Study On Optoelectronic Devices Based On Zinc Oxide Semiconductor Thin Films

In the past few years, people have been interested on the transparent conductive oxide(TCO). Due to its high visible light transmittance and electrical conductivity, TCO thin films has been widely used in various electronic and optoelectronic applications, such as displays, solar cells and optoelectronic devices. ZnO is a Ⅱ-Ⅵ compound semiconductor with a wide direct band gap of 3.37 eV at room temperature. It has an exciton binding energy of 60 meV. In addition, Zn O has a remarkable optical and electrical properties with high chemical and thermal stability and high melting point. Furthermore, ZnO has high commercial value because of its rich raw materials, low cost, non-toxic and harmless to the environment, the simple preparation process and so on. Therefore, more attentions have been paid to it and it has been a hot topic. It is very suitable for the preparation of varieties of optical devices, such as light emitting diodes, lasers, field effect transistors and so on. In this work, we manufacture the Ag/ZnO Schottky diodes and IZO thin film transistors by the RF-magnetron sputtering method. Afterwards, we investigate the electrical characterization of them.In this paper, the Zn O thin films were grown by RF-magnetron sputtering on commercially available indium tin oxide(ITO) coated glass substrates. During deposition, the substrate was set to a temperature of 500℃.Then, the crystalline structure of the ZnO thin film was characterized by the X-ray diffraction(XRD) technique. The optical transmittance was recorded with a UV-VIS-NIR double beam spectrophotometer in the wavelength range of 300 to 800 nm. From the XRD pattern of ZnO thin film, we can see that ZnO has a preferred orientation of C axis and the calculated grain size is about 19.5 nm. From the transmittance spectra of the ZnO thin film, we can see that the average transmittance is very high within the visible region. The ZnO optical band gap obtained from the absorption spectrum is about 3.24 eV at room temperature. Based on this, we manufacture the Ag/ZnO Schottky diodes and analyze the influence of various illumination intensities and temperature on the electrical properties of the device. We found that the barrier height and ideality factor decrease with increasing illumination intensity. The values of Rs are decreased with increasing illumination intensity. Furthermore, we have investigated the temperature-dependent electrical characteristics of the Ag/ZnO Schottky diode in the temperature range of 298-343 K. It is found that a decrease of n and an increase in φb with increasing temperature. The RS decreases with increase in temperature from 298 to 343 K. At last, we prepared the ZnO Schottky gate transistor and analyzed its electrical properties.Finally, we use three different preparation methods to make a bottom gate type IZO thin film transistor. We conducted a vacuum annealing on the transistor. The current-voltage characteristics of the transistor were measured by using a Keithley 4200 semiconductor parameter analyzer. Then, we calculated the ratio of the saturation current and minimum current, the threshold voltage and saturation mobility.