The Structure Probe Of Sapphire/Graphene System And Application In ?-Nitride Growth

Light-emitting diodes based on III-nitride materials show many advantages such as small size,low energy consumption,durability,high efficiency and environmental friendly.At present,heterogeneous epitaxy is generally used in the industry to grow these III-nitride materials.There is a large lattice mismatch between the substrate and the epitaxial material resulting in a large stress and dislocation density in the obtained nitride film,and these issues lead to a decline in the quality of the core luminescent area,which ultimately lead to poor performance of LED devices.After the appearance of two-dimensional atomic crystals,two-dimensional materials led by graphene have shown great application prospects in various fields such as optics and electricity.The graphene layers are combined with each other by van der Waals force,which provides a new idea for solving the lattice mismatch between the substrate and the epitaxial layer.Thanks to the development of electron microscopy,the resolution limit of human beings has expanded to the atomic level,which facilitates the understanding of the physicochemical properties of related materials from the most basic atomic level.Due to the difficulty to grow nitride materials,this thesis introduces graphene buffer layer to improve the lattice and thermal mismatch between the substrate and the epitaxial layer.Firstly,the interface structure of graphene/sapphire is identified to be C-O-Al with advanced electron microscopy analysis method.The influence of graphene on the surface relaxation of sapphire substrate is also discussed deeply,which lays a foundation for the growth of III-nitride materials based on graphene/sapphire system.Secondly,we carefully investigate the role of graphene in nucleation of GaN and AlN.Besides,we discusses the role of graphene in reducing the dislocation density of epitaxial layer and releasing interface stress.It is found that the presence of graphene greatly reduces the biaxial stress and dislocation density of the epitaxial material.For GaN,the stress drops to be⁰.16 GPa,and the average dislocation density becomes¹0⁷ cm^-2.The blue-LED output power based on this structure is⁹0 mW at an injection current of 350 mA,which is increased by²0%compared with the conventionally prepared LED.For AlN,the stress is reduced to be0.11 GPa and the average dislocation density is as low as¹0⁸ cm^-2.Based on this construction,the UV-LED has an output power of 1.7 mW at an injection current of 80mA.Lastly,the one-step high-temperature growth method used in this thesis effectively shortens the growth time of nitride materials.This thesis proposes a general method for nitride epitaxial growth,which lays a foundation for the application of graphene in LED devices.Besides,this thesis provides a precious reference for the current industrial production of LEDs.