High dielectric constant and wide band gap inverse silver oxide phases of the ordered ternary alloys of SiO2, GeO2, and SnO2

Abstract

High dielectric constant and wide band gap oxides have important technological applications. The crystalline oxide polymorphs having lattice constant compatibility to silicon are particularly desirable. One recently reported candidate is the inverse silver oxide phase of SiO2. A first-principles study of this system together with its isovalent equivalents GeO2 and SnO2 as well as their ternary alloys is performed. Within the framework of density functional theory both the generalized gradient approximation and local density approximation (LDA) are employed to obtain their structural properties, elastic constants, and electronic band structures. To check the stability of these materials, phonon dispersion curves are computed which indicate that GeO2 and SnO2 have negative phonon branches whereas their ternary alloys Si0.5 Ge0.5 O2, Si0.5 Sn0.5 O2, and Ge0.5 Sn0.5 O2 are all stable within the LDA possessing dielectric constants ranging between 10 and 20. Furthermore, the lattice constant of Si0.5 Ge0.5 O2 is virtually identical to the Si(100) surface. The GW band gaps of the stable materials are computed which restore the wide band gap values in addition to their high dielectric constants.