The electronic structure and the formation of polarons in Mo-doped BiVO4 measured by angle-resolved photoemission spectroscopy.

Mansour Mohamed,Christoph Janowitz,Mario Brützam,Matthias M May,Roel Van De Krol,Mattia Mulazzi,Reinhard Uecker,Michael Kanis

doi:10.1039/c9ra01092k

Abstract

We experimentally investigated the electronic structure of Mo-doped BiVO4 high-quality single-crystals with synchrotron radiation-excited angle-resolved photoelectron spectroscopy (ARPES). By photon-energy dependent ARPES, we measured the bulk-derived valence band dispersion along the direction normal to the (010) cleavage plane, while the dispersion along the in-plane directions is obtained by angle-dependent measurements at fixed photon energy. Our data show that the valence band has a width of about 4.75 eV and is composed of many peaks, the two most intense have energies in good agreement with the theoretically calculated ones. A non-dispersive feature is observed in the fundamental gap, which we attribute to quasiparticle excitations coupling electrons and phonons, i.e. polarons. The determination of the polaron peak binding energy and bulk band gap allows to fix the value of the theoretical mixing parameter necessary in hybrid Hartree–Fock calculations to reproduce the experimental data. The attribution of the in-gap peak to polarons is strengthened by our discussion in the context of experimental transport data and ab initio theory.

Highlights

Ternary metal-oxides are materials hosting a wide range of interesting properties, from either the fundamental or the applied point of view
We report on the experimental band structure of Mo-doped (1%) BiVO4 single-crystals measured by means of angle-resolved photoelectron spectroscopy (ARPES)
The appropriate determination of the Brillouin zone's (BZ) shape is important for the electronic structure investigation, in particular for monoclinic structures, since the shape of the BZ depends on the actual length of the lattice parameters.[23]

Summary

Introduction

Ternary metal-oxides are materials hosting a wide range of interesting properties, from either the fundamental or the applied point of view. The family of ruthenium oxides shows metallic magnetism and spin-triplet superconductivity, observed in SrRuO3 and Sr2RuO4, respectively.[1,2] Combining the Mott insulator LaAlO3 with the band insulator SrTiO3 in a heterostructure originates a two-dimensional electron gas[3] at the interface, in which ferromagnetic[4] and superconducting areas[5] coexist. Metal oxides are used as catalysts for solar water splitting applications[6] and the material we are reporting on, BiVO4, is a very prominent representative of complex metal oxide semiconductors. BiVO4 is typically operated as a photoanode in combination with a second absorber, such as a silicon photovoltaic cell.

Results

Discussion

Conclusion