Modulation effect of low-electronegativity non-metallic elements on the electronic structure of group-IVB transition metal oxides

Abstract

Transparent conducting materials (TCMs) are widely used in many optoelectronic devices. Transition metal oxides account for a large proportion of transparent conducting materials (TCMs). However, some transition metal oxides with p-type TCMs characteristics usually hold large holes effective mass, the performance is not as good as n-type TCMs. The reason is that the VBM (maximum valence band) of most transition metal oxides is mainly composed of strongly localized O-2p orbitals. Reducing the localization degree of electrons in the VBM is the key to solving the problem. In order to study the modulation effect for the addition of nonmetal constituents with less electronegativity (such as S/Se/Te) on the VBM for transition metal oxides, we perform a systematic theoretical study of 12 kinds of MmXnYl (M = Ti, Zr, Hf and X, Y= O, S, Se, Te) based on density functional theory (DFT), including the structural, electronic, and optical properties. For the potential TCMs candidates (c-ZrOS, t-ZrOS, c-HfOS) that exhibit excellent conductivity and high transparency, the dynamic stability is studied through phonon spectra. For the transition metal compound with the same symmetry, a convenient method to compare the effective mass of holes and band gap is proposed, that is, a larger electronegativity of the entire compound usually means a larger band gap and effective mass of holes. The effective mass of electrons is primarily determined by the localization of the d-orbital of transition metal, the smaller the electronegativity of transition metals means the smaller effective mass of electrons and larger band gap.