Abstract
This study focuses on the growth and physical properties of ZnO thin films on different substrates grown by mist-CVD enhanced with ozone (O3) gas produced by corona discharge plasma using O2. Here, O3 is used to eliminate the defects related to oxygen in ZnO thin films. ZnO thin films are grown on amorphous soda-lime glass (SLG) and single crystals SiO2/Si (100) and c-plane Al2O3 substrates at 350°C of low growth temperature. All ZnO thin films show dominant (0002) diffraction peaks from X-ray diffraction (XRD). As expected, full width at half maximum (FWHM) of (0002) is decreasing in ZnO thin films on single-crystal substrates, especially c-Al2O3 due to similar crystal structure. It is found that the strain in the films is lowest in ZnO/c-Al2O3. The surface morphologies of the thin films are studied with atomic force microscopy (AFM) and scanning electron microscopy (SEM) measurements. Grown ZnO films have a hexagonal and triangular nanostructure with different nanostructure sizes depending on the used substrate types. The calculated surface roughness is dramatically decreased in ZnO/c-Al2O3 compared to the other grown structures. The confocal Raman measurements show the E2(H) peak of ZnO thin films at 437 cm−1. It is suggested that O3 gas produced by corona discharge plasma using O2 can be useful to obtain better crystal quality and physical properties in ZnO thin films.
Highlights
Zinc oxide (ZnO), which is one of the most studied transparent conductive oxide (TCO), is a wide bandgap semiconductor material with a 3.37 eV bandgap value and a large exciton binding energy of 60 meV [1, 2]
In this study, ZnO thin films are on different substrates soda-lime glass (SLG), SiO2/p-Si(100), and c-Al2O3 by mist-CVD with O3-rich O2 gas where O3 gas is generated by a corona discharge generator. e structural and optical properties of the grown thin films are studied by X-ray diffraction (XRD), atomic force microscope (AFM), scanning electron microscope (SEM)\, and confocal Raman spectroscopy measurements
According to XRD results, ZnO thin films are preferentially grown in a wurtzite hexagonal crystal system without any other crystal phases. ree well-defined ZnO peaks have been seen, displayed as the (1010), (0002), and (10-11) peaks showing the ZnO polycrystalline wurtzite structure
Summary
Zinc oxide (ZnO), which is one of the most studied transparent conductive oxide (TCO), is a wide bandgap semiconductor material with a 3.37 eV bandgap value and a large exciton binding energy of 60 meV [1, 2]. The usage of oxygen (O2), argon (Ar), and nitrogen (N2) as a carrier gas was reported in some studies [24,25,26] In addition to these carrier gases, hydrogen peroxide (H2O2) can be used as an oxidant in ZnO growths [27]. Ese defects can give rise to the poor physical properties at ZnO, especially in both electronic and optical properties Among these defects, the Vo defect is unintentionally formed in the crystal without doping and has a luminescence of about 500 nm that is called green luminescence. The Vo defect is unintentionally formed in the crystal without doping and has a luminescence of about 500 nm that is called green luminescence To minimize these defects in the lattice system, especially Vo, O3 is used as an oxygen source in the MBE system, and more oriented ZnO films can be obtained [29]. In this study, ZnO thin films are on different substrates SLG, SiO2/p-Si(100), and c-Al2O3 by mist-CVD with O3-rich O2 gas where O3 gas is generated by a corona discharge generator. e structural and optical properties of the grown thin films are studied by X-ray diffraction (XRD), atomic force microscope (AFM), scanning electron microscope (SEM)\, and confocal Raman spectroscopy measurements
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