共查询到20条相似文献,搜索用时 15 毫秒
1.
Wenfang Xie 《Optics Communications》2009,282(13):2604-1133
A investigation of the linear and nonlinear optical properties of an exciton in a spherical parabolic quantum dot has been performed by using the matrix diagonalization method. The optical absorption coefficients between the ground state (L=0,π=+1) and the first excited state (L=1,π=-1) have been examined based on the computed energies and wave functions. The results are presented as a function of the incident photon energy for the different values of the incident optical intensity and the confinement strength. We found the optical absorption coefficient is strongly affected by the incident optical intensity and the confinement strength. 相似文献
2.
Bekir Çak?r Yusuf Yakar Ayhan Özmen M. Özgür Sezer Mehmet ?ahin 《Superlattices and Microstructures》2010
The binding energy and wavefunctions of the 1s, 1p, 1d and 1f energy states of a spherical quantum dot (QD) with parabolic potential were calculated by using a method which is a combination of the quantum genetic algorithm (QGA) and the Hartree–Fock–Roothaan (HFR) approach. In addition, the linear and the third-order nonlinear optical absorption coefficients based on optical transitions in QDs with and without impurity were calculated. The results show that the parabolic potential has a great effect not only on the binding energies and but also on the optical absorption coefficients. Moreover, the calculated results also reveal that the linear and nonlinear optical absorption coefficients are strongly affected by the existence of impurity and the incident optical intensity. 相似文献
3.
The effects of spatially dependent effective mass, non-parabolicity of the conduction band and dielectric screening function on exciton binding energy in a pyramid-shaped quantum dot of GaAs have been investigated by variational method as a function of base width of the pyramid. We have assumed that the pyramid has a square base with area \(a\times a\) and height of the pyramid \(H=a/2\). The trial wave function of the exciton has been chosen according to the even mirror boundary condition, i.e. the wave function of the exciton at the boundary could be non-zero. The results show that (i) the non-parabolicity of the conduction band affects the light hole (lh) and heavy hole (hh) excitons to be more bound than that with parabolicity of the conduction band, (ii) the dielectric screening function (DSF) affects the lh and hh excitons to be more bound than that without the DSF and (iii) the spatially dependent effective mass (SDEM) affects the lh and hh excitons to be less bound than that without the SDEM. The combined effects of DSF and SDEM on exciton binding energy have also been calculated. The results are compared with those available in the literature. 相似文献
4.
In the effective mass approximation, we calculated the binding energy and wave function for the 1s-, 1p-, 1d- and 1f-states of a spherical quantum dot (QD) with parabolic potential by using a combination of quantum genetic algorithm (QGA) and Hartree-Fock-Roothaan (HFR) method. In addition, we also investigated the linear and the third-order nonlinear optical absorption coefficients as a function of the incident photon energy for the 1s-1p, 1p-1d and 1d-1f transitions. Our results are shown that the existence of impurity has great influence on optical absorption coefficients. Moreover, the optical absorption coefficients are strongly affected by the incident optical intensity, relaxation time, parabolic potential and dot radius. 相似文献
5.
Wenfang Xie 《Optics Communications》2011,284(7):1872-42
The nonlinear optical properties of a D− system confined in a spherical quantum dot represented by a Gaussian confining potential are studied. The great advantage of our methodology is that the model potential possesses the finite height and range. Calculations are carried out by using the method of numerical diagonalization of Hamiltonian matrix within the effective-mass approximation. We calculate the linear, third-order nonlinear and total optical absorption coefficients under the density matrix formalism. Numerical results for GaAs − Ga1 − xAlxAs QDs are presented. Our results show that the optical absorption coefficients in a spherical QD are much larger than their values for GaAs quantum wells. It is found that optical absorptions are strongly affected not only the confinement barrier height, dot radius, the electron-impurity interaction but also the position of the impurity. 相似文献
6.
7.
Dipole-allowed optical absorption in a parabolic quantum dot with two electrons are studied by using the exact diagonalization techniques and the compact density-matrix approach. Numerical results are presented for typical GaAs parabolic quantum dots. The results show that the total optical absorption coefficient of two electrons in quantum dot is about five times smaller than that of one electron in quantum dot. 相似文献
8.
We present a variational calculation for the ground state of the double donor in a spherical GaAs–Ga1–x
Al
x
As quantum dot. The binding energies for the ionized and neutral centres are calculated for several barrier height values as a function of the radius of the dot. Compared with a square well structure, there is a stronger confinement and a larger binding energy for the double donors in a spherical quantum dot. 相似文献
9.
We analyze the exciton states in a quantum wire under intense laser radiation. Electrons and holes are confined by the parabolic potential of the quantum wire. An exactly solvable model is introduced for calculating the exciton binding energy, replacing the actual Coulomb interaction between the electron and the hole by a projective operator. 相似文献
10.
In this study, we have calculated the linear, nonlinear and total refractive index changes and absorption coefficients for the transitions 1s–1p, 1p–1d and 1d–1f in a spherical quantum dot with parabolic potential. Quantum Genetic Algorithm (QGA) and Hartree–Fock–Roothaan (HFR) method have been employed to calculate the wavefuctions and energy eigenvalues. The results show that impurity, dot radius, stoichiometric ratio, incident optical intensity and carrier density of the system have important effects on the optical refractive index changes and absorption coefficients. Also, we find that as the transitions between orbitals with big l value move to lower energy region in case with parabolic potential, in case without parabolic potential these transitions move to higher energy region. 相似文献
11.
A bound polaron in a spherical quantum dot 总被引:12,自引:0,他引:12
H.-J. Xie C.-Y. Chen 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,5(2):215-218
The binding energy of a bound polaron in a spherical quantum dot has been investigated by using the variational method. The
influence of LO and SO phonons have taken into consideration. Result shows that the phonon contribution to the binding energy
is dependent on the size of the quantum dot as well as the position of the impurity in the quantum dot. Numerical calculation
on the ZnSe quantum dot shows that such contribution is about 5% to 20% of the total binding energy.
Received: 13 October 1997 / Revised: 4 March 1998 / Accepted: 26 May 1998 相似文献
12.
K. Mathan Kumar A. John Peter C. W. Lee 《The European Physical Journal B - Condensed Matter and Complex Systems》2011,84(3):431-438
Electronic energies of an exciton confined in a strained
Zn1−x
Cd
x
Se/ZnSe quantum dot have
been computed as a function of dot radius with various Cd content. Calculations have been
performed using Bessel function as an orthonormal basis for different confinement
potentials of barrier height considering the internal electric field induced by the
spontaneous and piezoelectric polarizations. The optical absorption coefficients and the
refractive index changes between the ground state (L = 0) and the first
excited state (L = 1) are investigated. It is found that the optical
properties in the strained ZnCdSe/ZnSe quantum dot are strongly affected by the
confinement potentials and the dot radii. The intensity of the total absorption spectra
increases for the transition between higher levels. The obtained optical nonlinearity
brings out the fact that it should be considered in calculating the optical properties in
low dimensional semiconductors especially in quantum dots. 相似文献
13.
《Current Applied Physics》2008,8(2):153-158
Within the framework of effective-mass approximation, exciton states confined in zinc-blende(ZB) InGaN/GaN quantum dot(QD) are investigated by means of a variational approach, considering finite band offsets. The ground-state exciton binding energy and the interband emission energy are investigated as functions of QD structural parameters in detail. Numerical results show clearly that both the QD size and In content of InGaN have a significant influence on the exciton states and interband optical transitions in the ZB InGaN/GaN QD. 相似文献
14.
Within the framework of the effective-mass approximation, the exciton states and interband optical transitions in InxGa1−xN/GaN strained quantum dot (QD) nanowire heterostructures are investigated using a variational method, in which the important built-in electric field (BEF) effects, dielectric-constant mismatch and three-dimensional confinement of the electron and hole in InxGa1−xN QDs are considered. We find that the strong BEF gives rise to an obvious reduction of the effective band gap of QDs and leads to a remarkable electron-hole spatial separation. The BEF, QD height and radius, and dielectric mismatch effects have a significant influence on exciton binding energy, electron interband optical transitions, and the exciton oscillator strength. 相似文献
15.
A. Kh. Manaselyan A. V. Ghazaryan A. A. Kirakosyan 《Journal of Contemporary Physics (Armenian Academy of Sciences)》2008,43(5):211-217
We consider the electron and hole states in a semiconductor ZnSe spherical quantum dot, in the center of which a magnetic impurity atom of manganese is located. In calculations the quantum dot is approximated by a spherical rectangular well with a finite depth. Within the framework of perturbation theory, the effect of exchange spin interaction of an electron and a hole with a magnetic impurity on the band structure of the system is considered. The optical spectrum of the system for different polarizations of the incident light is studied also. 相似文献
16.
Spherical quantum dots containing several electrons are considered for different values of the total spin. Numerical calculations are carried out using the quantum path-integral Monte Carlo method. The dependence of the electron correlations on the dimensionless control quantum parameter q associated with the steepness of the confinement potential is studied. The quantum transition from a Wigner crystal-like state (i.e., from the regime of strongly correlated electrons) to a Fermi-liquid state (“cold” melting) driven by the parameter q is studied in detail. The behavior of the radial and pair correlation functions, which characterize quantum delocalization of the electrons, is considered. 相似文献
17.
This paper calculates the lifetime of resonant state and
transmission probability of a single electron tunnelling in a
spherical quantum dot (SQD) structure by using the transfer matrix
technique. In the SQD, the electron is confined both transversally
and longitudinally, the motion in the transverse and longitudinal
directions is separated by using the adiabatic approximation theory.
Meanwhile, the energy levels of the former are
considered as the
effective confining potential. The numerical calculations are carried out
for the SQD consisting of GaAs/InAs material. The obtained results show that the
bigger radius of the quantum dot not only leads significantly to the shifts
of resonant peaks toward the low-energy region, but also causes the
lengthening of the lifetime of resonant state. The lifetime of resonant
state can be calculated from the uncertainty principle between the energy
half width and lifetime. 相似文献
18.
《Superlattices and Microstructures》1993,13(3):315
The absorption coefficient spectrum of undoped, disordered InGaAs/GaAs single quantum wells is calculated within the parabolic band approximation in this compressively strained structure. Results are presented for light propagating normal to and along the plane of the quantum well, taking into consideration the 1S-like exciton and all bound states, including the 2D enhancement Sommerfeld factor. The results presented here show that the exciton peaks in TE polarization remain constant with disordering and exhibit a larger wavelength shift than in TM polarization. The absorption edge in disordered InGaAs/GaAs, which is a function of the strain and interdiffusion, can be tailored to the desired wavelength around 1.0 μm. These results can be of interest in the design of photonic devices on a single substrate. 相似文献
19.
Karen G. Dvoyan 《Physica B: Condensed Matter》2012,407(1):131-135
Confined states of a positronium (Ps) in the spherical quantum dot (QD) are theoretically investigated in three size-quantization (SQ) regimes: strong, weak and intermediate. In the strong SQ regime, analytical expressions for the wave functions (WFs) and energy of the electron-positron pair are obtained. In the weak SQ regime, the Ps energy and binding energy are analytically calculated. To calculate the Ps energy in the intermediate SQ regime, variational and numerical methods are used. It is shown that, in the corresponding limits, the results obtained by variational method agree with those obtained in the strong and weak SQ regimes. 相似文献
20.
M.R.K. Vahdani 《Physics letters. A》2010,374(4):637-4599
Optical absorption coefficients and refractive index changes associated with intersubband transition in a parabolic cylinder quantum dot are theoretically investigated. In this regard, the electronic structure of the dot is studied using the one band effective mass theory, and by means of the compact-density matrix approach the linear and nonlinear optical absorption coefficients and refractive index changes are calculated. The effects of the size of the dot, optical intensity and electromagnetic field polarization on the optical absorption coefficient and refractive index changes are investigated. It is found that absorption and refractive index changes are strongly affected not only by the size of the dot but also by optical intensity and the electromagnetic field polarization. 相似文献