Analysis And Preparation Of Novel Gan-based Light-Emitting Diode Chip

Recently, with the development of design and manufacture of semiconductor materials and devices, the performance of light-emitting diodes (LEDs) has been improved rapidly. Extensive attentions have been paid to LEDs in the domain of solid-state lighting. As the base of white LED lighting the high power GaN-based LED chips has been studied widely, and great efforts have been paid to obtain high-efficiency LED chips. In this thesis, optical modeling, electrical modeling, structure design optimizing and processing technology of the high power GaN-based LED chips were studied to achieve high efficiency.Optical modeling of GaN-based LED chips was studied. Optical modeling in terms of finite element method based on electromagnetics theory was developed, in which light-emitting unit, absorbing boundary, meshing and solution was discussed. Then Monte Carlo ray tracing method based on geometrical optics theory was developed, in which optical parameters of the LED chip materials such as refractive index and absorption coefficient were analyzed and summarized systematically with both experiments and calculation. By comparisons between experimental results and simulated data of light extraction efficiency of GaN-based LED chips with patterned indium tin oxide (ITO) layer, the precision and feasibility of the Monte Carlo ray tracing simulation was validated.Modeling of current spreading in LED chips was studied. Coupled three-dimensional modeling of current spreading and thermal effects was developed based on semiconductor physics and heat conduction theory, in which the fundamental equations and boundary conditions were discussed in detail. By comparisons of experimental results with simulated data of current spreading in GaN-based LED chips with two different mesa structures, the feasibility of the model for optimizing mesa structures of LED chips was validated.With the developed optical model the light extraction efficiency of LED chips with different micro-structures was analyzed and discussed adequately. Based on the analysis of current spreading and heat distribution in LED chips with different mesa structures by the electrical model forementioned, some design rules for mesa structures were obtained. A new LED chip structure with grooves was presented based on the comprehensive analysis of the light extraction and current spreading of LED chips. And improvement of light extraction and current spreading in the LED chip with grooves was discussed, which indicated that the new structure could be adopted in size ultra-scalable LED chips.Finally, some experiments about the key techniques in LED chip manufacture were performed. Effect of different metallization schemes and annealing processing on the specific contact resistivity of ohmic contact to p-type GaN was studied and it was found that the specific contact resistivity was reduced effectively under 500℃annealing condition. Then adequate experiments about dry etching of GaN epitaxial layers were carried out to obtain optimized etching processing parameters for manufacturing LED chips with grooves. The LED chips with grooves were obtained through standard manufacture procedure. It was found from the results of optical and electrical performance test that the saturation of light output power with increased injected current was much better in new LED chips with grooves than that of conventional LED chips, which indicated the advantage of the new structure in size ultra-scalable LED chips.