Effect of Annealing Temperature on the Structural and Optical Properties of Un-doped Bulk ZnO

In this paper, we have demonstrated the effect of annealing temperature on the structural and optical properties of ZnO. The ZnO pellets were annealed at different temperatures from 500 to 1200 0C with a step of 100 0C for one hour using a programmable furnace. Different characterization such as XRD, PL, FTIR, SEM/EDX were utilized to characterized the samples. Un-annealed sample was Zn-rich but the concentration of oxygen gradually increased with increasing annealing temperature as evident by EDX. X-Ray Diffraction (XRD) confirmed the hexagonal structure of ZnO and showed that growth was along C-axis. It was observed that with annealing, FWHM decreased and crystalline size was increased up to annealing temperature 900 0C and again decreased for higher annealing temperatures. Room temperature photoluminescence spectrum consists of two peaks and related to free exciton and defect emissions. The intensity of exciton emission was strongly depends upon the annealing temperature. This result can be attributed to the improvement of crystal structure with annealing temperature up to 900 0C because the density of oxygen vacancy related defects decreased with annealing temperature.