Electron-hole Transition Energies Research Articles

Uncorrelated electron-hole transition Energy in GaN│InGaN│GaN Spherical QDQW Nanoparticles

The electron (hole) energy and uncorrelated \(1S_e - 1S_{h}\) electron-hole transition in Core(GaN)| well(In\(_x\)Ga\(_{1 - x}\)N)| shell(GaN) spherical QDQW nanoparticles is investigated as a function of the inner and the outer radii. The calculations are performed within the framework of the effective-mass approximation and the finite parabolic potential confinement barrier in which two confined parameters are taking account. The Indium composition effect is also investigated. A critical value of the outer and the inner ratio is obtained which constitutes the turning point of two indium composition behaviors.

Electron–hole transition energy for a spherical quantum dot confined in a nano-cylindrical wire

A single-band constant confining potential is applied to InAs spherical quantum dot confined in a GaAs cylindrical nano-wire to determine the electronic structure. The energy eigenvalues and transition energies are numerically calculated as a function of the dot radius. The calculations were performed within the effective mass approximation, using the finite element method. The effect of both spherical and cylindrical confinement, the size dependence of the ground and first excited state energies for electron and heavy hole and transition energies are reported and compared with experimental and theoretical results in relevant conditions.

Modelling of the composition segregation effect during epitaxial growth of InGaAs quantum well heterostructures

Using a Monte Carlo (MC) technique, we performed numerical modelling of the kinetic segregation effect during epitaxial growth of a heterostructure containing an IncGa1−cAs quantum well (QW) surrounded by two GaAs barriers. The growth occurs in the direction coinciding with or slightly tilted from [0 0 1]. The model of growth kinetics takes into account the effect of pseudomorphic deformation of the underlying atomic layers onto the activation energy of adatom diffusion in the growing monolayer. It influences the surface segregation of In atoms and affects the QW shape. Within the effective mass approximation, the dependence of the lowest electron–hole transition energy on the degree of In/Ga segregation (in turn, depending upon the growth conditions and substrate tilting angle) was calculated. The calculations were performed using the composition profiles obtained from the MC modelling and taking into account the corresponding distribution of the elastic strain. The results show that the segregation effect leads to a considerable blue shift and broadening of the QW photoluminescence (PL) peak which increase for higher growth temperatures and lower values of the total cation flux from the gas phase onto the growing surface. Growth on vicinal substrates leads to a reduction of the PL peak broadening.

Effects of geometry, applied hydrostatic pressure and magnetic field on the electron–hole transition energy in a GaAs–Ga1−xAlxAs pillbox immersed in a system of Ga1−yAlyAs

In this work, we study the behavior of the electron–hole transition energy in a GaAs–Ga1−xAlxAs pillbox immersed in a system of Ga1−yAlyAs as a function of thickness of the ladder barrier potential for a fixed length of the pillbox, length of the pillbox, thickness of the ladder barriers and pillbox position in the host of Ga1−yAlyAs. The behavior of the electron–hole transition energy as a function of an applied hydrostatic pressure and an applied magnetic field is also studied. For both electron and hole we found that in the strong confinement regime (L⩽10Å) energy of the ground state as function of the position of the pillbox relative to the ladder barrier potential presents a behavior similar to the binding energy of a hydrogenic impurity in quantum wells, quantum wires and quantum dots [L. Esaki, R. Tsu, IBM J. Res. Dev. 14 (1970) 61; G. Bastard, Phys. Rev. B 24 (1981) 4714; N. Porras-Montenegro, J. López-Gondar, L.E. Oliveira, Phys. Rev. B 43 (1991) 1824]. Electron–heavy hole transition energies increase with the applied magnetic field. Also, we have found that these transition energies, as a function of the applied hydrostatic pressure, present an excellent agreement with experimental reports by Venkateswaran et al. [phys. Rev. B 33 (1986) 8416].

Hydrostatic‐pressure effects on the correlated electron–hole transition energies in GaAs–Ga1–xAlxAs semiconductor quantum wells

AbstractThe effects of hydrostatic pressure on the correlated e–h transition energies in single GaAs–Ga1–xAlxAs quantum wells are calculated via a variational procedure, in the framework of the effective‐mass and non‐degenerate parabolic‐band approximations. The valence‐band anisotropy is included in our theoretical model by using different hole masses in different spatial directions. Both heavy‐ and light‐hole exciton energies are obtained, and correlated e–h transition energies are found in good agreement with available experimental measurements. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Effects of applied magnetic fields and hydrostatic pressure on the optical transitions inself-assembled InAs/GaAs quantum dots

A theoretical study of the photoluminescence peak energies in InAs self-assembled quantumdots embedded in a GaAs matrix in the presence of magnetic fields applied perpendicularto the sample plane is performed. The effective mass approximation and a parabolicpotential cylinder-shaped model for the InAs quantum dots are used to describe theeffects of magnetic field and hydrostatic pressure on the correlated electron–holetransition energies. Theoretical results are found in quite good agreement withavailable experimental measurements for InAs/GaAs self-assembled quantum dots.

Correlated electron–hole transition energies in quantum-well wires: Effects of hydrostatic pressure

We perform a theoretical study, using a variational approach, of the effects of hydrostatic pressure on the exciton binding energies and photoluminescence peak positions in GaAs – Ga 1 - x Al x As cylindrical quantum-well wires within the effective-mass approximation. Calculated results suggest that future device applications may be realized by properly varying the wire dimensions and applying hydrostatic pressure.

Electron-hole transitions in self-assembled InAs/GaAs quantum dots: Effects of applied magnetic fields and hydrostatic pressure

A theoretical study of the effects of applied magnetic fields and hydrostatic pressure on the electron-hole transition energies in self-assembled InAs/GaAs quantum dots is presented. The effective-mass approximation and a model of a cylindrical-shaped quantum dot with in-plane parabolic potential have been used to describe the InAs/GaAs quantum dots. Present theoretical results are in quite good agreement with experimental measurements of the magnetic field and pressure dependence of the exciton transition energies in InAs/GaAs self-assembled quantum dots.

Vertical coupling effects and transition energies in multilayer InAs/GaAs quantum dots

Abstract We investigate the transition energy of vertically stacked semiconductor quantum dots with a complete three-dimensional (3D) model in an external magnetic field. In this study, the model formulation includes: (1) the position-dependent effective mass Hamiltonian in non-parabolic approximation for electrons, (2) the position-dependent effective mass Hamiltonian in parabolic approximation for holes, (3) the finite hard-wall confinement potential, and (4) the Ben Daniel–Duke boundary conditions. To solve the nonlinear problem, a nonlinear iterative method is implemented in our 3D nanostructure simulator. For multilayer small InAs/GaAs quantum dots, we find that the electron–hole transition energy is dominated by the number of stacked layers. The inter-distance d plays a crucial role in the tunable states of the quantum dots. Under zero magnetic field for a 10-layer QDs structure with d =1.0 nm, there is about 30% variation in the electron ground state energy. Dependence of the magnetic field on the electron–hole transition energy is weakened when the number of stacked layers is increased. Our investigation is constructive in studying the magneto-optical phenomena and quantum optical structures.

Electron Transition Energy for Vertically Coupled InAs/GaAs Semiconductor Quantum Dots and Rings

We investigate the transition energy of vertically coupled quantum dots and rings (VCQDs and VCQRs) with a three-dimensional (3D) model under an applied magnetic field. The model formulation includes (1) the position-dependent effective mass Hamiltonian in the nonparabolic approximation for electrons, (2) the position-dependent effective mass Hamiltonian in the parabolic approximation for holes, (3) the finite hard-wall confinement potential, and (4) the Ben Daniel-Duke boundary conditions. We explore small VCQDs and VCQRs with disk (DI) and conical (CO) shapes. For small VCQDs and VCQRs, the electron-hole transition energy is dominated by the interdistance d which plays a crucial role in the tunable states of structures. Under zero magnetic field, there is about 25% variation in the electron ground state energy for both InAs/GaAs DI-shaped VCQDs and VCQRs with d varying from 0.4 nm to 4.8 nm. The energy spectra of the CO-shaped VCQDs are the most stable against the structure interdistance deviations (among dots and rings of the same volume). For a fixed d, VCQDs show diamagnetic shift; contrarily, VCQRs imply a nonperiodical transition among the lowest electron energy states. The energy band gap of VCQRs oscillates nonperiodically between the lowest electron and holes states as a function of external magnetic fields. Our investigation is constructive for studying the magneto-optical phenomena of the nanoscale semiconductor artificial molecules.

Numerical Calculation of Electronic Structure for Three-Dimensional Nanoscale Semiconductor Quantum Dots and Rings

In this paper the electronic structure of nanoscale ellipsoid-torus-shaped semiconductor quantum dot and quantum ring is investigated of utilizing a unified model. This three-dimensional model considers the effective one-band Hamiltonian, the position- and energy-dependent effective mass approximation and Lande factor, the finite hard wall confinement potential, and the Ben Daniel-Duke boundary conditions. It is solved numerically without any fitting parameters by using a computationally cost effective nonlinear iterative method. It is found that the penetration of magnetic fields into non-simply connected topology of structures leads to substantial difference in the transition energy between InAs/GaAs quantum dot and quantum ring. The quantum ring exhibits non-periodical electron-hole transition energies when the magnetic field increases. Contrary to the one-dimensional periodical argument on the ring's energy spectra, our examination into the nanoscale semiconductor quantum ring agrees with the experimental result. The energy band gap of quantum dot is an increasing function of the magnetic field. For quantum rings the energy band gap oscillates non-periodically and the oscillation period is strongly controlled by the inner radius of structures. The magnetization of quantum ring not only jumps non-periodically but also saturates eventually when the magnetic field increases.

Study of the effects of size quantization in coupled AlxGa1−x As/GaAs/Alx Ga1−x as quantum wells by means of photoreflectance spectroscopy

Photoreflectance spectra are measured in heterostructures with coupled quantum wells at room temperature. The energies of the optical transitions are determined, and their variation with the well width and barrier thickness is studied. The experimental results are compared with the theoretically calculated electron-hole transition energies. Good agreement is obtained for narrow wells.

Stark localization in superlattices: Comparison of an empirical two-band model with experiment.

We have measured the electron-hole transition energies in a strongly coupled GaAs/${\mathrm{Al}}_{0.3}$${\mathrm{Ga}}_{0.7}$As superlattice in an electric field. The results of these measurements are compared with calculations based on an empirical two-band model, including excitonic effects. Excellent agreement is obtained between theory and experiment with no adjustments to the parameters in the calculations. This comparison provides a stringent test of the theory and shows that simple envelope-function formalisms are capable of accurate predictions of the optical properties of superlattices with thin (\ensuremath{\sim}20 \AA{}) layers.

Electron-hole transition energies and atomic steps at the interfaces of thin InGaAs/InP quantum wells

We measure the absorption of thin InGaAs/InP quantum wells with a well width between 0 and 20 Å. The discretization of the transition energies due to the quantization of the well width by monolayers is clearly observed for both the heavy and light hole excitons. The dependences of the heavy and light hole transition energies on the InGaAs growth time are investigated and show striking differences. This is discussed in relation to the atomic steps at the interfaces of the wells. The measured heavy and light hole transition energies agree well with calculation, which takes the split-off holes into account.