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

摘要

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 O-2 atmosphere. The in-plane orientation relationship between ZnO1-xSx films and sapphire substrates was revealed by X-ray diffraction phi-scans as ZnO1-xSx [($) over bar 100] parallel to sapphire [(1) over bar(1) over bar 20] and ZnO1-xSx [0001] parallel to apphire [(1) over bar 101]. Both lattice constants a and c expand with increasing S content in the ZnO1-xSx alloys. Large lattice misfit along either ZnO1-xSx [0001] or ZnO1-xSx [(1) over bar 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. (C) 2015 Elsevier B.V. All rights reserved.