Synthesis, structural and optical properties of ZnS/ZnO heterostructure-alloy hexagonal micropyramids

Abstract

Heterostructure alloys with controlled structure and composition are essential for future electronics and optoelectronics. While heterostructure formation creates sharp electronic junction, alloying allows bandgap tunability. Herein, ZnS/ZnO heterostructure-alloy hexagonal micropyramids are grown on Si/SiO2 wafers for the first time by facile thermal evaporation of ZnS powder. It is found that the pyramids with a based size of few micrometers are grown along different crystallographic directions and neighbored by ZnS microrods. XRD and XPS spectra showed that ZnS, ZnO, and ZnSO wurtzite phases coexist in the as-received samples. FESEM images, in situ point, and EDS elemental mapping spectra reveal that the micropyramids are composed of Zn, S, O, but each element's ratio changes with substrate temperature and is different at different faces of a single micropyramid. Using a high-spatial CL-FESEM, the profile of CL spectra along the substrate and at different faces in a single micropyramid were in-situ measured and disclosed red-shifted of ZnS band-edge emission with increasing substrate temperature, and the formation of new emission bands in the range from ∼345 to 352 nm. This new emission band is attributed to the formation of the ZnSO alloy phase. Our results demonstrated that the optical properties of the obtained ZnS/ZnO heterostructure-alloy hexagonal micropyramids could be tunned by controlling the substrate temperature and indicates potential applications of the ZnS/ZnO heterostructure alloy in optoelectronic and photonic applications