J.H. Gu

Preparation, structure and optical properties of transparent conducting gallium-doped zinc oxide thin films

Abstract Highly conductive gallium-doped zinc oxide (GZO) transparent thin films were deposited on glass substrates by RF magnetron sputtering. The deposited films were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), four-point probe and UV-Vis spectrophotometer, respectively. The effect of growth temperature on the structure and optoelectrical properties of the films was investigated. The results demonstrate that high quality GZO films oriented with their crystallographic c-axis perpendicular to the substrates are obtained. The structure and optoelectrical properties of the films are highly dependent on the growth temperature. It is found that with increasing growth temperature, the average visible transmittance of the deposited films is enhanced and the residual stress in the thin films is obviously relaxed. The GZO films deposited at the growth temperature of 400°C, which have the largest grain size (74.3 nm), the lowest electrical resistivity (1.31×10-3 Ω·cm) and the maximum figure of merit (1.46×1O-2Ω-1), exhibit the best optoelectrical properties. Furthermore, the optical properties of the deposited films were determined by the optical characterization methods and the optical energy-gaps were evaluated by extrapolation method. A blue shift of the optical energy gap is observed with an increase in the growth temperature.

Effect of Argon Gas Pressure on Optical Properties of Zinc Oxide Thin Films Deposited by RF Magnetron Sputtering Technique

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.

Investigation of Optical Properties of Aluminium Doped Zinc Oxide Thin Films Deposited by Magnetron Sputtering

Aluminium doped zinc oxide (AZO) thin films were prepared by magnetron-sputtering. The optical and structural properties of the films were investigated by optical transmission spectra and X-ray diffraction (XRD) measurements, respectively. The results indicate that the AZO films have hexagonal wurtzite structure with highly c-axis preferred orientation. The optical and structural properties of the films are observed to be subjected to the argon pressure. The AZO film prepared at the argon pressure of 0.5 Pa exhibits the largest crystallite size and the highest average visible transmittance. Also, the refractive index and optical energy-gap of the films were determined by optical characterization methods. The dispersion behavior of the refractive index was studied using the Sellmeier’s dispersion model.

Influence of Substrate Temperature on the Characteristics of Zinc Oxide Thin Films Deposited by Magnetron Sputtering

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.

Study on the Optical and Electrical Properties of Organic Semiconductor Thin Films for OLEDs

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.

Properties of Indium Tin Oxide Films Prepared by RF Magnetron Sputtering at Different Substrate Temperatures

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.