| Flexible devices have attracted extensive interest from researchers because of their many advantages and wide applications.The research and development of flexible devices has become an international frontier.Using GaN as p-n junction material,low cost and large area of ultra-thin glass as flexible substrate,and developing low temperature growth technology will contribute to the development of flexible inorganic light-emitting displays with large screen.Since the glass is amorphous,when a GaN thin film is grown on a glass substrate,there will be a poor quality of the crystal,a surface roughness,a polycrystalline structure.Considering that ZnO and GaN have the same hexagonal wurtzite crystal structure and a small lattice mismatch(<2%),ZnO will be great as a buffer layer when GaN thin films grow on amorphous glass.The low softening temperature of the glass poses a challenge to the growth technology and requires the development of a low temperature growth technique.Pulsed laser deposition can provide pulsed supply for target,that can increase the surface mobility of the thin film precursor on the substrate,thereby lowering the growth temperature.In this dissertation,ultra-thin glass is used as a substrate,ZnO is used as a buffer layer,and pulsed laser deposition is used to explore the low-temperature growth technology of GaN thin films.The main research results are as follows:1.A pulsed laser deposition method was used to prepare ZnO buffer layer with high c-axis growth orientation on an ultra-thin glass substrate.The effects of laser energy,substrate temperature,laser frequency,and oxygen pressure on the micro-structure,surface morphology,internal defects,optical properties,and electrical properties of ZnO thin films were investigated by the control variable method.Exploring the physical mechanism by establishing the correspondence between structures and physical properties.The results show that by optimizing the growth conditions,the obtained ZnO thin film has a hexagonal wurtzite structure,which is highly oriented along the c-axis.The film surface is smooth,even and dense,and the crystal quality is good.There are fewer internal oxygen vacancies and carriers.The concentration is 2 orders of magnitude higher than that of the ZnO bulk,and the average transmittance in the300~1200 nm band can reach 90% or more.2.On the basis of high quality ZnO buffer layer,GaN thin films were further grown at low temperature.Firstly,the samples of GaN were compared with ZnO buffer layer and ZnON layer.It was analyzed from four aspects of appearance color,diffraction peak position,section stratification and chemical composition.Finally,the GaN film formed on the ZnO buffer layer/glass substrate was determined.Subsequently,the effects of annealing treatment of different nitrogen pressure,the auxiliary growth of the ion activation source and the different nitrogen pressure growth on the crystal structure and surface morphology of GaN films were studied.The results show that when the annealing nitrogen pressure is 30 Pa,the crystalline quality of the film is better,the internal stress is minimum,and the film surface is uniform and dense.By comparing the two methods of ion activation assisted sputtering and traditional nitrogen atmosphere assisted sputtering,it was found that the GaN films prepared by traditional nitrogen atmosphere assisted method are closer to the stoichiometric ratio.For the GaN films grown under different nitrogen pressures(10~30 Pa N2),the sample grown under 20 Pa nitrogen pressure have larger grain size,smaller internal stress,and N/Ga ratio closest to the stoichiometric ratio,and GaN and ZnO are obviously stratified without apparent atomic diffusion.The research work in this dissertation can provide experimental reference for further preparation of GaN-based p-n junctions on ultra-thin glass substrates,thus providing scientific basis and technical support for the development and low-cost production of large-area inorganic light-emitting display devices on flexible amorphous substrates. |
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