The S concentration dependence of lattice parameters and optical band gap of a-plane ZnOS grown epitaxially on r-plane sapphire

• High quality a-plane ZnO1−xSx films were deposited epitaxially on r-sapphire.
• ZnO1−xSx[1¯100] || sapphire [1¯1¯20] and ZnO1−xSx [0 0 0 1] || sapphire [1¯101].
• The lattice constants a and c of ZnO1−xSx increase with more S incorporation into ZnO.
• The domain matching epitaxy mode applies for a-plane ZnO1−xSx on r-plane sapphire.
• The band gap of ZnO1−xSx becomes narrower with S fraction increasing up to 43%.

High quality non-polar a-plane ZnO1−xSx films were deposited epitaxially on r-sapphire substrates by pulsed laser ablating a ZnS ceramic target in O2 atmosphere. The in-plane orientation relationship between ZnO1−xSx films and sapphire substrates was revealed by X-ray diffraction φ-scans as ZnO1−xSx  [1¯100] || sapphire [1¯1¯20] and ZnO1−xSx [0 0 0 1] || sapphire [1¯101]. Both lattice constants a and c expand with increasing S content in the ZnO1−xSx alloys. Large lattice misfit along either ZnO1−xSx [0 0 0 1] or ZnO1−xSx  [1¯100] indicated a domain matching rather than lattice matching epitaxy mode for a-plane ZnO1−xSx on r-plane sapphire. Optical measurements show high transparency of the films in visible range. The band gap of ZnO1−xSx becomes narrower with S fraction increasing up to 43%, which behaves similar to the band gap of c-plane ZnO1−xSx films grown on c-plane sapphire.