Controllable electron g-factors in HgMnTe quantum spheres

The electronic structure and Lande electron g-factors of manganese-doped HgTe quantum spheres are investigated, in the framework of the eight-band effective-mass model and the mean-field approximation. It is found that the electronic structure evolves continuously from the zero-gap configuration to an open-gap configuration with decreasing radius. The size dependence of electron g-factors is calculated with different Mn-doped effective concentration, magnetic field, and temperature values, respectively. It is found that the variations of electron g-factors are quite different for small and large quantum spheres, due to the strong exchange-induced interaction and spin-orbit coupling in the narrow-gap DMS nanocrystals. The electron g-factors are zero at a critical point of spherical radius R-c; however, by modulating the nanocrystal size their absolute values can be turned to be even 400 times larger than those in undoped cases. Copyright (c) EPLA, 2008.

Rashba spin splitting of the minibands of coupled InAs/GaAs pyramid quantum dots

The Rashba spin splitting of the minibands of coupled InAs/GaAs pyramid quantum dots is investigated using the k center dot p method and valence force field model. The Rashba splitting of the two dimensional miniband in the lateral directions is found due to the structure inversion asymmetry in the vertical direction while the miniband in the vertical direction has no Rashba spin splitting. As the space between dots increases, the Rashba coefficients decrease and the conduction-band effective mass increases. This Rashba spin splitting of the minibands will significantly affect the spin transport properties between quantum dots. (C) 2008 American Institute of Physics.

Transmission properties of electron in quantum rings

We investigated the transmission probability of a single electron transmission through a quantum ring device based on the single-band effective mass approximation method and transfer matrix theory. The time-dependent Schrodinger equation is applied on a Gaussian wave packet passing through the quantum ring system. The electron tunneling resonance peaks split when the electron transmits through a double quantum ring. The splitting energy increases as the distance between the two quantum rings decreases. We studied the tunneling time through the single electron transmission quantum ring from the temporal evolution of the Gaussian wave packet. The electron probability density is sensitive to the thickness of the barrier between the two quantum rings. (C) 2008 American Institute of Physics.

Electronic structure of a hydrogenic acceptor impurity in semiconductor nano-structures

The electronic structure and binding energy of a hydrogenic acceptor impurity in 2, 1, and 0-dimensional semiconductor nano-structures (i.e. quantum well (QW), quantum well wire (QWW), and quantum dot (QD)) are studied in the framework of effective-mass envelope-function theory. The results show that (1) the energy levels monotonically decrease as the quantum confinement sizes increase; (2) the impurity energy levels decrease more slowly for QWWs and QDs as their sizes increase than for QWs; (3) the changes of the acceptor binding energies are very complex as the quantum confinement size increases; (4) the binding energies monotonically decrease as the acceptor moves away from the nano-structures' center; (5) as the symmetry decreases, the degeneracy is lifted, and the first binding energy level in the QD splits into two branches. Our calculated results are useful for the application of semiconductor nano-structures in electronic and photoelectric devices.

Electronic structure in GaAs/AlxGa1-xAs spherical quantum dots

In this paper, how the dots' radius, At concentration and external electric field affect the single electron energy states in GaAs/AlxGa1-xAs spherical quantum dots are discussed in detail. Furthermore, the modification of the energy states is calculated when the difference in effective electron mass in GaAs and AlxGa1-xAs are considered. In addition, both the analytical method and the plane wave method are used in calculation and the results are compared, showing that they are in good agreement with each other. The results and methods can provide useful information for the future research and potential applications of quantum dots.

Spin-orbit splitting of a hydrogenic donor impurity in GaAs/GaAlAs quantum wells

The electronic states of a hydrogenic donor impurity in GaAs/GaAlAs quantum wells are investigated theoretically in the framework of effective-mass envelope function theory, including the effect of Rashba spin-orbit coupling. The splits of electron energy levels are calculated. The results show that (1) the split energy of the excited state is larger than that of the ground state; (2) the split energy peak appears as the GaAs well width increases from zero; and (3) the maximum split energy reaches about 1.6 meV. Our results are useful for the application of Rashba spin-orbit coupling to photoelectric devices. (c) 2008 American Institute of Physics.

Excitonic bright-to-dark transition induced by spin-orbit coupling

The center-of-mass motion of quasi-two-dimensional excitons with spin-orbit coupling is calculated within the framework of effective mass theory. The results indicate that the spin-orbit coupling will induce a controllable bright-to-dark transition in a quasi-two-dimensional exciton system. This procedure can work as a way to increase the lifetime of excitons. (c) 2008 American Institute of Physics.

Electronic structure and exciton states in the freestanding ZnO nanorods

The electronic structure and exciton states of cylindrical ZnO nanorods with radius from 2 to 6 nm are investigated based on the framework of the effective-mass theory. Using the adiabatic approximation, the exciton binding energies taking account of the dielectric mismatch are solved exactly when the total angular momentum of the exciton states L = 0 and L = +/- 1. We find that the exciton binding energies can be enhanced greatly by the dielectric mismatch and the calculated results are almost consistent with the experimental data. Meanwhile, we obtain the optical transition rule when the small spin-obit splitting Delta(so) of ZnO is neglected. Furthermore, the radiative lifetime and linear optical susceptibilities chi(w) of the exciton states are calculated theoretically. The theoretical results are consistent with the experimental data very well. (C) 2009 American Institute of Physics. [DOI 10.1063/1.3125456]

Strain Effects on the Optical Polarization Properties of R-Plane Wurtzite GaN

Using the effective-mass Hamiltonian for an arbitrary direction wurtzite semiconductor on the basis of k.p theory, we investigate the strain effects on the transition energies and optical properties in the R-plane ([1012]-oriented plane) GaN. The results show that (1) the transition energies decrease with the biaxial strains changing from -0.5 to 0.5%; and (2) giant optical anisotropy appears in the R-plane which is significantly affected by the biaxial strains. We clarify the relation between the strains and the polarization properties. Finally, we discuss the application of these properties to the R-plane GaN based devices. (c) 2009 The Japan Society of Applied Physics

Energy Levels of Hydrogenic Impurities in InAs Quantum Ring

The distribution of energy levels of the ground state and the low-lying excited states of hydrogenic impurities in InAs quantum ring was investigated by applying the effective mass approximation and the perturbation method. In 2D polar coordinates, the exact solution to the Schrodinger equation was used to calculate the perturbation integral in a parabolic confinement potential. The numerical results show that the energy levels of electron are sensitively dependent on the radius of the quantum ring and a minimum exists on account of the parabolic confinement potential. With decreasing the radius, the energy spacing between energy levels increases. The degenerate energy levels of the first excited state for hydrogenic impurities are not relieved, and when the degenerate energy levels are split and the energy spacing will increase with the increase in the radius. The energy spacing between energy levels of electron is also sensitively dependent on the angular frequency and will increase with the increases in it. The degenerate energy levels of the first excited state are not relieved. The degenerate energy levels of the second excited state are relieved partially. The change in angular frequency will have a profound effect upon the calculation of the energy levels of the ground state and the low-lying excited states of hydrogenic impurities in InAs quantum ring. The conclusions of this paper will provide important guidance to investigating the optical transitions and spectral structures in quantum ring.

Investigation of Electronic Energy Levels in InAs Quantum Dot with Shape of Lens by Using B-Spline Technique

The dependence of the electronic energy levels on the size of quantum dots (QDs) with the shape of spherical lens is studied by using the B-spline technique for the first time. Within the framework of the effective-mass theory, the values of electronic energy levels are obtained as a function of the height, radius and volume of QDs, respectively. When the height or radius of QDs increases, all the electronic energy levels lower, and the separations between the energy levels decrease. For lens-shape QDs, height is the key factor in dominating the energy levels comparing with the effect of radius, especially in dominating the ground-state level. These computational results are compared with that of other theoretical calculation ways. The B-spline technique is proved to be an effective way in calculating the electronic structure in QDs with the shape of spherical lens.

The electronic structure of strained ZnO/MgxZn1-xO superlattices and the influence of polarization

Based on the effective-mass model, the lower energies of the electron and the hole of ZnO/MgxZn1-xO superlattices are calculated. Because of the mismatch of the lattice constant between the ZnO well and the MgxZn1-xO barrier, piezoelectric and spontaneous polarization exist in ZnO/MgxZn1-xO superlattices and a macroscopical internal electric held is found when well width L-w >4 nm and Mg concentration x > 0.2. The parameters of ZnO/MgxZn1-xO superlattices such as lattice constant, band offset, etc. are also proposed. Through calculations, we found the internal electric field can change the lowest energies of the electron and hole to 105.4 and 85.1 meV when well width L-w up to 70 angstrom, which will influence the electronic and optical properties of ZnO/MgxZn1-xO superlattices greatly, while the Rashba effect from the internal electric field is so small that it can be neglected. The ground state exciton energies with different Mg concentration x are also calculated by variational method, our results are very close to the experimental results when Mg concentration x <= 0.3. (C) 2008 Elsevier B.V. All rights reserved.

Linear Rashba Model of a Hydrogenic Donor Impurity in GaAs/GaAlAs Quantum Wells

The Rashba spin-orbit splitting of a hydrogenic donor impurity in GaAs/GaAlAs quantum wells is investigated theoretically in the framework of effective-mass envelope function theory. The Rashba effect near the interface between GaAs and GaAlAs is assumed to be a linear relation with the distance from the quantum well side. We find that the splitting energy of the excited state is larger and less dependent on the position of the impurity than that of the ground state. Our results are useful for the application of Rashba spin-orbit coupling to photoelectric devices.

Symmetry and optical transition rule for low-dimensional semiconductor system with spin-orbit interaction and magnetic field

Starting from effective mass Hamiltonian, we systematically investigate the symmetry of low-dimensional structures with spin-orbit interaction and transverse magnetic field. The position-dependent potentials are assumed to be space symmetric, which is ever-present in theory and experiment research. By group theory, we analyze degeneracy in different cases. Spin-orbit interaction makes the transition between Zeeman sub-levels possible, which is originally forbidden within dipole approximation. However, a transition rule given in this paper for the first time shows that the transition between some levels is forbidden for space symmetric potentials. (C) 2009 Elsevier Ltd. All rights reserved.

Binding Energy and Spin-Orbit Splitting of a Hydrogenic Donor Impurity in AlGaN/GaN Triangle-Shaped Potential Quantum Well

In the framework of effective-mass envelope function theory, including the effect of Rashba spin-orbit coupling, the binding energy E-b and spin-orbit split energy Gamma of the ground state of a hydrogenic donor impurity in AlGaN/GaN triangle-shaped potential heterointerface are calculated. We find that with the electric field of the heterojunction increasing, (1) the effective width of quantum well (W) over bar decreases and (2) the binding energy increases monotonously, and in the mean time, (3) the spin-orbit split energy Gamma decreases drastically. (4) The maximum of Gamma is 1.22 meV when the electric field of heterointerface is 1 MV/cm.