Simulation And Experimental Study Of Film Epitaxial Growth In Ultraviolet Light-Emitting Diode

Deep-ultraviolet light-emitting diodes（LEDs）have been extensively studied due to their wide application in many fields such as sterilization,water purification,and medical treatment.Among them,deep ultraviolet LED thin film growth is the source process and key technology in research of deep ultraviolet LED.The current research on the growth of deep-ultraviolet LED thin films mainly relies on experiments,and the existing reports ignore or avoid the process repeatability problems in the growth of deep-ultraviolet LED thin films;in addition,the microscopic mechanism of the thin film growth process is difficult to obtain through experiments,which hinders the in-depth study of deep-ultraviolet LED film growth.In response to these problems,this article takes the growth order of each film layer when growing deep ultra violet LED films on sapphire substrates,focusing on the understanding of the growth mechanism of AlN on sapphire,the study of AlN process repeatability,the growth of AlN and AlGaN films,and the full structure of epitaxial wafers.The main research contents are as follows:1)Adsorption study of AlN on sapphire substrate:In order to study the physical and chemical process of adsorption and bonding of AlN on sapphire substrate,the first principle method was applied to study the adsorption of Alatom,N atom and AlN molecule on sapphire substrate.The adsorption energy of each adsorbed particle on the sapphire substrate surface,the final bonding state and the amount of charge transfer during the adsorption process were analysed.Meanwhile,the bonding type and difficulty degree of each particle adsorption on the sapphire surface,as well as the lattice mismatch under different adsorption states are obtained.2)Study on the repeatability of AlN buffer layer growth process:Aiming at the problem of non-repetition of AlN growth process,the method of theoretical derivation,first-principle simulation calculation and experimental verification are used to study the pre-deposited substances that may exist during the growth of the AlN buffer layer that affect the process repeatability.A pre-deposited GaN process to suppress the pre-deposited products in the reaction chamber is innovatively proposed.This process can effectively improve the repeatability of the AlN film growth process and improve the quality of the AlN film crystal to a certain extent.3)Study of AlN film growth:In order to optimize the crystal quality of AlN film in mass production chemical vapor deposition of metal organics（MOCVD）,molecular dynamics combined experiments method were used to study the growth of AlN films.Finally,high-quality AlN thin film with the（002）surface and（102）surface half widths of253 arcsec and 385 arcsec and surface roughness of 0.28 nm was obtained in experiment..In addition,the growth of AlN film on the non-polar a-plane surface was also studied by molecular dynamics simulation.4)Study of AlGaN film growth:In order to study the growth of AlGaN films on AlN surfaces with different polarities,molecular dynamics simulation combined with experimental methods were used to compare the growth of AlGaN films on Al-polar AlN and N-polar AlN surfaces.We found that AlGaN films have better surface morphology and crystal quality when grown on Al-polar AlN surfaces.At the same time,molecular dynamics methods were used to study the evolution of dislocations in AlGaN films,and real-time observation and three-dimensional visualization of dislocations in AlGaN films were realized.After further optimizing the growth parameters of AlGaN film,a high-quality AlGaN film with an Alcomposition of 56%,a dislocation density of 10⁶ cm^-2,and the surface roughness of 0.53 nm was obtained on the Alpolar AlN surface.5)Full structure growth and pe rformance characterization of deep ultraviolet LED:On the basis of optimized AlN and AlGaN film,the doped n-AlGaN,multiple quantum wells and p-AlGaN films were grown subsequently.The n-AlGaN with a doping concentration of 1.88e¹⁸ cm^-3and a mobility of 62 cm²/Vs was obtained.And the p-AlGaN with a concentration of 1.5e¹⁷ cm^-3 and a mobility of 5.3 cm²/Vs was obtained.Finally,the deep ultraviolet LED full structure with an emission wavelength of 280 nm was obtained.The optical and electrical properties of deep ultraviolet LED epitaxial wafers were characterized and compared.