Identification of defects and impurities in hydrothermally grown ZnO single crystals by ESR

Abstract For the use of hydrothermally grown crystals in optoelectronic device applications, improved crystallinity and better control of resistivity are required. Resistivity depends on structural defects and impurities. Hydrothermal synthesis allows the mass production of ZnO single crystals at low cost. However, ZnO single crystals grown by this method still have impurities and defects. The green-yellow spectral emission observed in ZnO at room temperature is believed to be caused by defects and is attributed to the presence of oxygen vacancies or zinc interstitial atoms, but the cause is still unknown. We have cut a-plane, m-plane, and c-plane substrates from hydrothermally grown ZnO bulk single crystals and identified and studied the defects and impurities by electron spin resonance (ESR), luminescence lifetime, photoluminescence (PL), X-ray diffraction (XRD) and energy-dispersive X-ray spectroscopy (EDS).