Spin Polaron in a Diluted Parabolic Magnetic Quantum Well

在在做超点阵系统 Cd1 xin Mn1 xout Te/Cd1 xout Mnxout Te 的旋转好的量的旋转极化子的理论调查在这份报纸被介绍。在有效集体近似以内的一个变化过程被采用面对磁性坚持计算施主电离精力。旋转 polaronic 移动用一个吝啬的保持的理论被估计。施主绑定精力(i) 在井尺寸(ii ) 与减小增加的结果表演减少与磁性成立被增加因为给定的井宽度(iii ) 在 90 点增加到最大的价值吗？然后超过 90 作为井增加的尺寸减少？并且(iv ) 旋转 polaronic 转移减少到施主绑定精力在不仅一磁性成立而且与井宽度。结果与存在相比是可得到的文学。

The nonlinear optical properties of a magneto-exciton in a strained Ga_(0.2)In_(0.8)As/GaAs quantum dot

The magnetic field-dependent heavy hole excitonic states in a strained Gao.2Ino.sAs/GaAs quantum dot are investi- gated by taking into account the anisotropy, non-parabolicity of the conduction band, and the geometrical confinement. The strained quantum dot is considered as a parabolic dot of InAs embedded in a GaAs barrier material. The dependence of the effective excitonic g-factor as a function of dot radius and the magnetic field strength is numerically measured. The interband optical transition energy as a function of geometrical confinement is computed in the presence of a mag- netic field. The magnetic field-dependent oscillator strength of interband transition under the geometrical confinement is studied. The exchange enhancements as a function of dot radius are observed for various magnetic field strengths in a strained Gao.2Ino.sAs/GaAs quantum dot. Heavy hole excitonic absorption spectra, the changes in refractive index, and the third-order susceptibility of third-order harmonic generation are investigated in the Gao.2Ino.8As/GaAs quantum dot. The result shows that the effect of magnetic field strength is more strongly dependent on the nonlinear optical property in a low-dimensional semiconductor system.

Radiative life time of an exciton confined in a strained GaN/Ga_(1-x)Al_xN cylindrical dot:built-in electric field effects

The binding energy of an exciton in a wurtzite GaN/GaAlN strained cylindrical quantum dot is investigated theoretically. The strong built-in electric field due to the spontaneous and piezoelectric polarizations of a GaN/GaAlN quantum dot is included. Numerical calculations are performed using a variational procedure within the single band effective mass approximation. Valence-band anisotropy is included in our theoretical model by using different hole masses in different spatial directions. The exciton oscillator strength and the exciton lifetime for radiative recombination each as a function of dot radius have been computed. The result elucidates that the strong built-in electric field influences the oscillator strength and the recombination life time of the exciton. It is observed that the ground state exciton binding energy and the interband emission energy increase when the cylindrical quantum dot height or radius is decreased, and that the exciton binding energy, the oscillator strength and the radiative lifetime each as a function of structural parameters （height and radius） sensitively depend on the strong built-in electric field. The obtained results are useful for the design of some opto-photoelectronic devices.

Nonlinear Optical Properties in a Quantum Dot of Some Polar Semiconductors

Exciton binding energy,interband emission energy,oscillator strength,and some nonlinear optical properties in quantum dots made up of polar semiconductors are computed with the geometrical confinement.The effects of the interaction of charge carriers with the longitudinal optical phonons on the exciton binding energy are included.The anisotropy of the effective masses of holes is incorporated throughout the calculations.Nonlinear optical exciton absorption of Ⅱ–Ⅵ systems based on some polar semiconductors in the presence of LO phonons is discussed.The optical rectification coefficient associated with the intersubband transitions in a quantum dot of polar semiconductors is investigated.Changes of refractive index with the photon energy in a polar quantum dot are found.Our results show that the polar bound excitons in Ⅱ–Ⅵ based polar semiconductors depend on the geometrical confinement,and the nonlinear optical properties strongly depend on the polar materials.

Photo-Induced Electron Spin Polarization in a Narrow Band Gap Semiconductor Nanostructure

Photo-induced spin dependent electron transmission through a narrow gap InSb/InGa_(x)Sb_(1-x) semiconductor symmetric well is theoretically studied using transfer matrix formulism.The transparency of electron transmission is calculated as a function of electron energy for different concentrations of gallium.Enhanced spin-polarized photon assisted resonant tunnelling in the heterostructure due to Dresselhaus and Rashba spin-orbit coupling induced splitting of the resonant level and compressed spin-polarization are observed.Our results show that Dresselhaus spin-orbit coupling is dominant for the photon effect and the computed polarization efficiency increases with the photon effect and the gallium concentration.

Energy Gap Dependence on Mn Content in a Diluted Magnetic Quantum Dot

Positively charged donor exciton binding energy is computed as a function of quantum-dot size within the single band effective mass approximation for different Mn contents in Cd_(1)−x_(𝑥in)Mn_(x𝑥in)Te/Cd_(1−xout)𝑥outMn_(xout)𝑥outTe.The exciton bound polaron is computed for 0≤x𝑥≤0.08,on the Mn mole fraction.We determine the energy gap using the mean field approximation and incorporate the exchange interaction between the carrier and the magnetic impurity.The interband emission energy is studied with the height and radius of the cylindrical quantum dot.Valence-band anisotropy is included in our theoretical model using different hole masses in different spatial directions.Spin polaronic shifts as functions of quantum-dot radius and Mn concentration are estimated using the mean field theory.It is found that(i)the energy gap depends on the Mn mole fraction,(ii)it increases linearly with an increase in Mn content,and(iii)the effect is more pronounced for a narrow dot,showing the quantum size effects.Our results are in good agreement with other recently published reports.

Electronic and optical properties of CdS/CdZnS nanocrystals

Cd1-xZnxS nanocrystals are prepared by a co-precipitation method with different atomic fractions of Zn. The texture, structural transformation and optical properties with increasing x value in Cd1-xZnxS are studied with scanning electron microscopy, electron diffraction patterning, and absorption spectra respectively. Quantum confinement in a strained CdS/Cd1-xZnxS related nanodot with various Zn content values is investigated theoretically. Binding energies on exciton bound CdS/CdxZn1-xS quantum dot are computed, with consideration of the internal electric field induced by the spontaneous and piezoelectric polarizations, and thereby the interband emission energy is calculated as a function of the dot radius. The optical band gap from the UV absorption spectrum is compared with the interband emission energy computed theoretically. Our results show that the average diameter of composite nanoparticles ranges from 3 nm to 6 nm. The X-ray diffraction pattern shows that all the peaks shift towards the higher diffracting angles with an increase in Zn content. The lattice constant gradually decreases as the Zn content increases. The strong absorption edge shifts towards the lower wavelength region and hence the band gap of the films increases as the Zn content increases. The values of the absorption edge are found to shift towards the shorter wave length region and hence the direct band gap energy varies from 2.5 eV for the CdS film and 3.5 eV for the ZnS film. Our numerical results are in good agreement with the experimental results.

Polaron Effect of a Two Electron Parabolic Quantum Dot

Polaron induced double electron in a quantum dot is investigated using the exact diagonalization techniques and the compact density-matrix approach. The dependence of nonlinear optical processes on the incident photon energies and the polaronic effect are brought out. The linear, third order non-linear optical absorption coefficients and the refractive index changes of singlet and triplet states as a function of photon energy are obtained with and without the inclusion of polaronic effect. It is found that the geometrical confinement and the effect of polaron have great influence on the optical properties of dots.

Differential optical gain in a GaInN/AlGaN quantum dot

Electronic and optical properties are obtained with the increase in indium alloy content（x）in a Ga1-xInxN/Al0.2Ga0.8N quantum dot.The barrier height with the different In alloy contents is applied to acquire the confinement potentials.The results are obtained taking into consideration geometrical confinement effect.The optical absorption coefficient with the photon energy is observed in a Ga（1-x）InxN/Al0.2Ga0.8N quantum dot.The optical output with the injection current density and the threshold optical pump intensity for various In alloy contents are studied.The differential gain as functions of indium alloy content,charge density and the dot radii in the Ga1-xInxN/Al0.2Ga0.8N quantum dot are investigated.The exciton binding energy is calculated in order to obtain the exciton density,the optical gain and the threshold current density in the Ga1-xInxN/Al0.2Ga0.8N quantum dot.The results show that the red shift energy with an increase in In alloy content is found and the differential gain increases with the charge carrier density.

Magneto-polaron induced intersubband optical transition in a wide band gap Ⅱ–Ⅵ semiconductor quantum dot

Effects of LO-phonon contribution on the electronic and the optical properties are investigated in a Cdo.sZno.2 Se/ZnSe quantum dot in the presence of magnetic field strength. The magneto-polaron induced hydro- genic binding energy as a function of dot radius in the wide band gap quantum dot is calculated. The oscilla- tor strength and the spontaneous lifetime are studied taking into account the spatial confinement, magnetic field strength and the phonon contribution. Numerical calculations are carried out using variational formulism within the single band effective mass approximation. The optical properties are computed with the compact density matrix method. The magneto-polaron induced optical gain as a function of photon energy is observed. The results show that the optical telecommunication wavelength in the fiber optic communications can be achieved using CdSe/ZnSe semiconductors and it can be tuned with the proper applications of external perturbations.

Effect of p-d exchange with an itinerant carrier in a GaMnAs quantum dot

Hydrogenic acceptor binding energy as a function of dot radius in a GaMnAs/Ga_（0.6）Al_（0.4）As quantum dot is calculated including the exchange interaction of Mn alloy content with an itinerant carrier.Calculations are performed by varying its dot radius,for various Mn alloy contents in GaMnAs quantum dot within a single band effective mass approximation using variational method.The spin polaronic energy of the acceptor impurity for different Mn^（2＋） is evaluated for different dot radii using a mean field theory in the presence of magnetic field strength.The magnetization is computed in the influence of magnetic field and the Mn ions.The effective g-factor of the valence band electron with the inclusion of effects of Mn ion impurities is found in the influence of the magnetic field.The exchange coupling constant is calculated for various magnetic field strengths.The results show that the p-d exchange interaction in the GaMnAs/Ga_（0.6）Al_（0.4）As quantum dot has a strong dependence on spatial confinement,effect of magnetic field strength and the Mn alloy content.Our results are in good agreement with the other investigators.

Dielectric confinement on exciton binding energy and nonlinear optical properties in a strained Zn_(1-x_(in))Mg_(x(in))Se/Zn_(1-x(out))Mg_(x(out))Se quantum well

The band offsets for a Zn1-xin Mgxin Se/Zn1-xout Mgxout Se quantum well heterostructure are determined using the model solid theory. The heavy hole exciton binding energies are investigated with various Mg alloy contents. The effect of mismatch between the dielectric constants between the well and the barrier is taken into account. The dependence of the excitonic transition energies on the geometrical confinement and the Mg alloy is discussed. Non-linear optical properties are determined using the compact density matrix approach. The linear, third order non-linear optical absorption coefficient values and the refractive index changes of the exciton are calculated for different concentrations of magnesium. The results show that the occurred blue shifts of the resonant peak due to the Mg incorporation give the information about the variation of two energy levels in the quantum well width.