Low-temperature Growth Of GaN-based Thin Films On Ultrathin Glass Substrate And Preliminary Investigation Of Pn Junction

Flexible devices have become one of the international frontier topics due to their portability,shape variability,human body applicability and many other advantages.The key to the development of flexible devices lies in the selection of flexible substrate and the preparation of pn junction.In this thesis,ultrathin glass is selected as the substrate material,which is a flexible substrate material most likely to be used on a large scale.The pn junction material is Ga N with outstanding photoelectric performance.In order to achieve the growth of high-quality Ga N-based thin films on the amorphous glass substrate,Zn O is introduced as buffer layer.Zn O possesses the same crystal structure as Ga N,small lattice mismatch,and can grow along the c axis on glass.Considering the low softening temperature of glass,pulse laser deposition(PLD)is used to reduce the growth temperature,which supplies the target material by pulse and therefore improves the surface mobility of the film precursor on the substrate.In this work,the flexible "p-Ga N/(In GaN/Ga N)MQW/n-GaN/ZnO/ultrathin glass" pn junction structure is obtained by exploring and optimizing the low-temperature growth conditions of n-Ga N and p-Ga N thin films.The microstructure and physical properties of thin films and pn junctions were characterized by X-ray diffraction,scanning electron microscopy,atomic force microscopy,energy spectrum,X-ray photoelectron spectroscopy,fluorescence spectrophotometer and stress platform.The main results are as follows:1.The Si-doped n-GaN thin films were grown on the ultrathin glass substrate at low temperature by using the PLD method,with the high-quality Zn O thin film grown along the c axis as buffer layer.Thus the "n-Ga N/Zn O/ultrathin glass" structure was formed.The crystal structure,surface morphology,interface structure,chemical composition,ionic valence state,optical and mechanical properties of n-Ga N thin films were systematically studied by adjusting the growth conditions,including buffer-layer thickness,film growth time,substrate temperature and laser repetition frequency.Cosequently,the growth process can be optimized to improve the microstructure and physical properties of n-Ga N thin film.The results show that the low-temperature growth of n-GaN thin film can be realized on the ultrathin glass substrate by optimizing the PLD growth conditions.The film has a preferred growth orientation along the c axis,good crystallization quality,smooth,flat,uniform and dense surface,strong UV emission,good mechanical properties and high stability of optical properties under stress.2.Based on the low-temperature growth of "n-GaN/ZnO/ultrathin glass" structure,the Mg-doped p-Ga N thin film was further grown to obtain a flexible Ga N-based pn junction.Two types of junctions,p-Ga N/(Ga N/In Ga N)/n-Ga N/Zn O/ultrathin glass and p-Ga N/(Ga N/In Ga N)/n-Ga N/Zn O/ultrathin glass,were achieved by changing the growth order of In Ga N and Ga N in the MQW structure.The potimization of growth conditions was preliminarily explored by studying the crystal structure,surface morphology,ionic valence state,optical and mechanical properties of pn junctions.The results show that the pn junction with In GaN deposited first has higher crystal quality,larger grain size,denser surface,stronger UV emission,good mechanical properties and higher stability of optical properties under stress.The research work of this thesis can provide experimental reference for the preparation of Ga N-based pn junction on ultrathin glass substrate,and therefore provide scientific basis and technical support for the research and development of flexible large-area inorganic light-emitting display devices in the future.