3,683 research outputs found
Dicke effect in a quantum wire with side-coupled quantum dots
A system of an array of side-coupled quantum-dots attached to a quantum wire
is studied theoretically. Transport through the quantum wire is investigated by
means of a noninteracting Anderson tunneling Hamiltonian. Analytical
expressions of the transmission probability and phase are given. The
transmission probability shows an energy spectrum with forbidden and allowed
bands that depends on the up-down asymmetry of the system. In up-down symmetry
only the gap survives, and in up-down asymmetry an allowed band is formed. We
show that the allowed band arises by the indirect coupling between the up and
down quantum dots. In addition, the band edges can be controlled by the degree
of asymmetry of the quantum dots. We discuss the analogy between this
phenomenon with the Dicke effect in optics.Comment: 11 pages, 5 figures. To appear in Physica
Tellurium vacancy in cadmium telluride revisited: size effects in the electronic properties
The quantum states and thermodynamical properties of the Te vacancy in CdTe
are addressed by first principles calculations, including the supercell size
and quasiparticle corrections. It is shown that the 64-atoms supercell
calculation is not suitable to model the band structure of the isolated Te
vacancy. This problem can be solved with a larger 216-atoms supercell, where
the band structure of the defect seems to be a perturbation of that of the
perfect crystal. It is interesting to note that the Te-vacancy formation energy
calculated with both supercell sizes are close in energy, which is attributed
to error cancelation. We also show that the interplay between supercell size
effects and the band gap underestimation of the generalized gradient
approximation strongly influences the predicted symmetry of some charge states.Comment: 9 pages, 7 figure
Energetics and Electronic Properties of Interstitial Chlorine in CdTe
Indexación: Scopus.We acknowledge support from Chilean funding agency FONDECYT under Grants No. 1170480 (W.O.) and 1171807 (E.M-P.). Powered@NLHPC: This research was partially supported by the supercomputing infrastructure of the NLHPC (ECM-02).The role of interstitial chlorine in the electronic properties of CdTe is addressed by density functional theory calculations including hybrid functionals and large unit cells. The stability and diffusion energy barriers of the impurity are analyzed as a function of the Fermi level position in the band gap. Chlorine is found to be stable in at least five interstitial sites with rather close formation energies, suggesting that they are all probable to be found. In p-type CdTe, the most stable sites are at the center of a CdTe bond and at a split-interstitial configuration, both acting as shallow donors. Whereas in n-type CdTe, it is found at the tetrahedral site surrounded by Cd hosts, acting as a shallow acceptor. We also find that chlorine can induce a deep acceptor level in the bandgap after binding with three Cd host atoms, which can explain the experimentally observed high resistivity in Cl-doped CdTe. The energy barriers for chlorine diffusion in both p-type and n-type CdTe are also discussed. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheimhttps://onlinelibrary.wiley.com/doi/full/10.1002/pssb.20180021
Non-Linear Effects in Resonant Tunneling; Bistabilities and Self-Sustained Oscillating Currents
We study non-linear phenomena in double barrier heterostructures. Systems in
3D under the effect of an external magnetic field along the current and 1D
systems are analyzed. Non-linearities are reflected in the I-V characteristic
curve as bistabilities, instabilities and time dependent oscillations of the
currents. The nature of the non-linear behavior depends upon the parameters
that define the system.Comment: 3 pages, 2 figures, accepted for publication in Superlattices and
Microstructure
Transport in random quantum dot superlattices
We present a novel model to calculate single-electron states in random
quantum dot superlattices made of wide-gap semiconductors. The source of
disorder comes from the random arrangement of the quantum dots (configurational
disorder) as well as spatial inhomogeneities of their shape (morphological
disorder). Both types of disorder break translational symmetry and prevent the
formation of minibands, as occurs in regimented arrays of quantum dots. The
model correctly describes channel mixing and broadening of allowed energy bands
due to elastic scattering by disorder
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