Preparation Of ZnO Buffer Layer Film By Rf Magnetron Sputtering Method For The Production Of High-quality GaN Substrate

LED substrate determines the LED device manufacturing line, and will seriously affect the overall performance of LED devices. Self-supporting high-quality GaN substrate is an important trend of the high power LED development in the future. However, GaN substrate crystal growth is difficult to use conventional preparation techniques; the sapphire was often used as substrate for epitaxial growth of GaN thin films. Thermal expansion coefficient difference and lattice mismatch caused by heteroepitaxial would significantly reduce the quality of GaN films. ZnO and GaN have the same lattice structure .the lattice constant and thermal expansion coefficient of ZnO and GaN is also very similar, therefore, high-quality ZnO thin films can serve as a buffer layer of GaN film growth.In this thesis, ZnO ceramic target was selected as raw material, access of oxygen and argon, according to the orthogonal experimental method by magnetron sputtering, prepare ZnO thin films on sapphire chip, and mainly study the effet of the sputtering temperature, the ratio of oxygen and argon, sputtering pressure, sputtering time and air annealing on the crystal structure, surface morphology, crystal orientation, photoluminescence properties and film thickness of ZnO thin films. By using SEM, AFM, XRD, PL spectra tester, and other instruments to measure the performance characterization of ZnO thin films.The results show that: According to orthogonal experiment, the temperature change has the most affected on the structure of ZnO thin films and crystalline and photoluminescence properties. When the sputtering temperature equal 250oC, zinc oxide film has excellent properties; annealing can improve the crystallinity and photoluminescence properties of ZnO thin films, besides, annealing can promote adhesion between film and substrate. When the annealing temperature equal 800oC, thermal insulation 1h, annealed under air atmosphere, (002) orientation of ZnO thin film is significantly enhanced, more uniform grain refinement; when the annealing temperature equal 600oC, thermal insulation 1h, annealed under air atmosphere, ZnO thin films has the better luminescent properties. Finally, the best conditions of processing high-quality ZnO buffer layer have been found: the flow rate ratio of oxygen and argon gas is 2:1, sputtering pressure is the 1Pa, thin film deposition temperature is 250oC, thin film deposition time is 2h, annealing atmosphere is the air, the annealing temperature range between 600oC to 800oC and insulation 1h. High-quality GaN substrates may be expected to use widely in area of the buffer layer.