Preparation And Optical Properties Of Silver Film Microstructure For High-efficiency&High-power LED Application

Light-emitting diode (LED), a novel and efficient semiconductor light source, hasattracted more attention. The application of LED is changed from traffic signs andbacklit display to illumination. It is an inevitable trend to develop high-efficiency&high-power GaN-based LED for white light illumination. In this study, in order toovercome the puzzle of not high efficiency of current GaN-base LED, silvernanoparticles were doposited by DC magnetron sputtering and subsequent annealingon the sapphire substrate, on the top of active layer and on the surface of transparentconductive film. The localized surface palsmon of silver nanoparticles can enhancesignificantly the internal quantum efficiency and light extraction efficiency of LEDdevices.The increased transmittances of substrates after depositing silver nanoparticleswere calculated using Rsoft software. The result indicates that the transmittanceenhancement increases with decreasing of diameter of silver nanoparticles. Whenthe diameter is larger than50nm, the transmittance enhancement changes little withthe increasing of diameter. As to the particle with the diameter of50nm, it has thelargest improvement in transmittance when the particles spacing is one time largerthan the diameters.The sputtering experiment result of silver film shows that the deposition rate ofsilver films decreases as the sputtering power decreasing and the deposition ratedecreases with working pressure increasing. When the sputtering power is30W andworking pressure is3Pa, it can be obtained a deposition rate of0.558nm/s for thesilver film. The annealing experiment results of silver films show that the shapes ofthe silver particles change from the strip into spherical or ellipsoidal with increasingannealing temperature and time. The size and shape of the silver particles aredetermined by the thickness of as-deposited silver film. As the thicknesses of silverfilms increase, the diameter of the particles becomes larger after annealing and theshapes change from spherical to ellipsoidal. It can be obtained silver particles withuniform size and distribution can be obtained after annealing at400℃for15min.The reflectivity of sapphire substrate is improved significantly by using silverparticles. When the particle diameter is90nm, the reflectance of the sapphire isimproved by100%at the wavelength of450nm. The Photoluminescence (PL)curves show that the annealed silver film with11.83nm in thickness can increasePL intensity by297%and95%respectively on GZO or AZO layers. The PLintensity is increased by4.76times for LED wafer when the silver particle film isdeposited on the p-AlGaN. When silver nanoparticles are inserted in different layers of LED, the theoretical PL intensity of LED chip can be improved by5.24times. Itwill be have good application prospect for high-efficiency&hight-power LEDfield.