Study On MOCVD Growth Method Of AlN And High Al Component AlGaN Materials

Nitride is the most attractive material in the third generation of semiconductor materials.The advancement and development of GaN-based blue LED technology has revolutionized the lighting industry.Compared with blue LEDs,deep-UV LEDs have a wider range of applications,and in addition to traditional lighting,they can be widely used in sterilization,UV curing,secure communications,agriculture and medical fields.Because of the small size,high energy efficiency,durability,environmental protection,low voltage and long life,the UV solid-state light source has replaced the traditional mercury lamp,which is driven by the application of solid-state lighting and disinfection.Subdivided areas will become tens of billions of markets.Compared with blue LEDs,deep ultraviolet LED devices still have a lot of technical problems that need to be overcome.The main technical bottlenecks include: First,the AlN and AlGaN materials required for deep ultraviolet LEDs have larger crystals than GaN materials.Lattice mismatch and thermal mismatch,a large number of defects caused by these mismatches will restrict the realization of the device;secondly,the activation of p-doped Mg increases with the increase of Al composition,low hole concentration and low mobility It seriously affects the photoelectric characteristics of the device;in addition,the optical resistance of the contact resistance and the contact layer,and the high surface resistance of p-AlGaN also affect device efficiency.In this paper,the problems of lattice mismatch and thermal mismatch between AlN materials and substrates and the difficulty in preparation of high quality AlGaN materials are studied.The metal organic compound chemical vapor deposition(MOCVD)method is used to study the AlN pulse method and pulse addition.Epitaxial growth of materials is performed by a continuous method,a method of inserting an annealing layer,and an epitaxial method such as mobility enhancement epitaxy(MEE).The epitaxial materials were characterized by high-resolution X-ray diffraction(XRD),atomic force microscopy(AFM),Raman tester and other characterization methods.In order to reduce the dislocation density in the AlN substrate,the epitaxial growth of the material was carried out by pulse method and pulse plus continuous method.The number of pulses,the thickness of the film and the flow rate of ammonia during the growth process were found to effectively reduce the film.The dislocation density and surface topography are also improved,and the surface roughness of the AlN substrate is also reduced.It laid the foundation for the subsequent growth of the AlGaN layer.Subsequently,the AlN layer was epitaxially grown by insert annealing layer and mobility enhancement method,and the dislocation density and surface morphology in the film were also improved.The AlGaN substrate was characterized by a low dislocation density and a flat surface of the AlN substrate.It was found that the surface morphology of the AlGaN material on the better quality AlN substrate grown by changing the process was better.Compared with blue LEDs,deep ultraviolet LED devices still have a lot of technical problems that need to be overcome.The main technical bottlenecks include: First,the AlN and AlGaN materials required for deep ultraviolet LEDs have larger crystals than GaN materials.Lattice mismatch and thermal mismatch,a large number of defects caused by these mismatches will restrict the realization of the device;secondly,the activation of p-doped Mg increases with the increase of Al composition,low hole concentration and low mobility It seriously affects the photoelectric characteristics of the device;in addition,the optical resistance of the contact resistance and the contact layer,and the high surface resistance of p-AlGaN also affect device efficiency.In view of the technical bottleneck faced by the above-mentioned deep ultraviolet LED devices,further research is needed from the aspects of material quality,doping,quantum efficiency,and light extraction efficiency.The main contents that can be studied include: high performance n-type and p-type AlGaN doping studies..For P-type ? doping,superlattice structure doping,composition gradient polarization doping and other doping techniques;high quantum efficiency epitaxial structure design and growth technology;efficient light extraction technology.