A. John Peter

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.

Radiative life time of an exciton confined in a strained GaN/Ga1-xAlxN 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.

Spin Polarization Efficiency in a Diluted Magnetic Nano-Semiconductor Quantum Well System

Article history: Received 21 March 2018 Accepted 29 March 2018 Available online 06 April 2018 Diluted magnetic semiconductors (DMS) in which a fraction of non-magnetic cation is replaced by any transition metal ions. They are considered to have wide potential applications for magneto-optic devices. In the present work, the magnetic field is applied externally in a diluted magnetic semiconductor quantum well to investigate spin transmission properties. The material taken for the study is ZnMnSe/ZnSe quantum well. Rashba spin orbit interaction on the resonant spin polarized transport in this heterostructure quantum well is studied. The plane wave function of the electron is applied to obtain the energy eigen values. The mean field approximation is employed to investigate the interaction of the host electron and the localized magnetic impurities. The large polarization occurs in DMS due to the exchange interaction between the local magnetic impurity and the electrons and this effect lifts the degeneracy of spin-up and spin down electron states. The obtained results, on spin dependent tunneling, may be used in the spin based devices especially in the spin field effect transistors.

Investigations on Landé factor in a strained GaxIn1−xAs/GaAs quantum dot

The effective excitonic g-factor as functions of dot radius and the Ga alloy content, in a strained GaxIn1−xAs/GaAs quantum dot, is numerically measured. The heavy hole excitonic states are studied for various Ga alloy content taking into account the anisotropy, non-parabolicity of the conduction band and the geometrical confinement effects. The quantum dot is considered as spherical dot of InAs surrounded by a GaAs barrier material.

The nonlinear optical properties of a magneto-exciton in a strained Ga0.2In0.8As/GaAs quantum dot

The magnetic field-dependent heavy hole excitonic states in a strained Ga0.2In0.8As/GaAs quantum dot are investigated 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 magnetic 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 Ga0.2In0.8As/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 Ga0.2In0.8As/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.

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 Cd1−xinMnxin Te/Cd1−xoutMnxout Te. The exciton bound polaron is computed for 0 ≤ x ≤ 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.