The electrical, electronic and optical properties of plasma surface treatment Indium Tin Oxide (ITO) thin films on glass substrates were investigated using reflection electron energy loss spectroscopy (REELS), ultraviolet photoelectron spectroscopy (UPS), X-ray photoelectron spectroscopy (XPS) and a...
The electrical, electronic and optical properties of plasma surface treatment Indium Tin Oxide (ITO) thin films on glass substrates were investigated using reflection electron energy loss spectroscopy (REELS), ultraviolet photoelectron spectroscopy (UPS), X-ray photoelectron spectroscopy (XPS) and angle-resolved XPS (AR-XPS). ITO thin films on a glass substrate were deposited using in situ SPTS by RF magnetron sputtering under argon mixed with oxygen in various fabrication conditions such as different substrate temperatures, RF power, and gas flow rates. The 70 nm-thick ITO films grown in argon mixed with oxygen (Ar:O2=20:5) with RF magnetron sputtering exhibited an optical transparency of 85% in the visible light region, a low resistivity of 5.21×10-4Ω·cm, and a high mobility of 19.15cm2/V·s. The effect of the plasma treatment on the electrical and the optical properties of ITO thin films were investigated. After performing the measurements of the band gap, the optical transmittance, and the work function of the ITO thin films, we found that the carbon organic contaminants on the substrate were completely removed and the amount of oxygen on the surface was increased after the plasma treatment. The optical transmittance and the band gap were increased with increasing plasma treatment time. In addition, the sheet resistance was decreased and the valence band maximum was reduced by 0.41eV. However, the work function was decreased by 0.34eV. The surface plasma treatment improved the electrical and the optical properties of ITO thin films, but lowered the work function, which indicates that the ITO thin films are not good enough to be utilized as transparent conducting oxide devices. In order to examine the influence of the surface plasma treatment on the work function of ITO thin films, the samples were plasma-treated in oxygen. As a result of the plasma etching, the roughness of the film was reduced with increasing plasma treatment time. The REELS measurement with the primary electron energy of 300eV revealed that the band gap of the extreme surface of the thin film was increased by 1.03eV. At 1700eV, however, the band gap of the film remained the same. The UPS result indicated that the work function was increased by 0.82eV and the XPS spectra showed that the valence band maximum was measured to be 5.32eV after the plasma treatment. The change in the work function of the extreme surface of the film is attributed to the increase in the amount of oxygen after the plasma treatment, which did not affect the electrical conductivity and the value of the band gap. XPS and AR-XPS were used to examine if the oxygen plasma treatment caused any change in the composition ratio and the depth of the ITO thin film. The spectra showed that almost all the peaks for the carbon compounds from C-H-O were eliminated after the plasma treatment. In addition, In-O bonds and O=O bonds were increased as a result of oxygen abundant in the surface of the film. The composition ratio of In:Sn:O in the film was measured to be 41:4.3:54.7, which implies that about 10% of Sn was replaced. The thickness of the film with increasing plasma treatment time of 2, 6, and 10 minutes was 75.26, 73.31, and 71.14nm, respectively, which means the plasma treatment made the film thinner by etching the surface. Since the change in the composition ratio of the film was observed below θ=20° in the AR-XPS data, we found that the effect of the plasma treatment was limited to the film thickness of 23.59nm from the surface. This suggests that the extreme of an ITO thin film is influenced by the plasma treatment. Our results demonstrated that the electronic, optical and the structural properties of plasma-treated ITO thin films in the oxygen environment were greatly improved. The decrease in the roughness and the increase in the work function proved that the plasma treatment can enhance the surface properties of the ITO thin films. The results also showed that a variety of methods used in this study are effective tools for a quantitative analysis of oxide thin films.
The electrical, electronic and optical properties of plasma surface treatment Indium Tin Oxide (ITO) thin films on glass substrates were investigated using reflection electron energy loss spectroscopy (REELS), ultraviolet photoelectron spectroscopy (UPS), X-ray photoelectron spectroscopy (XPS) and angle-resolved XPS (AR-XPS). ITO thin films on a glass substrate were deposited using in situ SPTS by RF magnetron sputtering under argon mixed with oxygen in various fabrication conditions such as different substrate temperatures, RF power, and gas flow rates. The 70 nm-thick ITO films grown in argon mixed with oxygen (Ar:O2=20:5) with RF magnetron sputtering exhibited an optical transparency of 85% in the visible light region, a low resistivity of 5.21×10-4Ω·cm, and a high mobility of 19.15cm2/V·s. The effect of the plasma treatment on the electrical and the optical properties of ITO thin films were investigated. After performing the measurements of the band gap, the optical transmittance, and the work function of the ITO thin films, we found that the carbon organic contaminants on the substrate were completely removed and the amount of oxygen on the surface was increased after the plasma treatment. The optical transmittance and the band gap were increased with increasing plasma treatment time. In addition, the sheet resistance was decreased and the valence band maximum was reduced by 0.41eV. However, the work function was decreased by 0.34eV. The surface plasma treatment improved the electrical and the optical properties of ITO thin films, but lowered the work function, which indicates that the ITO thin films are not good enough to be utilized as transparent conducting oxide devices. In order to examine the influence of the surface plasma treatment on the work function of ITO thin films, the samples were plasma-treated in oxygen. As a result of the plasma etching, the roughness of the film was reduced with increasing plasma treatment time. The REELS measurement with the primary electron energy of 300eV revealed that the band gap of the extreme surface of the thin film was increased by 1.03eV. At 1700eV, however, the band gap of the film remained the same. The UPS result indicated that the work function was increased by 0.82eV and the XPS spectra showed that the valence band maximum was measured to be 5.32eV after the plasma treatment. The change in the work function of the extreme surface of the film is attributed to the increase in the amount of oxygen after the plasma treatment, which did not affect the electrical conductivity and the value of the band gap. XPS and AR-XPS were used to examine if the oxygen plasma treatment caused any change in the composition ratio and the depth of the ITO thin film. The spectra showed that almost all the peaks for the carbon compounds from C-H-O were eliminated after the plasma treatment. In addition, In-O bonds and O=O bonds were increased as a result of oxygen abundant in the surface of the film. The composition ratio of In:Sn:O in the film was measured to be 41:4.3:54.7, which implies that about 10% of Sn was replaced. The thickness of the film with increasing plasma treatment time of 2, 6, and 10 minutes was 75.26, 73.31, and 71.14nm, respectively, which means the plasma treatment made the film thinner by etching the surface. Since the change in the composition ratio of the film was observed below θ=20° in the AR-XPS data, we found that the effect of the plasma treatment was limited to the film thickness of 23.59nm from the surface. This suggests that the extreme of an ITO thin film is influenced by the plasma treatment. Our results demonstrated that the electronic, optical and the structural properties of plasma-treated ITO thin films in the oxygen environment were greatly improved. The decrease in the roughness and the increase in the work function proved that the plasma treatment can enhance the surface properties of the ITO thin films. The results also showed that a variety of methods used in this study are effective tools for a quantitative analysis of oxide thin films.
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#ITO XPS REELS UPS Plasma Treatment
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