Examinando por Autor "Orellana, W."

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    Accuracy of the Heyd-Scuseria-Ernzerhof hybrid functional to describe many-electron interactions and charge localization in semiconductors
    (American Physical Society, 2018-10) Flores, M.A.; Orellana, W.; Menéndez-Proupin, E.
    Hybrid functionals, which mix a fraction of Hartree-Fock exchange with local or semilocal exchange, have become increasingly popular in quantum chemistry and computational materials science. Here, we assess the accuracy of the Heyd-Scuseria-Ernzerhof (HSE) hybrid functional to describe many-electron interactions and charge localization in semiconductors. We perform diffusion quantum Monte Carlo calculations to obtain the accurate ground-state spin densities of the negatively charged (SiV)- and the neutral (SiV)0 silicon-vacancy center in diamond and of the cubic silicon carbide (3C-SiC) with an extra electron. We compare our diffusion quantum Monte Carlo results with those obtained with the HSE functional and find a good agreement between the two methods for (SiV)- and (SiV)0, whereas the correct description of 3C-SiC with an extra electron crucially depends on the amount of Hartree-Fock exchange included in the functional. Also, we examine the case of the neutral Cd vacancy in CdTe, for which we assess the performance of HSE versus the many-body GW approximation for the description of the position of the defect states in the band gap. © 2018 American Physical Society.
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    Energetics and Electronic Properties of Interstitial Chlorine in CdTe
    (Wiley-VCH Verlag, 2019-03) Orellana, W.; Menéndez-Proupin, E.; Flores, M.A.
    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 CdTe 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, Weinheim
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    Self-compensation in phosphorus-doped CdTe
    (American Physical Society, 2017) Flores, M.A.; Orellana, W.; Menéndez-Proupin, E.
    We investigate the self-compensation mechanism in phosphorus-doped CdTe. The formation energies, charge transition levels, and defect states of several P-related point defects susceptible to cause self-compensation are addressed by first-principles calculations. Moreover, we assess the influence of the spin-orbit coupling and supercell-size effects on the stability of AX centers, which are believed to be responsible for most of the self-compensation. We report an improved result for the lowest-energy configuration of the P interstitial (Pi) and find that the self-compensation mechanism is not due to the formation of AX centers. Under Te-rich growth conditions, (Pi) exhibits a formation energy lower than the substitutional acceptor (PTe) when the Fermi level is near the valence band, acting as compensating donor, while, for Cd-rich growth conditions, our results suggest that p-type doping is limited by the formation of (PTe-VTe) complexes.
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    Tellurium vacancy in cadmium telluride revisited: Size effects in the electronic properties
    (Wiley-VCH Verlag, 2015-12) Menéndez-Proupin, E.; Orellana, W.
    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. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.