Multifractal, structural, and optical properties of Mn-doped ZnO films

Zn1−xMnxO (x ≈ 0.07) films were sputter deposited on Si (0 0 1) and fused SiO2 substrates and were annealed at different temperatures ranging from 600 to 800 °C. The influence of postgrowth annealing on multifractal, structural and optical properties of Zn1−xMnxO films has been investigated by atomic force microscope (AFM), high-resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), UV/vis spectrophotometry. A statistical analysis based on multifractal formalism show the nonuniformity of the height distribution increases as the annealing temperature is increased. All as grown and annealed films are textured having preferred orientation along the wurzite c axis. The HRTEM and SAED studies indicate that the Mn doped ZnO film is of high quality, uniform, and free of clustering/segregated phases. The as grown film is in a state of compressive stress and the stress can be largely relieved with annealing temperature of above 700 °C. The optical band gap was found to be 3.25 eV for undoped ZnO film and 3.12 eV for as grown Zn1−xMnxO (x ≈ 0.07) film. For annealed ZnMnO films the band gap was found to increase continuously with an increase in annealing temperature.