Study On GaN-based LED Chip With High Light Extraction Efficiency

GaN based light emitting diode was widely used in solid-state lighting and display field.The improvement of light output efficiency is extremely important for GaN based LED chips.LED chips with SiO2micro-structure array backside reflector were designed andfabricated to improve the light output power. Monte Carlo rays tracing method was used tosimulate the light output efficiency. The simulation results show that the LED chip withpatterned backside reflector has a7.5%enhancement of light output efficiency as compared tothe LED chip with flat backside reflector. The experimental results show that the light outputpower of LED chips with patterned back reflector can be increased by8.4%, while the lightoutput efficiency can be improved by7.6%in20mA and electrical properties has nodegradation.The photolithography and wet-etching were used to fabricate GaN-based LED chips withsurface-textured ITO layer. After the triangle-lattice of close-packed micro-holes wereprepared, the light-output power of LED chips under the injection current of20mA exhibits11.4%enhancement as compared to the conventional LED chips. However, the forwardvoltage correspondingly increases0.178V. With our proposed micro-structures, the lightoutput power can also be enhanced by8.2%, while the forward voltage increases only0.044V.The optimized micro-structure is helpful for high electric-injection efficiency. This induces ahigh light-output efficiency, and the efficiency droop can be suppressed.A simple maskless wet-etching method was used to fabricate GaN-based LED chips withsurface nano-textured ITO layer. Micro/nano-textured ITO surface with concave pattern orconvex pattern were created by the established techniques of photolithography andwet-etching. Compared to LED chips with flat ITO surface, ITO with nano-textured,concave-hybrid-pattern, and convex-hybrid-pattern exhibit light output power enhancement of11.3%,15.8%, and17.9%，the light output efficiency can be improved by8.8%,13.1%, and13.5%，respectively，under20mA injection current, without the degradation of electricalproperties.