Papers by Author: C.Y. Yang

Abstract: Transparent conducting gallium doped zinc oxide (GaZnO) films were prepared by magnetron sputtering technique. The influence of growth temperature on the microstructural and optical properties of the films were investigated by means of X-ray diffraction (XRD), spectrophotometer and optical characterization method, respectively. The results show that all the samples are polycrystalline in nature having a hexagonal wurtzite type crystal structure with a preferred grain orientation in the (002) direction. The growth temperature significantly affects the crystal structure and optical properties of the samples. The film deposited at the growth temperature of 670 K possesses the largest grain grain, the minimum dislocation density and the lowest microstrain. The average visible transmittance and optical energy gap of the samples increase gradually with the increment of growth temperature.

Abstract: Zinc oxide (ZnO) thin films were deposited by radio frequency (RF) magnetron sputtering technique on glass substrates in pure argon gas. The optical transmission stectra of the films were measured by ultraviolet-visible spectrophotometer. The effects of argon gas pressure on optical properties of the deposited films were investigated. The optical band-gap of the films was evaluated in terms of the Taucs law. The results show that the argon gas pressure has slightly affected the optical band-gap of the deposited films. Furthermore, the refractive index and extinction coefficient of the films were determined by means of the optical characterization methods. Meanwhile, the dispersion behavior of the refractive index was studied by the single-oscillator model of Wemple and DiDomenico, and the physical parameters of the average oscillator strength, average oscillator wavelength, oscillator energy, the refractive index dispersion parameter and the dispersion energy were obtained.

Abstract: Titanium and gallium co-doped zinc oxide (TGZO) thin films with highly (002)-preferred orientation were grown on glass substrates by magnetron sputtering. The effect of thickness on structure and optical properties of the deposited films were investigated by X-ray diffractometer and spectrophotometer. The results show that the polycrystalline TGZO films consist of the hexagonal crystal structures with c-axis as the preferred growth orientation normal to the substrate, and that the thickness significantly affects the crystal structure and optical properties of the thin films. It is observed that the average transmitance in the wavelength range of the visible spectrum decreases with the increase of thickness. The TGZO thin film with about 900 nm thickness exhibits the maximum grain size, the lowest dislocation density and the minimum micro strain.

Abstract: Transparent conducting gallium-titanium codoped zinc oxide thin films were grown onto glass substrates with magnetron sputtering technique in ambient argon gas, and the influence of argon pressure on optical properties of the films were investigated. The refractive indexes of the films were calculated. It is found that the refractive index tends to increase with increasing the photon energy. Meanwhile, the dispersion behavior of the refractive index was analyzed in terms of the single-oscillator model and the oscillator parameters were obtained. Furthermore, the optical energy gaps were evaluated by single-oscillator model and Tauc’s relation, respectively. The values of optical energy gap estimated from single-oscillator model are in agreement with those determined from Tauc’s relation.

Abstract: Indium tin oxide (ITO) thin films were deposited by RF magnetron sputtering on glass substrates employing a sintered ceramic target. The influence of substrate temperature on the structural, compositional, optical and electrical properties of the thin films were investigated by X-ray diffractometer (XRD), X-ray photoelectron spectroscopy (XPS), spectrophotometer and four-point probes. All the ITO thin films show a polycrystalline indium oxide structure and have a preferred orientation along the (222) direction. The substrate temperature significantly affects the crystal structure and optoelectrical properties of the thin films. With the increment of substrate temperature, the electrical resistivity of the deposited films decreases, the crystallite dimension, optical bandgap and average transmittance in the visible region increase. The ITO thin film deposited at substrate temperature of 200 °C possesses the best synthetic optoelectrical properties, with the highest transmittance, the lowest resistivity and the highest figure of merit.

Abstract: Al-doped ZnO (ZnO:Al) thin films were deposited on glass substrates by rf magnetron sputtering technique. The effect of discharge power on the structural, optical and electrical characteristics of ZnO:Al films was investigated by X-ray diffraction (XRD), four-probe meter and optical transmission spectroscopy. The results show that the films are polycrystalline with a hexagonal wurtzite structure and preferentially oriented in the (002) crystallographic direction. The highest figure of merit of 5.58×10-3 -1 is obtained from the film prepared at the discharge power of 200 W. The average optical transmittance in the visible range of the films is over 78.2%.

Abstract: Zinc oxide (ZnO) thin films were deposited by RF magnetron sputtering on glass substrates employing a sintered ceramic target and pure argon gas. The influence of substrate temperature on microstructure and optical characteristics of the deposited films were investigated by X-ray diffractometer (XRD) and spectrophotometer. The results demonstrate that all the ZnO films have preferred orientation along (002) direction. The substrate temperature significantly affects the crystalline quality and optical characteristics of the ZnO thin films. With the increase of substrate temperature, the mean grain size, lattice spacing and optical bandgap of the films increase, the dislocation density and micro strain decrease, and the average transmitance in the wavelength range of the visible spectrum also increases.

Abstract: Organic semiconductor thin films of aluminum (III) bis(2-methyl-8-quninolinato)-4- phenylphenolate (BAlq), -naphthylphenylbiphenyl amine (NPB), and tris(8-hydroxy-quinoline) aluminum (AlQ) for organic light-emitting diodes (OLEDs) were deposited by the vacuum sublimation technique. The optical properties in the UV-visible region of the thin films were investigated by optical transmittance and absorption spectra. The band gaps were obtained from direct allowed transitions at room temperature by means of the Tauc plots. The Urbach energy and the slope of Urbach edge were evaluated, respectively according to the Urbach-edges method. The thin film devices of sandwich structure were fabricated using these organic semiconductor materials, in addition, the effective carrier mobility, free carrier density, and electrical conductivity of the thin films were calculated in terms of the measured current-voltage characteristics of the devices.

Abstract: Transparent conductive ZnGa₂O₄ thin films were prepared by magnetron sputtering. The chemical state of O, Zn and Ga in the deposited films was investigated by X-ray photoelectron spectroscopy (XPS), and the optical properties were characterized by optical transmittance spectra. The XPS studies reveal that no metallic Zn and Ga were detected in the ZnGa₂O₄ thin films, and Zn and Ga exist only in oxidized state. The optical bandgap was calculated by Tauc's theory and the optical constants were determined using Swanepoel's method. Furthermore, the dispersion behavior of the refractive index was studied by means of single-oscillator model, and the physical parameters and the refractive index dispersion parameter were obtained. The results provide some useful references for the potential application of the ZnGa₂O₄ thin films in optoelectronic devices.