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