Effect of impurity on the absorption of a parabolic quantum dot with including Rashba spin–orbit interaction (original) (raw)
Related papers
Semiconductor quantum dots: Theory and phenomenology
Bulletin of Materials Science, 1999
Research in semiconductor quantum dots (q-dots) has burgeoned in the past decade. The size (R) of these q-dots ranges from 1 to 100 nm. Based on the theoretical calculations, we propose energy and length scales which help in clarifying the physics of this mcsoscopic system. Some of these length scales are: the Bohr exciton radius (a*), the carrier de Broglie and diffusion length (~'D and ID) , the polaron radius (ap), and the reduction factor modulating the optical matrix element (M). R <a a is an individual particle confinement regime, whereas the larger ones are exciton confinement regime wherein Coulomb interaction play an important role. Similarly a size-dependent dielectric constant ~(R) should be used for R <ap <a n. An examination of M reveals that an indirect gap material q-dot behaves as a direct gap material in the limit of very small dot size. We have carried out effective mass theory (EMT) calculations to estimate the charge density on the surface of the quantum dot. We present tight binding (TB) calculation to show that the energy upshift scales as 1/R x, where x is less than 2 and the exponent depends on the orientation of the crystallite.
Impurity Modulated Static Linear and First Nonlinear Polarizabilities of Doped Quantum Dots
ISRN Optics, 2012
We explore the pattern of linear and first nonlinear optical (NLO) response of repulsive impurity doped quantum dots harmonically confined in two dimensions. The dopant impurity potential chosen assumes Gaussian form. The quantum dot is subject to a static electric field. For some fixed values of transverse magnetic field strength (ωc), and harmonic confinement potential (ω0), the influence of impurity strength (V0), impurity stretch (ξ), and impurity location (r0) on the diagonal components of static linear (αxx and αyy), and the first NLO (βxxx and βyyy) responses of the dot are computed through linear variational route. The investigation reveals the crucial roles played by the various impurity parameters in modulating these optical responses. Interestingly, maximization in the first NLO responses has been observed for some particular dopant location and at some particular value of spatial stretch of the dopant.
Electro-Optical Properties of Quantum Dots with an Asymmetric Confinement
We show how to compute the optical response of a Quantum Dot with asymmetric parabolic confinement exposed to a constant electric field applied in the growth direction. The method uses the microscopic calculation of QD eigenfunctions and the macroscopic real density matrix approach to compute the electroabsorption. Results are computed for In 0.64 Al 0.36 As/Al 0.3 Ga 0.7 As Quantum Dots. We obtain asymmetrical Stark shift of the electroabsorption maximum and the dependence on QDs dimensions is also displayed. New effects in absorption line shapes are observed. Fair agreement with experiments is obtained.
Frontiers in Physics, 2022
Rashba effect may play an important role in the nonlinear optical properties of heterojunction quantum dots. In this work, we have theoretically examined the effects of Rashba spin-orbit interaction on an electron in a cylindrical core/shell quantum dot (CCSQD). The modifications of various properties of cylindrical core/shell quantum dot such as transition energies, dipole transition matrix elements and linear and nonlinear optical properties due to change in Rashba coupling parameter, magnetic field and effective Rydberg energy were studied. We solved the Schrödinger equation using numerical methods and obtained energy eigenvalues as functions of the aforementioned parameters. It was observed that, the magnetic field has a considerable effect on absorption coefficients and refractive index. It was also observed that increasing the magnetic field shifts the resonances towards higher energies. Additionally, increasing in the Rashba coupling coefficient (α R) was found out to result an increase in absorption coefficients and refractive index. Our results demonstrated that, we can manipulate optical properties of cylindrical core/ shell quantum dot using an external magnetic field.
Physica B: Condensed Matter, 2011
The theoretical investigation of linear and third-order nonlinear absorption coefficients and refractive index changes in the cylindrical quantum dot with two models of confinement potentials in axial direction, namely, modified Pöschl-Teller and Morse potentials, and parabolic potential in radial direction, have been considered in the presence of external electric and magnetic fields. The selection rules for intraband transitions have been obtained for both potentials in the presence and absence of external fields. The behavior of linear, nonlinear and total absorption spectra have been observed for different values of temperatures for both potentials taking into account electron population on energy levels. The effect of change in the direction of electric field on the absorption spectra have been investigated, and the asymmetric and symmetric characters of these potentials manifest themselves differently: the peak positions of absorption lines for Morse potential undergo blue and red shifts compared to the case when the external electric field is absent, while for the case of modified Pöschl-Teller potential the absorption lines have only red shift. The same dependencies have been obtained for refractive index changes for both potentials. The second and third harmonic generation coefficients as a function of the photon energy have been plotted both in the absence and presence of external fields.
Electron-related optical responses in triangular quantum dots
Physica E: Low-dimensional Systems and Nanostructures, 2014
Optical absorption and changes in refractive index in triangular quantum dots. The effective mass and parabolic band approximations have been used. The increase in the size of the dot leads to a red shift of optical properties. Also, an increment in the values of the off-diagonal electric dipole moment matrix. The increase of the amplitude of the optical absorption is observed.
Electronic states and light absorption in quantum dot molecule
2011
The electronic states and direct interband absorption of light in quantum dot molecule ͑QDM͒ consisting 4 or 5 QDs are investigated. The electron energy levels and wave functions are calculated. It is shown that the energy levels are split in azimuth direction. In the case of the presence of the central QD in QDM an additional splitting in the radial direction is revealed. The suggested method can be used to calculate the electronic states and light absorption of arbitrary number QDM. The results are useful for the application of the QDM to photoelectric devices.
Optical Absorption Coefficients in a Polar Quantum Dot Nanostructure
Journal of Computational and Theoretical Nanoscience, 2012
The ground state and low lying-excited state energies of a hydrogenic impurity located at the centre of a strained Zn 1−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. Photoionization cross section of hydrogenic impurity in a quantum dot is investigated. We study the oscillator strengths, the linear and third-order nonlinear optical absorption coefficients as a function of incident photon energy for 1s-1p and 1p-1d transitions. It is found that the optical properties in the strained ZnCdSe/ZnSe quantum dot are strongly affected by the incident photon energy, the confinement potentials and the dot radii and the optical transition energy which depends on the dot radii and the barrier height and tunes the resonant frequency.
Electronic transient processes and optical spectra in quantum dots for quantum computing
IEEE Transactions on Nanotechnology, 2004
Quantum dot systems are studied theoretically from the point of view of realization of quantum bit using the orbital state of electronic motion in a quantum dot. Attention is paid to several effects which can influence significantly the application of quantum dot electronic orbital states in quantum computing, for example, the effect of upconversion of the population and the incomplete depopulation of electronic orbital states, the effect of optical line broadening and presence of continuous background in optical spectra. Attention is also paid to the effect of upconversion of electronic population to the wetting-layer or above-barrier electronic states in quantum dot samples. Interaction of electrons with the longitudinal optical phonons is shown to play a significant role in these effects. Possible impact of these phenomena on the realization of quantum bit based on electronic orbital states in quantum dots is discussed.