Study Of Luminous Efficiency Of Blue GaN-LED Chip On Si Substrate

In resent years,the development of GaN-LED is rapid.But its cost and luminous efficiency are the main problems in wide application in lighting area. GaN-LED on silicon substrate has attracted much attention for its low cost.But the research on its luminous efficiency is still in initial stage now.The topic of this paper is the improvement of luminous efficiency of GaN-LED on silicon substrate.The research is based mainly on two methods including anti-reflection of LED and wet roughening.Some innovative results are achieved as following;1.Wet roughening is also one of effective methods to improve the luminous efficiency of GaN-LED chip on silicon substrate.The wet roughening mechanism is the polarity selection mechanism;N-polar GaN is etched more easily than Ga-polar. A1N have the same etching mechanism as well.The light-escape layer of LED chip on silicon substrate is N-polar AIGaN.The surface of A1GaN layer was wet roughened by KOH solution in this paper.After the chips were roughened in different times,SEM pictures show that many hexagonal pyramids emerge on the surface.The compare between roughening chips and non-roughening chips in the optical and electrical parameters were measured by Electroluminescence measure system.The results indicate that roughening could improve the luminous intensity of LED chips without declining their electrical performances.Moreover the luminous wavelength of LED chips is blue shift after roughening because of the relaxation of stress field.During PEC-roughening experiment,the results show that light source of Xe lamp is helpful for the roughening process.The PEC-roughening LEDs have higher density of hexagonal pyramids on the surface than the common roughening LEDs.And increase rate of luminous intensity of LED chips is higher by PEC-roughening.2.For the high transmittance and chemical stability,ZnO film was chosen as anti-reflection film in GaN-LED on Si substrate in this paper.First of all,ZnO films were deposited on glass substrates by magnetron sputtering.The crystal quality, morphology and roughness,transmittance spectrum of ZnO films were measured by Stylus Profiler,XRD,AFM and spectrophotometer in order to find out the optimum sputtering condition.Among ZnO films prepared in different sputtering powers,the film in 150W has the best crystal quality,lowest roughness and highest transmittance in visible wavelength region.Fixing 150W sputtering power,ZnO films were prepared in different Ar/O₂ flow ratio.The result suggests O₂ could improve the crystal quality and roughness of ZnO film.When Ar/O₂ flow ratio equals 2,the film has the best crystal quality,lowest roughness and highest transmittance in visible wavelength region.3.As anti-reflection coating,ZnO film was deposited on the top of blue GaN-LED on Si substrate by magnetron sputtering in the optimum sputtering condition and its thickness wasλ/4(about 117nm).The distributions of luminous intensity,main wavelength,forward voltage and leakage current of LED chips were measured by electroluminescence measure system.The results show that ZnO anti-reflection coating can improve the luminous intensity of chips appreciably.On the other hand,ZnO anti-reflection coating doesn't change forward voltage and leakage obviously.This work were supported by 863-project of China and electronic develop fund of MⅡ.