Epitaxial growth of wafer-scale two-dimensional polytypic ZnS thin films on ZnO substrates

In this paper, we report the first successful epitaxial synthesis of flat wafer-scale two-dimensional ZnS thin films on single-crystalline ZnO substrates with high reproducibility, stability, and reliability, despite the large lattice mismatch (approximately 20%) between ZnO and ZnS. The as-grown ZnS was composed of two crystal phases: wurtzite (WZ) and zinc blende (ZB). The epitaxial orientation between the different phases was identified as: [2-1-10] ZnO_WZ//[2-1-10] ZnS_WZ//[10-1] ZnS_ZB and (0001) ZnO_WZ//(0001) ZnS_WZ//(111) ZnS_ZB. The crystal structure and the strain profile at the interfaces were studied in detail. After a simple etching treatment, exfoliated large-area free-standing ZnS thin films were achieved for the first time. The present product is expected to become valuable to the strategy of growing large-area thin films or heterostructures with a large lattice mismatch.