Investigation of the effects of thermal annealing on the structural, morphological and optical properties of nanostructured Mn doped ZnO thin films

The control of the optical properties of ZnO nanostructured thin films by using different dopant elements paves the way for the development of potential materials for photonic and optoelectronic applications. In this work manganese (Mn) doped ZnO thin films were fabricated by rapid thermal evaporation method on a glass substrate having the same Mn content level of similar to 10% and annealed at different temperatures. XRD analysis showed that the annealed layers have hexagonal wurtzite structure, however, the unannealed layers showed only Zn peaks without any preferential direction. The elemental analysis of the films has been investigated by XPS, which revealed the presence of Mn and oxygen atoms for all layers. In addition, it was observed by FIB-SEM that the morphology of thin films changed with the annealing temperature. For an anneal at 500 degrees C nanoneedles appeared. Raman spectroscopy showed E-1 (TO) mode in the sample annealed at 500 degrees C which was attributed with the formation of nanoneedles structures. The optical transmission of the annealed films was in the range of 75-77% and the optical bandgap varied from 3.97 to 3.72 eV. These variations are related to the structural and morphological changes of the thin films with annealing temperature.

Automated summary

Control of optical properties of ZnO nanostructured thin films using different dopant elements was studied, unveiling the effects of annealing temperature on structural, morphological changes and optical properties. XRD, XPS, FIB-SEM, and Raman spectroscopy were employed, showing that annealing led to the formation of nanoneedles structures and variations in optical transmission and bandgap.