Abstract
This paper examines the growth of undoped and doped thin films with (Co and In) on glass substrate at 350°C using ultrasonic spray technique. We have investigated the influence of doping concentrations ranging from 0 to 4 wt.% on structural, optical, and electrical properties of ZnO thin films. Zinc acetate dehydrate, CoCl3 4H2O or InCl3, ethanol, and monoethanolamine were used as a starting materials, dopant source, solvent, and stabilizer, respectively. The X-ray diffraction analysis indicated that the undoped and doped ZnO thin films have polycrystalline nature and hexagonal wurtzite structure with (002) preferential orientation. The maximum average crystallite sizes of ZnO:Co and ZnO:In were 55.46 and 45.78 nm at concentrations of 2 wt.% Co and 3 wt.% In, respectively, indicating that the crystallinity of doped films improved after doping. The optical absorption spectra showed that all undoped and doped ZnO films are transparent within the visible wavelength region. The band gap energy of ZnO:Co thin films increased after doping from 3.25 to 3.36 eV; however, the optical gap of ZnO:In decreases after doping from 3.25 to 3.18 eV, indicating the increase and decrease, respectively, in the transition tail width. The electrical conductivity of doped films is stabilized after doping. Transparent, conductive Co-doped ZnO thin films deposited by ultrasonic spray technique are of good quality.
Highlights
Zinc oxide (ZnO), which is one of the most important binary II-VI semiconductor compounds, has a hexagonal wurtzite structure and a natural n-type electrical conductivity with a direct energy wide band gap of 3.37 eV at room temperature and a large exciton binding energy [1]
The CZO and IZO thin films were deposited on glass substrate by ultrasonic spray technique; at a substrate temperature of 350°C, we have studied the effect of the doping concentration on structural, optical, and electrical properties of ZnO thin films
Crystalline structure The X-ray diffraction patterns of Co-doped ZnO and Indoped ZnO thin films with doping levels are presented in Figures 1 and 2, respectively
Summary
Zinc oxide (ZnO), which is one of the most important binary II-VI semiconductor compounds, has a hexagonal wurtzite structure and a natural n-type electrical conductivity with a direct energy wide band gap of 3.37 eV at room temperature and a large exciton binding energy (approximately 60 meV) [1]. The doped ZnO thin films have various applications such as transparent conductors, in ferromagnetism, semiconductors, and in piezoelectric and solar cells; the films have low resistivity and good optical gap energy at low temperature and are transparent in the visible region. A substrate temperature of 350°C, we have studied the effect of the doping concentration on structural, optical, and electrical properties of ZnO thin films. The main goal for this research is to find the optimum doping concentration which gives highly semiconducting properties of ZnO:Co and ZnO:In thin films
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