Research On The Methods For Improving External Quantum Efficiency Of GaN-Based Flip-chip Light-Emitting Diodes(LEDs)

LED is widely used in information display, communications and lighting with itsadvantages of energy-saving, environmental protection. So far，GaN-based compoundsis the main epitaxial materials for LED chip which has a large band gap, high thermalconductivity and electron-hole radiative recombination efficiency; The mixture of GaNwith InN and AlN of different components can change the band gap of the material cangot the light-emitting chip with blue, green, purple and other colors. There are threecommon structures, namely, Face-up, Flip-chip and Vertical structure. Flip-chipstructure is considered to be one direction of high-power chip, as its high light exitefficiency and good thermal performance compared to the traditional Fcae-up structure,as relatively simple and high yield production process compared to the vertical structure.The external quantum efficiency is one of the important measure parameters of theelectro-optical conversion efficiency of the LED chip. As LED is toward the direction ofthe high-power, it is imperative to improve the external quantum efficiency. From theperspective of both the optical and electrical, this paper focused on how to improve theexternal quantum efficiency of GaN-based Flip-chip of the LED chips, and thefollowing work was done:In the first chapter, the significance of this study was elaborated.The status quo ofthe external quantum efficiency of the LED chips at home and abroad was analyzed,and describes the main research work.In the second chapter, the factors of the refractive index and current crowding effectthat affecting external quantum efficiency was research in-depth. Above analysis ofinfluencing factors, combined with the results of previous studies, this paper presentedsone kind of Flip-chip GaN-based LED chip structure, and the characteristics of thestructure were described.In the third chapter, The Monte Carlo ray tracing method were used to reserch onthe light extraction efficiency of LED chips before and after the sapphire substratestripped, single side and double-sides patterned, with or without the buffer layer, and thesize of patterned structure have been further selected and optimized. The double-sidespatterned sapphire was produced by the micro-processing technology and the impactionof patterned structure to luminous flux was tested and studied, and compared with thesimulation results. In the fourth chapter, the current transmission model of Flip-chip GaN-based LEDchip was studied, and the quantitative conditions of the uniform current distribution wasderived using the equivalent resistance approach and was proved by simulation.In the fifth chapter, the influence of chip size, the number of electrode branches,electrode structure, the number and location of the Bump on current density distributionof active layer of chip were researched by finite element simulation software COMSOL,and related mechanism was discussed.In the sixth chapter, the studies of article were summarized, pointed out theproblems to be further addressed, and the development proposals were put forward.