Fabrication And Study Of Sapphire Micro-nano Patterned Substrate In Light Emitting Diodes

As the fourth-generation lighting source,light-emitting diodes(LEDs)have a series of advantages such as long life,energy saving,environmental protection and rich colors.From its invention to the present,it has been sought after by people and its light-emitting efficiency has been a hot research object for researchers.With the continuous development of LEDs,obtaining more efficient LEDs has become a researcher's demand.Currently the main reasons for the low light-emitting efficiency of LEDs are their lower internal quantum efficiency(IQE)and lower light extraction efficiency(LEE).In order to obtain higher light-emitting efficiency,researchers mainly focus on improving their IQE and LEE.The patterned sapphire substrate(PSS)technology is the most commonly used method in today's LEDs to simultaneously increase the IQE and LEE in the LED.The main research work of this paper is to focus on the PSS.In this paper,the development of planar sapphire substrates,micro-patterned sapphire substrates,micro-nano hybrid patterned sapphire substrates and nano-patterned sapphire substrates are introduced in detail,and the micro-nano hybrid patterned sapphire substrate and nano patterned sapphire substrate are studied systematically.(1)The micro-nano hybrid patterned sapphire substrate can not only improve the crystal quality of the epitaxial layer,overcome dislocations caused by lattice mismatch stress stretching,but also increase the LEE of the LED device by increasing light scattering.We propose a selective wet etching process for commercial sapphire micro patterned substrates,and successfully fabricate various micro-nano hybrid patterned sapphire substrates.Firstly,a selective-area Si O₂ mask is fabricated through unfull exposure lithography instead of conventional overlay lithography.Then,by carefully controlling the exposure time,the initial etching process can be well controlled so that only the top of the PSS is etched.As the etching time increases,the surface of the PSS will be continuously etched,and the overall morphology will be continuously evolved such that tapered,crater shaped,clover shaped and other shaped micro-nano hybrid patterned sapphire substrates are obtained.In the meantime,we also found that the selective area etching process of sapphire is closely related to the pattern of the Si O₂ mask,and the inclined angle of the patterned surface greatly affects the selective etching process.(2)In this paper,we propose a fabrication process for ultra-thin patterned sapphire substrates.The main structure of the ultra-thin patterned substrates is sapphire patterned materials with ultra-thin sidewalls.Air cavities with ultra-low refractive index can be formed when LED epitaxial layers are grown on the ultra-thin patterned substrates.Because the refractive indices of air cavities and sapphire materials are very different,ultra-thin patterned substrates can greatly improve the device's light scattering ability and LEE.We propose the technology of fabricating ultra-thin patterned sapphire substrate by Anodic alumium oxide(AAO)template method and nanospheres lithography technology.Through the comparison of experimental results,we find that the patterned sapphire substrate prepared by the AAO template method tends to have the phenomenon of defects in patterned shapes,while the technology of preparing the patterned sapphire substrate by the nanospheres lithography is not only low cost,simple in steps,but also can fabricate the ultra-thin sapphire substrate in large-area.In the end,we have successfully produced a large area of ultra-thin patterned sapphire substrate by the nanospheres lithography.