Optical spectra of ZnO in the far ultraviolet: First-principles calculations and ellipsometric measurements

Gori, Paola; Rakel, M.; Cobet, Christoph; Richter, Wolfgang; Esser, N.; Hoffmann, A.; Sole, R. Del; Cricenti, A.; Pulci, Olivia

doi:10.1103/physrevb.81.125207

Cited by 51 publications

(46 citation statements)

References 62 publications

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“…In anisotropic bulks (WUR, BCT and h-BN), the ordinary (OC) and extraordinary (EC) components are given, associated to a momentum transfer parallel and perpendicular to the ab plane, respectively. In bulk WUR, the values found are in agreement with previous theoretical estimations at the same level of theory [54][55][56] , and close to the experimental value of 3.7 57 , a typical value for a semiconductor of mixed ionic and covalent character. Among the polymorphs, the variations of ∞ qualitatively correlate with the mean valence electronic density n, as expected from simple models of screening…”

Section: A Optical Dielectric Functionsupporting

confidence: 91%

Confinement effects in ultrathin ZnO polymorph films: Electronic and optical properties

2016

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Relying on generalized-gradient and hybrid first-principles simulations, this work provides a complete characterization of the electronic properties of ZnO ultra-thin films, cut along the BodyCentered-Tetragonal(010), Cubane(100), h-BN(0001), Zinc-Blende(110), Wurtzite (1010) and (0001) orientations. The characteristics of the local densities of states are analyzed in terms of the reduction of the Madelung potential on under-coordinated atoms and surface states/resonances appearing at the top of the VB and bottom of the CB. The gap width in the films is found to be larger than in the corresponding bulks, which is assigned to quantum confinement effects. The components of the high frequency dielectric constant are determined and the absorption spectra of the films are computed. They display specific features just above the absorption threshold due to transitions from or to the surface resonances. This study provides a first understanding of finite size effects on the electronic properties of ZnO thin films and a benchmark which is expected to foster experimental characterization of ultra-thin films via spectroscopic techniques.

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Section: A Optical Dielectric Functionsupporting

confidence: 91%

Confinement effects in ultrathin ZnO polymorph films: Electronic and optical properties

2016

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“…Adoption of a better pseudopotential and basis set indeed partially corrected this discrepancy. Inclusion of semicore electrons in Zn has also been found to be crucial for obtaining reliable G 0 W 0 corrections over the PBE gap [107], similar to what was reported by Gori et al [108]. In conclusion, we believe that, given the above discussion, the agreement between our computed PW and LCAO band gaps should be deemed satisfactory.…”

Section: Dft Lda Gga and Standard Hybridssupporting

confidence: 87%

Electronic structure and phase stability of oxide semiconductors: Performance of dielectric-dependent hybrid functional DFT, benchmarked againstGWband structure calculations and experiments

et al. 2015

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We investigate band gaps, equilibrium structures, and phase stabilities of several bulk polymorphs of wide-gap oxide semiconductors ZnO, TiO 2 , ZrO 2 , and WO 3 . We are particularly concerned with assessing the performance of hybrid functionals built with the fraction of Hartree-Fock exact exchange obtained from the computed electronic dielectric constant of the material. We provide comparison with more standard density-functional theory and GW methods. We finally analyze the chemical reduction of TiO 2 into Ti 2 O 3 , involving a change in oxide stoichiometry. We show that the dielectric-dependent hybrid functional is generally good at reproducing both ground-state (lattice constants, phase stability sequences, and reaction energies) and excited-state (photoemission gaps) properties within a single, fully ab initio framework.

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“…It has been shown, however, that excluding s and p semicore electrons can lead to substantial errors in GW calculations, as observed for systems including elements such as Cd, 145,146 Zn, 147,148 Cu, 149 and Au. 136 The results of GW calculations turn out to be quite sensitive to the inclusion of incomplete semicore shells in the valence partition (ISSV), even in cases…”

Section: Resultsmentioning

confidence: 96%

Implementation and Validation of Fully RelativisticGWCalculations: Spin–Orbit Coupling in Molecules, Nanocrystals, and Solids

Scherpelz

Govoni

Hamada

et al. 2016

J. Chem. Theory Comput.

208

173

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We present an implementation of G0W0 calculations including spin-orbit coupling (SOC) enabling investigations of large systems, with thousands of electrons, and we discuss results for molecules, solids, and nanocrystals. Using a newly developed set of molecules with heavy elements (called GW-SOC81), we find that, when based upon hybrid density functional calculations, fully relativistic (FR) and scalar-relativistic (SR) G0W0 calculations of vertical ionization potentials both yield excellent performance compared to experiment, with errors below 1.9%. We demonstrate that while SR calculations have higher random errors, FR calculations systematically underestimate the VIP by 0.1 to 0.2 eV. We further verify that SOC effects may be well approximated at the FR density functional level and then added to SR G0W0 results for a broad class of systems. We also address the use of different root-finding algorithms for the G0W0 quasiparticle equation and the significant influence of including d electrons in the valence partition of the pseudopotential for G0W0 calculations. Finally, we present statistical analyses of our data, highlighting the importance of separating definitive improvements from those that may occur by chance due to a limited number of samples. We suggest the statistical analyses used here will be useful in the assessment of the accuracy of a large variety of electronic structure methods.

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Optical spectra of ZnO in the far ultraviolet: First-principles calculations and ellipsometric measurements

Cited by 51 publications

References 62 publications

Confinement effects in ultrathin ZnO polymorph films: Electronic and optical properties

Confinement effects in ultrathin ZnO polymorph films: Electronic and optical properties

Electronic structure and phase stability of oxide semiconductors: Performance of dielectric-dependent hybrid functional DFT, benchmarked againstGWband structure calculations and experiments

Implementation and Validation of Fully RelativisticGWCalculations: Spin–Orbit Coupling in Molecules, Nanocrystals, and Solids

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