Electronic properties of layered multicomponent wide-band-gap oxides: A combinatorial approach

Abstract

The structural, electronic, and optical properties of 12 multicomponent oxides with layered structure $RAM$O${}_{4}$, where $R$${}^{3+}$ = In or Sc, $A$${}^{3+}$ = Al or Ga, and $M$${}^{2+}$ = Ca, Cd, Mg, or Zn, are investigated using first-principles density functional approach. The compositional complexity of $RAM$O${}_{4}$ leads to a wide range of band-gap values varying from 2.45 eV for InGaCdO${}_{4}$ to 6.29 eV for ScAlMgO${}_{4}$ as obtained from our self-consistent screened-exchange local density approximation calculations. Strikingly, despite the different band gaps in the oxide constituents, namely, 2--4 eV in CdO, In${}_{2}$O${}_{3}$, or ZnO, 5--6 eV for Ga${}_{2}$O${}_{3}$ or Sc${}_{2}$O${}_{3}$, and 7--9 eV in CaO, MgO, or Al${}_{2}$O${}_{3}$, the bottom of the conduction band in the multicomponent oxides is formed from the $s$ states of all cations and their neighboring oxygen $p$ states. We show that the hybrid nature of the conduction band in multicomponent oxides originates from the unusual fivefold atomic coordination of $A$${}^{3+}$ and $M$${}^{2+}$ cations, which enables the interaction between the spatially spread $s$ orbitals of adjacent cations via shared oxygen atoms. The effect of the local atomic coordination on the band gap, the electron effective mass, the orbital composition of the conduction band, and the expected (an)isotropic character of the electron transport in layered $RAM$O${}_{4}$ is thoroughly discussed.