Comparative study of photoluminescence and morphological properties between Zn-polar and O-polar faces in ZnO single crystals

This work discussed the properties of (0001)-oriented with Zn-polar and O-polar faces of single crystal ZnO samples synthesized by the hydrothermal crystallization method. The properties, such as structure, photoluminescence and morphology, of these samples were analyzed using Raman spectroscopy X-ray diffraction (XRD), photoluminescence (PL), and scanning electron microscopy (SEM), respectively. The results of Raman spectra and XRD patterns confirmed the presence of a hexagonal crystal structure of the ZnO samples grown along the c-axis. PL measurements revealed significant differences in visible and near-band-edge emissions between the two polar faces. The intensities of two distinct PL bands were comparatively higher on the O-face than on the Zn-face, suggesting a greater concentration of point defects on the Zn-face. Finally, SEM micrographs demonstrated that the O-face is notably flatter than the Zn-face. This smoother surface implies a lower density of structural defects (e.g., vacancies or dislocations), thereby enhancing the photoluminescence intensity on the O-face. By analyzing these properties, the O-face of ZnO samples is more suitable for their use in different applications, such as light-emitting diodes, displays, solar cells, and biosensors. • Comparative study of Zn-polar (0001) and O-polar (000-1) surfaces in bulk ZnO single crystals. • The study correlates defect-related visible emission with surface quality, in addition to analyzing excitonic transitions. • The O-polar surface exhibits higher photoluminescence (PL) intensity than the Zn-polar surface, with intensity ratios indicating a greater concentration of point defects on the Zn-face. • Surface morphology analysis reveals that smoother surfaces are associated with a reduced density of structural defects.