First-principle calculations of structural and optoelectronic properties of wurtzite Zn1-x-yBexMgyO quaternary alloys closely lattice matched to the ZnO substrate for UV-A optoelectronic applications

Abstract

Structural and optoelectronic properties of some wurtzite Zn1-x-yBexMgyO quaternary alloys closely lattice-matched to w-ZnO substrate are investigated with density functional theory. The Zn0·75Be0·0625Mg0·1875O, Zn0·6875Be0·0625Mg0·25O and Zn0·625Be0·0625Mg0·3125O alloys having Be/Mg composition ratio in the experimentally prescribed range 2.0–4.0 are considered to achieve high quality stable wurtzite quaternary crystals. Lattice constants (a0, c0) decrease, while direct band-gap (Γ-Γ) increases with increasing Be and Mg composition sum. These optically anisotropic quaternary alloys exhibit diverse optical properties due to electronic transitions from valence O-2p to Be-2p, Be-3s, Zn-5s, Mg-4s, Mg-3p states of conduction band. Calculated optical energy gap, slightly higher than band-gap, shows blue shift with increasing Be and Mg composition sum. Calculated static optical constants ε1(0), n(0), R(0) of these alloys reduce with increasing band-gap and vice versa. These quaternary alloys with band-gaps, fundamental absorption edges and optical energy gaps in the UV-A region would have potential applications in fabricating UV-A optoelectronic devices.