Structural and optical properties of wurtzite Mg[sub x]Zn[sub 1-x]S(≤x≤0.25) films grown on (0001) Al₂O₃ by pulsed-laser deposition

Abstract

Wurtzite Mg[sub x]Zn[sub 1-x]S(≤x≤0.25) thin films have been epitaxially grown on (0001) Al₂O₃ using pulsed-laser deposition. High-quality films can be prepared at a growth temperature of 450–550 °C with (0001) ω-rocking curve full width at half maximum as narrow as 0.09°. High-resolution cross-sectional transmission electron microscopy of the films deposited at 500 °C shows the presence of the mixture of zinc-blende and wurtzite phases at the interface, and therefore the interfacial region is highly defective. However, above the critical thickness of ∼5 nm, the film bulk consists of pure wurtzite material with a very high level of crystallinity. The band edge of Mg[sub x]Zn[sub 1-x]S films examined by transmission spectroscopy at room temperature increases from 3.75 eV at x = 0 to 3.95 at x = 0.25.