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Zinc blende copper iodide, a p-type semiconductor that is transparent in the visible spectral range, has attracted growing attention as a promising material for transparent electronics. While the zinc blende γ-phase is the most studied, the semiconducting layered β-phase deserves more consideration being potentially suited for 2D applications. Here, we present an ab initio study of these two phases of CuI in the framework of density functional theory. We first discuss structural and elastic properties, and for β-CuI we calculate the exfoliation energy. The comparison of electronic band structures and optical properties shows that small light-hole effective masses and large band gaps are common characteristics of the two considered phases. These properties are also preserved in the β-CuI monolayer and point to the possibility of obtaining a high-performance transparent monolayer conductor for application in 2D electronics. [ABSTRACT FROM AUTHOR]

We present ab initio quasiparticle calculations for electronic excitations and the fundamental band gap of the strongly correlated transition-metal oxide CuO using the G W approximation of many-body perturbation theory. Problems related to the suitability of the method for strongly correlated materials and issues of self-consistency are addressed. We explain why quasiparticle self-consistent GW strongly overestimates the band gap of CuO. Apart from the band gap, electron addition and removal spectra in the quasiparticle approximation including lifetime and matrix-element effects are found to be in excellent agreement with the quasiparticle excitations in direct and inverse photoemission data. [ABSTRACT FROM AUTHOR]

While there is a persistent interest in oxides, e.g., for semiconductor technology or optoelectronics, it seems to be difficult to achieve n-type and p-type doping for one and the same material. At the same time, it is important to understand the electronic structure for both types of doping individually. In this work, we use modern electronic-structure calculations to compute the density of states as well as effective electron and hole masses for n-type (ZnO, CdO, SnO2) and p-type (MnO, NiO) oxide materials. We establish our ab initio electronic structures by comparison to photoemission experiments at various incident photon energies. Taking into account the photoionization cross-sections, we are able to analyze the contributions of different atomic states and to verify the results by comparison to measured data. Based on these electronic structures, we calculate free-electron and free-hole masses as well as their dependence on the concentration of free carriers in the system. For SnO2, we compare with experimental results from another article (see M. Feneberg et al., Phys. Status Solidi A, DOI 10.1002/pssa.201330147 (2013) ) in this special issue. [ABSTRACT FROM AUTHOR]

Electron doping turns semiconductors conductive even when they have wide fundamental band gaps. The degenerate electron gas in the lowest conduction-band states, e.g., of a transparent conducting oxide, drastically modifies the Coulomb interaction between the electrons and, hence, the optical properties close to the absorption edge. We describe these effects by developing an ab initio technique which captures also the Pauli blocking and the Fermi-edge singularity at the optical-absorption onset, that occur in addition to quasiparticle and excitonic effects. We answer the question whether free carriers induce an excitonic Mott transition or trigger the evolution of Wannier-Mott excitons into Mahan excitons. The prototypical n-type zinc oxide is studied as an example. [ABSTRACT FROM AUTHOR]

Isostructural and heterostructural pseudobinary MgxZn1-xO and CdxZn1-xO alloys are studied by combining the wurtzite and the rocksalt polymorphs within a cluster expansion. The computationally demanding calculation of the quasiparticle electronic structure has been achieved for all cluster cells of the expansion using the recently developed HSE03 + G0W0 scheme. These results are used to compute the configurational averages for the fundamental band gaps and the densities of states. A strongly nonlinear behavior of the band gaps is observed and it is quantified by means of the corresponding bowing parameters for both material systems. In order to calculate the macroscopic dielectric functions, including excitonic and local-field effects for iso- and heterostructural MgxZn1-xO alloys as well as wurtzite (wz) CdxZn1-xO, the Bethe-Salpeter equation has been solved for each of the corresponding clusters. The respective configurational averages indicate that the composition-dependent variation in the exciton peaks allows conclusions on the alloy composition and preparation conditions. [ABSTRACT FROM AUTHOR]

The study of the oxygen vacancy (F center) in MgO has been aggravated by the fact that the positively charged and the neutral vacancy (F+ and F0, respectively) absorb at practically identical energies. Here we apply many-body perturbation theory in the G0 W0 approximation and the Bethe-Salpeter approach to calculate the optical absorption and emission spectrum of the oxygen vacancy in all three charge states. We observe unprecedented agreement between the calculated and the experimental optical absorption spectra for the F0 and F+ center. Our calculations reveal that not only the absorption but also the emission spectra of different charge states peak at nearly the same energy, which leads to a reinterpretation of the F center's optical properties. [ABSTRACT FROM AUTHOR]