Preparation And Characteristics Of ZnO-Based Thin Films And Devices

ZnO is a direct wide band-gap semiconductor(3.37 eV at room temperature). Compared to GaN, ITO and SnO₂, ZnO has many advantages, such as abundance in nature, low cost, relatively low deposition temperature and stability in hydrogen plasma. So it is a very promising semiconductor to play an important role in future.Transparent conductive oxides are important opoelectronic materials for a variety of applications in the fabrication of various devices such as electro-optical devices, thin-film solar cell, surface acoustic wave devices, flat panel liquid crystal display devices, infrared reflector and so on. Doping ZnO with B, Al, Ga, In can increase the conductivity by an order of magnitude. By now, many film growth techniques have been used to prepare transparent conductive ZnO films. Among the different techniques used for the preparation of ZnO films, DC reactive magnetron sputtering method is promising in preparing transparent conductive ZnO thin films due to the simplicity of the growth process required and high growth rate. Compared to other film growth techniques, large-area films can be prepared by this method. So it is a very promising techniques to prepare ZnO thin films.It is known that alloying ZnO with MgO enables widening of band gap of ZnO. And Zn_1-xMg_xO has been considered as a suitable material for the barrier layers in ZnO/ZnMgO superlattice structures. And it can form 2DEG structure if we can prepared ZnMgO thin films with high carrier concentration. People have been prepared Zn_1-xMg_xO thin films by several techniques, such as MOCVD, MBE and so on. But there is few reports to prepare and characterize the Zn_1-xMg_xO film by DC reactive magnetron sputtering method. The DC reactive magnetron sputtering technology has been applied to industrialization, So Zn_1-xMg_xO thin films prepared by DC reactive magnetron sputtering method is very meaningful to study.In this paper, highly transparent conductive ZnO:Ga thin films were prepared on glass substrate by DC reactive magnetron sputtering technique. The influence of Ga element, substrates, oxygen partial pressure, film's thickness and ambient in annealing on the film's properties has been studied. And we prepared ZnO-based transparent electrode and ZnO-based transparent heat-generation device. Besides, we prepared Zn_1-xMg_xO film by DC reactive magnetron sputtering method. The influence of substrate temperature and ambient in growth has been studied. The main results are obtained as follows:1. Highly transparent conductive ZnO:Ga thin films have been prepared on glass substrate by DC reactive magnetron sputtering. The lowest resistivity of the film is 3.7×10^-4Ωcm.2. The influence of oxygen partial pressure on the properties of the ZnO:Ga thin films has been studied, and the results show that the oxygen partial pressure can strongly influence the properties of the films. We can make highly conductive ZnO:Ga films only in a narrow range of oxgen partial pressure. The thinkness of the film can affect the properties of the films. The electrical properties of the ZnO:Ga thin films will be weaken, if the thickness is too small or too large. The kind of ambient in annealing will affect the electrical properties of the ZnO:Ga thin films. The results show the electrical properties of ZnO:Ga thin films will be improved when it is annealed in vacuum or Ar ambient in 450℃for 30 minutes. And the electrical properties of ZnO.Ga thin films will be weaken when it is annealed in oxygen or air-ambient in 450℃for 30 minutes.3. We prepared ZnO-based transparent electrode and ZnO-based transparent heat-generation device. The electrode has a high transmittance of 90% in the visible range, and it has a resistivity of 4.8×10^-4Ωcm. The ZnO-based transparent heat-generation film also has a high transmittance of 90% in the visible range, and the device can get a temperature of 150℃when we put a voltage of 19V(AC) on the device only in 28 s.4. We prepared Zn_1-xMg_xO films, the bandgap of which can be tuned by change the Mg content in the films by DC reactive magnetron sputtering. The influence of substrate temperature and ambient in the films'growth on the properties of the Zn_1-xMg_xO thin films have been studied. The results show that the high-quality Zn_1-xMg_xO thin film can be get only in suitable substrate temperature and ambient composition.