The electronic band structure and optical properties of boron arsenide

We compute the electronic band structure and optical properties of boron arsenide using the relativistic quasiparticle self-consistent $GW$ approach, including electron-hole interactions through solution of the Bethe-Salpeter equation. We also calculate its electronic and optical properties using standard and hybrid density functional theory. We demonstrate that the inclusion of self-consistency and vertex corrections provides substantial improvement in the calculated band features, in particular when comparing our results to previous calculations using the single-shot $GW$ approach and various DFT methods, from which a considerable scatter in the calculated indirect and direct band gaps has been observed. We find that BAs has an indirect gap of 1.674 eV and a direct gap of 3.990 eV, consistent with experiment and other comparable computational studies. Hybrid DFT reproduces the indirect gap well, but provides less accurate values for other band features, including spin-orbit splittings. Our computed Born effective charges and dielectric constants confirm the unusually covalent bonding characteristics of this III-V system.Comment: 7 pages, 3 figure

Self-regulation mechanism for charged point defects in hybrid halide perovskites

Hybrid halide perovskites such as methylammonium lead iodide (CH3NH3PbI3) exhibit unusually low free carrier concentrations despite being processed at low-temperatures from solution. We demonstrate, through quantum mechanical calculations, that the origin of this phenomenon is a prevalence of ionic over electronic disorder in stoichiometric materials. Schottky defect formation provides a mechanism to self-regulate the concentration of charge carriers through ionic compensation of charged point defects. The equilibrium charged vacancy concentration is predicted to exceed 0.4% at room temperature. This behaviour, which goes against established defect conventions for inorganic semiconductors, has implications for photovoltaic performance

Interface stoichiometry control to improve device voltage and modify band alignment in ZnO/Cu_2O heterojunction solar cells

The interface stoichiometry of cuprous oxide (Cu_2O) was controlled by adjusting the O_2 and Zn partial pressures during ZnO sputter deposition and measured by high-resolution X-ray photoelectron spectroscopy of ultrathin (<3 nm) ZnO films on Cu_2O. Open-circuit voltage measurements for ZnO/Cu_2O heterojunctions under AM1.5 illumination were measured and it was found that a stoichiometric interface can achieve the voltage entitlement dictated by the band alignment, whereas the non-stoichiometric interface showed large open-circuit voltage deficits. These results highlight not only the need for stoichiometric interfaces in Cu_2O devices, but also a reproducible experimental method for achieving stoichiometric interfaces that could be applied to any potential heterojunction partner. Additionally, valence-band offset measurements indicated changing the interface stoichiometry shifted the band alignment between Cu_2O and ZnO, which accounts for the variation in previously reported band offset values

New Insights into the Intrinsic Transport Properties of Sb 2 O 5 and ZnSb 2 O 6

Transparent conducting oxides are indispensable in a wide range of technological applications. However, materials that effectively combine high transparency with excellent carrier conductivity remain limited, with the field primarily relying on a few well‐established systems, such as indium tin oxide (ITO) and aluminum‐doped zinc oxide (AZO). Recently, Sb(V) oxides have emerged as a promising alternative class of materials, with the potential to compete with these state‐of‐the‐art oxides. Herein, Sb2O5 and ZnSb2O6 are examined using an advanced carrier transport approach based on the exact solution of the Boltzmann transport equation for the electron–phonon scattering. This approach not only reinforces the potential of Sb(V) oxides but also provides deeper insights into the electron–phonon scattering mechanisms in these materials

Heterostructures of GaN with SiC and ZnO enhance carrier stability and separation in framework semiconductors

A computational approach, using the density functional theory, is employed to describe the enhanced electron-hole stability and separation in a novel class of semiconducting composite materials, with the so-called double bubble structural motif, which can be used for photocatalytic applications. We examine the double bubble containing SiC mixed with either GaN or ZnO, as well as related motifs that prove to have low formation energies. We find that a 24-atom SiC sodalite cage inside a 96-atom ZnO cage possesses electronic properties that make this material suitable for solar radiation absorption applications. Surprisingly stable, the inverse structure, with ZnO inside SiC, was found to show a large deformation of the double bubble and a strong localisation of the photo-excited electron charge carriers, with the lowest band gap of ca. 2.15 eV of the composite materials considered. The nanoporous nature of these materials could indicate their suitability for thermoelectric applications

The adsorption of Cu on the CeO2(110) surface

We report a detailed density functional theory (DFT) study in conjunction with extended X-ray absorption fine structure (EXAFS) experiments on the geometrical and local electronic properties of Cu adatoms and Cu(II) ions in presence of water molecules and of CuO nanoclusters on the CeO2(110) surface. Our study of (CuO)n(=1,2&4) clusters on CeO2(110) shows that based on the Cu–O environment, the geometrical properties of these clusters may vary and their presence may lead to relatively high localization of charge on the exposed surfaces. We find that in the presence of an optimum concentration of water molecules, Cu has a square pyramidal geometry, which agrees well with our experimental findings; we also find that Cu(II) facilitates water adsorption on the CeO2(110) surface. We further show that a critical concentration of water molecules is required for the hydrolysis of water on Cu(OH)2/CeO2(110) and on pristine CeO2(110) surfaces

Valence band modification of Cr2O3 by Ni-doping: creating a high figure of merit p-type TCO

p-Type transparent conductors and semiconductors still suffer from remarkably low performance compared to their more widespread n-type counterparts, despite extensive investigation into their development. In this contribution, we present a comparative study on the defect chemistry of potential p-type transparent conducting oxides Mg-doped and Ni-doped Cr 2 O 3 . Conductivities as high as 28 S cm -1 were achieved by Ni-doping. By benchmarking crystallography and spectroscopy characterization against density functional theory calculations, we show that the incorporation of Ni into Cr 2 O 3 contributes to the composition of the valence band, making the formed holes more delocalized, while Mg states do not interact with the valence band in Mg-doped Cr 2 O 3 . Furthermore, it is experimentally proven that Ni has a higher solubility in Cr 2 O 3 than Mg, at least in the highly non-thermodynamic deposition conditions used for these experiments, which directly translates into a higher acceptor concentration. The combination of these two effects means that Ni is a more effective acceptor in Cr 2 O 3 than Mg and explains the improved conductivity observed for the former

Growth and properties of GaSbBi alloys

Molecular-beam epitaxy has been used to grow GaSb 1− x Bi x alloys with x up to 0.05. The Bi content, lattice expansion, and film thickness were determined by Rutherford backscattering and x-ray diffraction, which also indicate high crystallinity and that >98% of the Bi atoms are substitutional. The observed Bi-induced lattice dilation is consistent with density functional theory calculations. Optical absorption measurements and valence band anticrossing modeling indicate that the room temperature band gap varies from 720 meV for GaSb to 540 meV for GaSb 0.95Bi0.05, corresponding to a reduction of 36 meV/%Bi or 210 meV per 0.01 Å change in lattice constant