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The electronic structure and Zeeman splittings of wurtzite Cd1-xMnxSe quantum spheres are studied using the k center dot p method and mean-field model. It is interesting to find that the Zeeman splittings of some hole states in quantum spheres are highly anisotropic due to the spin-orbit coupling and wurtzite crystal structure. The anisotropy of the Zeeman splittings of hole ground states in large dots is large, while that in small dot is small because the hole ground states vary with radius. An external electrical field can change the Zeeman splitting significantly, and tune the g factor from nearly 0 to about 100.

The electronic structures of N quantum dot molecules (QDMs) are investigated theoretically in the framework of effective-mass envelope function theory. The electron and hole energy levels are calculated. In the calculations, the effects of finite offset and valence-band mixing are taken into account. The theoretical method can be used to calculate the electronic structures of any QDM. The results show that (1) electronic energy levels decrease monotonically and the energy difference between the N QDMs decreases as the quantum dot (QD) radius increases; (2) the electron energy level is lower and quantum confinement is smaller for the larger N QDM; (3) the hole ground state energy level is lower for the one dot QDM than N (greater 1) QDMs if the QD radius is larger than about 5nm due to the valence-band mixing. The results are useful for the application of the N QDM to photoelectric devices.

Using the first-principles band-structure method and the special quasirandom structures approach, the authors have investigated the band structure of random AlxInyGa1-x-yN quaternary alloys. They show that the wave functions of the band edge states are more localized on the InN sites. Consequently, the photoluminescence transition intensity in the alloy is higher than that in GaN. The valence band maximum state of the quaternary alloy is also higher than GaN with the same band gap, indicating that the alloy can be doped more easily as p-type. (c) 2007 American Institute of Physics.

The Curie temperature of diluted magnetic semiconductor (DMS) nanowires and nanoslabs is investigated using the mean-field model. The Curie temperature in DMS nanowires can be much larger than that in corresponding bulk material due to the density of states of one-dimensional quantum wires, and when only one conduction subband is filled, the Curie temperature is inversely proportional to the carrier density. The T-C in DMS nanoslabs is dependent on the carrier density through the number of the occupied subbands. A transverse electric field can change the DMS nanowires from the paramagnet to ferromagnet, or vice versae. (c) 2007 American Institute of Physics.

The electronic structures and electron g factors of InSb1-sNs and GaAs1-sNs nanowires and bulk material under the magnetic and electric fields are investigated by using the ten-band k.p model. The nitrogen doping has direct and indirect effects on the g factors. A giant g factor with absolute value larger than 900 is found in InSb1-sNs bulk material. A transverse electric field can increase the g factors, which has obviously asymmetric effects on the g factors in different directions. An electric field tunable zero g factor is found in GaAs1-sNs nanowires. (C) 2007 American Institute of Physics.

The atomistic pseudopotential quantum mechanical calculations for million atom nanosized metal-oxide-semiconductor field-effect transistors (MOSFETs) are presented. When compared with semiclassical Thomas-Fermi simulation results, there are significant differences in I-V curve, electron threshold voltage, and gate capacitance. In many aspects, the quantum mechanical effects exacerbate the problems encountered during device minimization, and it also presents different mechanisms in controlling the behaviors of a nanometer device than the classical one.

We calculate the electronic structures and binding energy of a hydrogenic impurity in a hierarchically self-assembled GaAs/AlxGa1-xAs quantum dot (QD) in the framework of effective-mass envelope-function theory. The variation of the electronic structures and binding energy with the QD structure parameters and the position of the impurity are studied in detail. We find that (1) acceptor impurity energy levels depend more sensitively on the size of the QD than those of a donor impurity; (2) all impurity energy levels strongly depend on the GaAs quantum well (QW) width; (3) a donor impurity in the QD has only one binding energy level except when the GaAs QW is large; (4) an acceptor impurity in the QD has two binding energy levels, which correspond to heavy- and light-hole quantum states; (5) the binding energy has a maximum value when the impurity is located below the symmetry axis along the growth direction; and (6) the binding energy has a minimum value when the impurity is located at the top corner of the QD. (c) 2006 American Institute of Physics.

By comparing the results of some well-controlled calculation methods, we analyze the relative importance of bulk band structure, multi-bulk-band coupling, and boundary conditions in determining colloidal quantum dot conduction band eigenenergies. We find that while the bulk band structure and correct boundary conditions are important, the effects of multi-bulk-band coupling are small.

The band structures of wurtzite ZnO are calculated by the empirical pseudopotential method EPM . The eight parameters of the Zn and O atomic pseudopotential form factors are obtained with the formula of Schluter et al. Phys. Rev. B 12, 4200 1975 . The band parameters are extracted by using a k· p Hamiltonian to fit the EPM results. The calculated band-edge energies Eg, EA, EB, and EC at the point are in good agreement with the experimental results. Based on the band parameters obtained, valence subbands of wurtzite ZnO/MgxZn1−xO tensile-strained quantum wells with different well widths and Mg compositions are calculated by the six-band k· p method. Published version

Quantum-confined Stark effects in GaAs∕AlxGa1−xAs self-assembled quantum dots are investigated theoretically in the framework of effective-mass envelope function theory. The electron and hole energy levels and optical transition energies are calculated in the presence of an electric field in different directions. In our calculation, the effect of finite offset, valence-band mixing, the effects due to the different effective masses of electrons and holes in different regions, and the real quantum dot structures are all taken into account. The results show that the electron and hole energy levels and the optical transition energies can cause blueshifts when the electric field is applied along the opposite to the growth direction. Our calculated results are useful for the application of hierarchical self-assembly of GaAs∕AlxGa1−xAs quantum dots to photoelectric devices.

The transmission through coupled quantum dots (CQDs) is calculated using the coupled-channel recursion method. Our results reveal that the conductance peaks move to high energy as the CQDs radius decreases or the period increases. If we increase the transverse momentum the conductance peaks move to high energy. Applying this characteristic, we can design a switch device using CQDs by applying a static electric field perpendicular to transmission direction. The theoretical results qualitatively agree with the available experimental data. Our calculated results may be useful for the application of CQDs to photoelectric devices.

In the framework of the effective-mass envelope-function theory, the electronic and optical properties of a spherical core-shell quantum-dot quantum well (QDQW) structure with one and two wells have been investigated. The results show that the energies of electron and hole states depend sensitively on the well thickness and core radius of quantum-dot quantum well structure. An interesting spatially separated characteristic of electron and hole in QDQW is found and enhanced significantly in the two-wells case. The normalized oscillator strength for the optical transition between the electron and hole states in QDQW exhibits a deep valley at some special well thickness. The Coulomb interaction between the electron and hole is also taken into account. [S0163-1829(98)02412-6].

The pseudopotential method is used to calculate the electronic structures of long-period narrow-gap InAs-GaSb and HgTe-CdTe superlattices. The variations of the energy gaps with the layer thicknesses and the band offsets, the subband dispersion along the ${k}_{x}$ direction, the charge distributions along the lines connecting atoms in the [011] direction, and the optical-transition matrix elements are obtained. It is found that the crossing of the lowest electronic level and the highest hole level for the superlattice (InAs${)}_{\mathrm{n}}$(GaSb${)}_{\mathrm{n}}$ occurs at the period of 160 A\r{}. The band offset has an essential effect on the energy gaps of the superlattice (HgTe${)}_{\mathrm{n}}$(CdTe${)}_{\mathrm{n}}$ with longer periods. The behavior of the interface states in the HgTe-CdTe superlattice is also discussed.

The s-, ${p}_{0}$-, and ${p}_{\ifmmode\pm\else\textpm\fi{}}$-like ground and excited states of anisotropic donors in quantum wells are calculated with a linear combination of Gaussian orbitals with different exponents in the z direction and xy plane. The energies and wave functions of the ground and excited states can be obtained simultaneously by this method. In the case of anisotropic donors in the bulk materials and isotropic donors in the quantum wells our results are in agreement with previous theoretical results. In some cases our results are better. Using this method we calculate the variation of the anisotropic donor energies with well widths, anisotropic factors \ensuremath{\gamma}, and impurity positions in the quantum well. The energies of s-like donor states related to the second subband are also calculated. Finally, the donors of the X band edge in Si/Si-Ge quantum wells are discussed.

A method of studying the hole resonant tunneling in quantum wells is proposed. Because of the band-mixing effect at ${\mathit{k}}_{\mathrm{\ensuremath{\parallel}}}$\ensuremath{\ne}0,, the heavy and light holes can transform into each other in the process of tunneling. The transmission coefficients including h-h (heavy to heavy hole), h-l (heavy to light hole), l-l (light to light hole), and l-h are calculated as functions of hole energies, parallel wave vectors ${\mathit{k}}_{\mathrm{\ensuremath{\parallel}}}$, and electric-field bias. The resonant energies are consistent with the energies of bound states in the same quantum well. After the difference in the effective-mass parameters in the two materials is taken into account, the theoretical results are in agreement with those of the experiments. The theoretical method developed in the paper is applicable to the study of various kinds of tunneling transmission and subband structure problems in superlattices.

The electronic structures of superlattices under an in-plane magnetic field are studied by the method of expansion with sine functions. The electronic and hole magnetic energy levels are obtained as functions of kx,ky and the intensity of the magnetic field. The density of states and the magnetic-optical transition matrix elements are discussed. The variations of the binding energy of the heavy- and light-hole magnetic excitons with the magnetic field and the well width are also obtained. Finally, the electronic energy levels in the magnetic field along an arbitrary direction in the yz plane are calculated. Published version

Les structures electroniques des puits quantiques de dimension nulle sont etudies a l'aide d'un modele spherique dans le cadre de la theorie de la masse effective. L'effet de melange des trous lourds et legers est pris en compte, et on obtient la classification de la symetrie et les niveaux d'energie des etats de trou. On calcule les energies des etats des donneurs et accepteurs

Silicon tips used as field emitters have dimensions that are within the quantum confinement regime. Therefore they can be considered as freestanding silicon tips. In this letter, a photoluminescence spectrum of a 100×100 array of silicon tips was taken at 10 K. Narrow ultraviolet luminescence peaks were observed. Using the empirical pseudopotential homojunction model, it is demonstrated that these luminescence peaks come from energy levels arising from quantum confinement. By fitting the theoretical result to the experimental result, we conclude that the luminescence peaks come from Si quantum tips of about 20 A in width and that they are covered by silicon dioxide.