Preparation And Investigation Of Ⅲ-Nitride Violet And Near Ultraviolet LED

Theoretically, infrared to ultraviolet (UV) emitting devices can be fabricated by using III-nitride such as GaN, InGaN and AlGaN, et al. Group III nitride based violet and UV light emitting diode (LED) due to its non-toxic, not producing ozone, high switching speed, narrow spectrum and long service life, which has a broad application prospect in the sanitation and disinfection, UV curing, lithography, security detection, medical diagnosis and water purification and other fields. At present the GaN base visible light LED technology has reached a very mature stage. However, there are still some bottlenecks such as current crowding, poor heat dissipation, ultraviolet light absorbed by the substrate and epitaxial materials, low light extraction efficiency, et al. for violet and ultraviolet LED, and limited the external quantum efficiency of violet LED and UV LED.Aiming at the problem of current crowding and poor heat dissipation of violet and UV LED. Violet LED with different electron blocking layer (EBL) were designed. The properties of violet LED with different designed EBL was simulated by APSYS software and prepared by MOCVD method respectively. Both of the results showed that violet LED with10pairs of p-AlGaN/GaN superlattice was with less current crowding, more uniform current distribution, and luminous efficiency is improved obviously, compare to the violet LED with p-AlGaN single layer.Innovatively proposed the surface micro processing technology for preparation of p-type GaN micro rod. By controlling the epitaxial growth pattern, micro rod shape p-type GaN structure was prepared, which can make more ultraviolet light escape out of the LED chip, reduce UV light absorbed by the epitaxial material, make stress in the UV LED quantum well relaxed. By using this technology the light output power of the UV LED was effectively improved, which is about88%higher than UV LED with flat surface. In order to improve the light extraction efficiency of UV LED, the influence of the nano-imprint lithography (NIL) pattern sapphire substrate (PSS) to ultraviolet LED luminous efficiency were studied previously. The experimental results show that the probability of internal reflection for UV LED made by NIL PSS was lower than that of UV LED made by other PSSs, which make the output power of UV LED made with NIL PSS higher than others.Innovatively proposed the In situ two steps growth method. The AlGaN/GaN DBR grown on sapphire substrate cracked after stress release, by controlling growth mode and overcoming the difficult growth problems of the GaN LED structure caused by the DBR crack, regrew a smooth GaN LED structure on the cracked AlGaN/GaN DBR, and effectively improved the luminous efficiency of the UV LED. Innovatively proposed the technology of directly growing UV LED with DBR on SiC substrate. By using MOCVD method and introducing the AlN/AlGaN double buffer layer to release stress, prepared Al0.2Ga0.8N/GaN DBR structure without cracks on6h-SiC(0001) substrate, then prepared high quality UV LED structures continually. The UV LED with stress released buffer and DBR on SiC substrate has the advantages, not only the SiC substrate and GaN are with lattice matching, but also the SiC substrate is with high heat conductivity, and avoid UV light absorbed by SiC substrate, is expected to be applied in the ultraviolet LED.