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Crystallization kinetics evaluated by the modified formula and optical properties of CdO and ZnO in 0.5ZnO-0.5CdO thin films

Bo Huang,Hsueh-Liang Chu,Moo-Chin Wang,Cheng-Li Wang,Weng-Sing Hwang,Chao Liu,Horng-Huey Ko,Xiujian Zhao

Crystallization kinetics evaluated by the modified formula and optical properties of CdO and ZnO in 0.5ZnO-0.5CdO thin films have been investigated. The characterization used grazing incidence X-ray diffraction (GIXRD), transmission electron microscopy (TEM), selected area electron diffraction (SAED), high-resolution TEM (HRTEM) and ultraviolet–visible (UV–Vis) spectrophotometry. When the thin films are annealed at temperatures from 573 K to 773 K for 10–60 min, the GIXRD results show that all the films are composed of CdO and ZnO as major and second phases, respectively. In addition, a trace phase of CdSiO 3 appeared for thin films annealed at 723 K and 773 K for 45 and 60 min, respectively, while CdSiO 3 also appeared when annealing at 773 K for 30 min. The crystallinity of CdO increases with annealing temperature and duration, whereas the crystallinity of ZnO increases only slightly with temperature and duration. The activation energies of ZnO and CdO crystallization in 0.5ZnO-0.5CdO thin films are 49.51 kJ/mol and 112.45 kJ/mol, respectively. The crystallization of CdO and ZnO can be described by a modified formula: ln ( 1 1 − α ′ ) = [ 30 t × exp ( − 49.51 × 10 3 R T ) ] 0.24 and ln ( 1 1 − α ′ ) = [ 104820 t × exp ( − 112.45 × 10 3 R T ) ] 0.27 , for 573 K ≤  T  ≤ 773 K and 10 min ≤  t  ≤ 60 min, respectively. All films have an average optical transparency of nearly 80% in the wavelength range greater than 500 nm in the visible range, and the band gap energy of the thin films increases from 2.68 eV to 3.10 eV as the crystallinity of ZnO increases from 5.12% to 20.91% when the thin films are annealed for 60 min at 573 K–773 K and shows a blueshift effect.