arXiv subjects

Mauricio A. Flores

Publications and source records attributed to Mauricio A. Flores.

5 recordsLinked to original sources

arXiv2018

On the accuracy of the HSE hybrid functional to describe many-electron interactions and charge localization in semiconductors

Hybrid functionals, which mix a fraction of Hartree-Fock (HF) 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 (DMC) 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 DMC results with those obtained with the HSE functional and find a good agreement between both methods for (SiV)$^-$ and (SiV)$^0$, whereas the correct description of 3C-SiC with an extra electron crucially depends on the amount of HF 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 against the many-body \emph{GW} approximation for the description of the position of the defect states in the band gap.

cond-mat.mtrl-sci↗

arXiv2018

Origin of the anomalous semiconducting behaviour in dense lithium

Experimentally, it is known that lithium undergoes a metal to semiconductor transition at about 80 GPA and a reentrant semiconductor to metal transition near 120 GPA. This unusual behaviour has been attributed to the formation of high-pressure electrides in the Li-\textit{Aba}2 phase. Using the accurate wave function based quantum Monte Carlo (DMC) method, we show that the valence charge distribution of the Li-\textit{Aba}2 phase is incompatible with an insulating or semiconducting ground state. At DMC level, the most stable phase at 100 GPA is an orthorhombic oP24 structure with Pbca symmetry whose valence charge density shows an electride paired distribution, in correspondence with the theoretical predictions of Neaton and Ashcroft [Nature 00, 141 (1999)]. Here, we propose the electride pairing in the oP24-(Pbca) phase as the origin of the semiconducting behaviour observed in diamond anvil cell experiments.

cond-mat.mtrl-sci↗

arXiv2017

Defect properties of Sn- and Ge-doped ZnTe: Suitability for intermediate-band solar cells

We investigate the electronic structure and defect properties of Sn- and Ge- doped ZnTe by first-principles calculations within the DFT+$GW$ formalism. We find that $(\text{Sn}_\text{Zn})$ and $(\text{Ge}_\text{Zn})$ introduce isolated energy levels deep in the band gap of ZnTe, derived from Sn-5s and Ge-4s states, respectively. Moreover, the incorporation of Sn and Ge on the Zn site is favored in p-type ZnTe, in both Zn-rich and Te-rich environments. The optical absorption spectra obtained by solving the Bethe-Salpeter equation reveals that sub-bandgap absorptance is greatly enhanced due to the formation of the intermediate band. Our results suggest that Sn- and Ge-doped ZnTe would be a suitable material for the development of intermediate-band solar cells, which have the potential to achieve efficiencies beyond the single-junction limit.

cond-mat.mtrl-sci↗

arXiv2017

Self-compensation in phosphorus-doped CdTe

We investigate the self-compensation mechanism in phosphorus-doped CdTe. The formation energies, charge transition levels, and defects states of several P-related point defects susceptible to cause self-compensation are addressed by first-principles calculations. Moreover, we assess the in uence of the spin-orbit coupling and supercell-size effects on the stability of AX centers donors, 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 (P$_\text{i}$) and find that the self-compensation mechanism is not due to the formation of AX centers. Under Te-rich growth conditions, (P$_\text{i}$) exhibits a formation energy lower than the substitutional acceptor (P$_\text{Te}$) 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 (P$_\text{Te}$-V$_\text{Te}$) complexes.

cond-mat.mtrl-sci↗

arXiv2016

First-principles DFT + GW study of the Te antisite in CdTe

Formation energies, charge transitions levels, and quasiparticle defect states of the tellurium antisite $(\text{Te}_\text{Cd})$ in CdTe are addressed within the DFT${0.05cm}+{0.05cm}$\emph{GW} formalism. We find that $(\text{Te}_\text{Cd})$ induces a (+2/0) deep level at 0.99 eV above the valence band maximum, exhibiting a negative-U effect. Moreover, the calculated zero-phonon line for the excited state of $(\text{Te}_\text{Cd})^0$ corresponds closely with the $\sim$1.1 eV band, visible in luminescence and absorption experiments. Our results differ from previous theoretical studies, mainly due to the well-known band gap error and the incorrect position of the band edges predicted by standard DFT calculations.

cond-mat.mtrl-sci↗