Showing papers on "Potential well published in 1989"

Non-linear optical device

Abstract: A non-linear optical device for carrying out optical signal processing using a non-linear optical material having a biasing electric field perpendicularly applied to a semiconductor that is laminated to form a quantum well structure. A well layer of the quantum well structure has substantially the same thickness as the Bohr radius of an exciton, and the magnitude of the biasing electric field is selected so that the distance between centers of gravity of an electron and a hole, which constitute the exciton, is from a fraction of to substantially equal to the effective Bohr radius. The thickness and potential of a barrier layer of the quantum well structure is selected such that the increase in the width of the absorption peak of the exciton caused by ionization due to tunneling in the biasing electric field is smaller than the width of the absorption peak with no electric field, and the wavelength of light used to activate the device is selected such that the photon energy nω is substantially equal to or slightly smaller than Eex/2, where Eex is the energy generated by the exciton of the quantum well structure. That light is polarized, and its electric field vector has a component normal to the layer of the quantum well structure.

Optical Properties of CdZnS-ZnS Strained-Layer Superiattices

Abstract: The Cd 0.3 Zn 0.7 S-ZnS strained-layer superlattices has for the first time been fabricated on (100)GaAs substrates by a low-pressure MOCVD method. Exciton luminescence properties were investigated by the photoluminescence spectroscopies which show that the quantum confinement effect of excitons occurs in the CdZnS alloy layer. Temperature dependence of the exciton properties reveals a dominant scattering process which originates from exciton-phonon interaction(Γ 10 =68meV). Nevertheless, the large exciton binding energy of about 166meV makes it possible to produce the exciton peak at room temperature. The effect of external electric field on the exciton intensity and its peak position is found and is tentatively interpreted in terms of a quantum confined Stark effect.

Electron Energy Levels in a Quantum Well within an In-Plane Magnetic Field

Abstract: The exact eigenenergy spectrum of an electron is calculated in a quantum well within an in‐plane magnetic field. The numerical solutions for the excited energy states as well as the ground‐state energy are found for various quantum‐well widths and barrier heights. The cyclotron orbits are considerably affected by the quantum well. The energy levels higher than the potential height of the quantum well and the energy levels lower than the potential height of the quantum well show quite different behaviors. These are explained with the properties of the combined potential and the wave function inherent to the system.

Optical Nonlinearities and Femtosecond Dynamics of Quantum Confined CdSe Microcrystallites

Abstract: Pump-probe spectroscopic techniques with nanosecond pulses are used to investigate the size quantization effects in CdSe microcrystallites in glass matrices (quantum dots). Nonlinear properties of the transitions between quantum confined electron and hole states are reported for low temperatures and at room temperature. Femtosecond four-wave mixing and differential transmission spectroscopic techniques were also employed to study the excited state dynamics and relaxation times of the quantum dots. The homogeneous and inhomogeneous contributions to the lowest electronic transitions are measured by femtosecond spectral hole burning at various temperatures. The inhomogeneous linewidth is due to size and shape distribution of the crystallites. Our experiments indicate that the hole-width increases with increasing light intensity. The optical nonlinearities as a function of microcrystallite size were investigated using single beam saturation experiment for the three quantum confined samples. A simple absorption saturation model was used to analyze the data. The results indicate that the saturation intensity is larger for smaller semiconductor sizes. Therefore, the index change per unit of intensity, Δn/I which is proportional to (α-αB)/Is is larger for larger sizes. Here, Δn is the index change, α is the absorption at the peak of the transition, αB is the background absorption, and Is is the saturation intensity.

Exciton-phonon system in a polar semiconductor quantum well

Abstract: An intermediate-coupling exciton-phonon system allowing for the image potential in a polar semiconductor quantum well is studied for the first time. A double-time unitary transformation to the Hamiltonian of the system is carried out and the motion of the exciton in the z direction is studied in detail. The variation of the induced potential with the width of the well, the ground-state, and the first–excited-state energies of the exciton in the well for different widths of the well are calculated. The method used in this paper is suitable to both weak-coupling and intermediate-coupling exciton-phonon systems and the results are more accurate than those of a single-time unitary transformation which is only suitable to a weak-coupling exciton-phonon system.

Nonlinear optical properties of commercial and experimental semiconductor-doped glasses

Abstract: The nonlinear optical properties, more specifically the Kerr nonlinearity, of commercial semiconductor-doped glasses have been extensively studied. The nonlinear mechanism is mainly bulk-like since no sizeable quantum confinement effect was observed in these glasses. Quantum confinement is however clearly exhibited by experimental glasses containing smaller particles. For CdSSe, phonon broadening is observed to play an important role.

Deposition of a-Si: H/a-SiC: H Multilayer Film by Excimer Laser CVD

Abstract: The deposition of a-Si: H/a-SiC: H multilayer film by ArF excimer laser chemical vapor deposition has been demonstrated. Each layer thickness was determined from a reactant gas pressure and a laser irradiation time. The XPS spectrum of the multilayer films shows that the chemical component of each layer changes periodically with an Ar ion etching time and X-ray diffraction intensity of the films shows that the period is in good agreement with the value calculated from the deposition rate. The optical measurement of the films shows that the optical bandgap of the multilayer films increased with decreasing a-Si: H layer thickness. The result can be interpreted in terms of the electron quantum confinement effect in the band structure of an amorphous semiconductor.

Intermediate-coupling exciton in a quantum well

Abstract: The interaction expression of the surface-optical phonons with an electron (a hole) in a slab is extended to the case of a quantum well and the Hamiltonian H of the exciton-phonon system allowing for the Gabovish image potential is obtained for the first time A double-time unitary transformation to the Hamiltonian H is carried out to obtain the Hamiltonian Hex of the exciton in a quantum well, and the motion of the exciton in the z direction is discussed in detail The result obtained is suitable not only for a weak-coupling exciton system but also for an intermediate-coupling exciton system

Optical response of excitons in a single quantum well: Calculation of normal incidence reflectivity

Abstract: We consider the optical response of a realistic semiconductor quantum well, where the exciton polarizability is nonlocal and the confinement of the exciton wave functions is nonideal. Normal incidence reflectivity is calculated in the case of GaAs/Ga0.7 Al0.3 As single quantum well. No significant difference has been found in comparison with the numerical results obtained either by the local response calculation or by the ideal confinement approximation.