applications.

Linear and nonlinear optical properties in wurtzite MgZnO/ZnO double quantum wells: Roles of external electric and magnetic fields

In this work, the modulation effects of external magnetic and electric fields on the inter-subband optical absorption coefficients and refractive index changes in asymmetric wurtzite MgZnO/ZnO double quantum wells are investigated considerably. The linear and nonlinear characteristics among the three lowest confined states are calculated here. The obtained results show that the optical properties of the structure are very sensitive to the external field. The optical characteristics related to higher energy levels which have been ignored in past works are as important as the transition related to the ground state. The transition from the ground state to the second excited state is the most sensitive to the external fields. The optical parameters can be risen by two orders of magnitude through the manipulation of the applied electric and magnetic fields.

Nonlinear optical absorption and refractive index change in realistic [formula omitted] V-groove quantum wires

The intersubband optical absorption coefficient and refractive index change of a realistic single-electron GaAs/Ga1−xAlx V-groove quantum wire are calculated. Finite confinement potentials and analytic models capable of adapting to many V-groove quantum wire shapes reported in the literature are used in the calculations. This scheme allows analyzing the effect of the inter-sidewall angle and crescent thickness on the optical response. Additionally, the effects of external fields such as hydrostatic pressure and temperature are taken into account. The results show that the geometrical parameters have a principal role compared to the temperature and hydrostatic pressure. In addition, optical activity within the Terahertz band using the parameter values that fit the typically V-groove quantum wires reported in the literature was found.

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.

Impurity photoionization cross-section and intersubband optical absorption coefficient in multilayer spherical quantum dots

Energy spectrum, wave functions and binding energies of the electron to the donor impurity ion located in the center of a multilayer spherical quantum dot (MSQD) consisting of a core and two spherical shells were studied within the effective mass approximation. Based on the exact wave functions of the electron expressed in terms of Coulomb functions of the first and second kind, the spectral dependences of the photoionization cross section of the impurity (PCS) and the intersubband optical absorption coefficient (OAC) for various geometric dimensions of the nanostructure were calculated. It is shown that the decrease in the width of the external potential well changes the localization of the electron in the nanosystem which significantly affects the binding energy of the electron with the impurity, photoionization cross section and interband absorption coefficient. The position of the PCS peak associated with the quantum transition of an electron from the ground state to the 1p0 state shifts to the region of higher energies, and its height decreases. At the same time, the height of PCS peaks associated with quantum transitions to higher excited states (2p0, 3p0) increases.The presence of impurities and changes in the MSQD size significantly affect the intersubband absorption coefficient. Decrease of the external potential well width in the absence of impurities leads to a monotonous increase in OAC through the first excited state, and in the presence of a central impurity, absorption through states with higher energy increases.

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.

Tunneling influence on the intersubband optical absorption coefficient and refraction index in biased GaAs/AlGaAs quantum well wires

We investigate the tunnel effect influence on the intersubband optical absorption and refraction in a gallium arsenide quantum well wire in transverse electric field. The quasi-stationary energy levels and escape times are obtained using the complex eigenvalue study in a two-dimensional finite element method. The linear absorption coefficient and the relative change of the refractive index are calculated according to the Fermi's golden rule and by involving the intersubband relaxation time. Our work shows that the electronic linewidth broadening related to the carrier tunneling has a major effect on the optical absorption lines, especially for intense electric fields. Absorption peaks are blue-shifted by the increasing electric field and, at the same time, they are enlarged and decreased in amplitude. A field-invariable relaxation rate, as is assumed by many previous theoretical studies, could not be justified, even for moderate electric fields.

Bound states and optical properties for Derjaguin-Landau-Verweij-Overbook potential

In the present work, bound states of the Schrodinger equation (SE) and the corresponding optical properties for Derjaguin-Landau-Verweij-Overbook (DLVO) potential are studied. For this goal, we first solved the SE using DLVO potential and obtained eigenfunctions and bound state energy eigenvalues for an arbitrary system. We used analytical expression for optical properties obtained by the compact-density matrix formalism. Here, we have investigated the intersubband optical absorption coefficients and refractive index changes.

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.

Terahertz intersubband transitions in GaAsBi/AlGaAs single quantum well heterostructure

Abstract GaAsBi/AlGaAs single quantum well conduction band structure, energy levels, and their corresponding wavefunctions have been calculated by solving the Schrodinger equation. The influences of the heterostructure parameters on the intersubband transition (ISBT) frequency within the terahertz (THz) domain have been investigated. The results show that the quantum well width has a great impact on the THz ISBT frequency. In particular, an ISBT with a frequency of 2.611 THz (10.80 meV) has been obtained for specifically optimized parameters. The study of the intersubband optical absorption coefficient (OAC) was centered in the frequency band of 2–14 THz (~8–58 meV), therefore the corresponding results are useful for the optimization of THz detectors. Correspondingly, by changing the thickness of the active layer the number of the OAC peaks has been tuned. The dipole matrix element and the Fermi occupation function have been also studied in detail. Furthermore, the influences coming from the incidence angle on the OAC intensity were numerically investigated. The obtained results could be beneficial for the design and the optimization of devices operating in the THz frequency band.

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.

The Combined Influence of Hydrostatic Pressure and Temperature on Nonlinear Optical Properties of GaAs/Ga0.7Al0.3As Morse Quantum Well in the Presence of an Applied Magnetic Field.

Studies aimed at understanding the nonlinear optical (NLO) properties of GaAs/Ga0.7Al0.3As morse quantum well (QW) have focused on the intersubband optical absorption coefficients (OACs) and refractive index changes (RICs). These studies have taken two complimentary approaches: (1) The compact-density-matrix approach and iterative method have been used to obtain the expressions of OACs and RICs in morse QW. (2) Finite difference techniques have been used to obtain energy eigenvalues and their corresponding eigenfunctions of GaAs/Ga0.7Al0.3As morse QW under an applied magnetic field, hydrostatic pressure, and temperature. Our results show that the hydrostatic pressure and magnetic field have a significant influence on the position and the magnitude of the resonant peaks of the nonlinear OACs and RICs. Simultaneously, a saturation case is observed on the total absorption spectrum, which is modulated by the hydrostatic pressure and magnetic field. Physical reasons have been analyzed in depth.

Intersubband optical absorption of electrons in double parabolic quantum wells of AlxGa1−xAs/AlyGa1−yAs**Project supported by the National Natural Science Foundation of China (Grant No. 61274098).

Some realizable structures of double parabolic quantum wells (DPQWs) consisting of AlxGa1−xAs/AlyGa1−yAs are constructed to discuss theoretically the optical absorption due to the intersubband transition of electrons for both symmetric and asymmetric cases with three energy levels of conduction bands. The electronic states in these structures are obtained using a finite element difference method. Based on a compact density matrix approach, the optical absorption induced by intersubband transition of electrons at room temperature is discussed. The results reveal that the peak positions and heights of intersubband optical absorption coefficients (IOACs) of DPQWs are sensitive to the barrier thickness, depending on Al component. Furthermore, external electric fields result in the decrease of peak, and play an important role in the blue shifts of absorption spectra due to electrons excited from ground state to the first and second excited states. It is found that the peaks of IOACs are smaller in asymmetric DPQWs than in symmetric ones. The results also indicate that the adjustable extent of incident photon energy for DPQW is larger than for a square one of a similar size. Our results are helpful in experiments and device fabrication.

Linear intersubband optical absorption in the semiparabolic quantum wells based on AlN/AlGaN/AlN under a uniform electric field

The linear intersubband optical absorption in the polarization semiparabolic quantum wells (SPQWs) are investigated for typical AlN/AlxGa 1−x N/AlN. First, the one-dimensional Poisson and Schrödinger equations have been solved by the variational method within a finite potential barrier model and a bent band figured by all confinement sources (realistic model). Then, the intersubband optical absorption between the lowest two subbands has been theoretically studied under an uniform external electric field. Computed results including the effective confining potential profile, the wave function and the distribution of electron gas in quantum wells, intersubband optical absorption coefficient have been discussed. Our calculation shows that the positive interface polarization charges affect on the distribution of the two-dimensional electron gas (2DEG) in SPQWs so it has great influences on the total optical absorption coefficients significantly.

Study of nonlinear optical absorption in GaN/AlGaN core–shell nanowire

The effect of aluminum mole fraction and incident light intensity on linear, nonlinear, and total optical absorption coefficients in GaN / Al x Ga 1 − x N core-defected shell nanowire is theoretically investigated. The presented nanostructure is a cylindrical quantum wire including a defected shell around the cylinder core. Based on the density matrix approach and the effective mass approximation, the intersubband optical absorption coefficients are numerically calculated. The results show that the magnitude and peaks positions of optical absorption coefficients can be adjustable by varying aluminum mole fraction. The resonance peak positions of optical absorption coefficients are blueshifted by increasing of the shell region potential due to increasing of the energy difference between two energy levels.

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.