The luminous efficiency of LED is a main factor to measure whether the photoelectric convertor is efficiency. How to improve the luminaries efficiency. This article introduces effect way to improve the luminaries efficiency of LED from flip chip technology.
Using the MOCVD Technology develops the GaN-based structural layer of LED on the substrate of sapphire, the light issued by the P/N junction light emitting area passes through the upper P Area.Because the conduction properties of P type GaN is not well, in order to get good current expending, there is a need to form a metal electrode layer consist of Ni-Au on the surface of P Area using the vapor technology. The lead of P Area through the metal film extracts. In order to get good current expending,Ni-Au metal electrode layer can not be too thin.Therefore, the luminous efficiency of device would be greatly influenced. Usually, we should considerate the two factors of current expansion and luminous efficiency. But in any case, the exist of metal film can make the light transmittance become worse. In addition, the exist of lead solder joint also influences the light transmittance of device.
Using the structure of GaN LED flip chip can eliminate the above problems fundamentally. Because the chip flips in Si based pad,LED light emitted directly through the sapphire, without the above Ni-Au metal film and lead solder joint,therefore, the light emitted with no loss. The following P-GaN layer is plated with Ag reflective film, which further enhance the emergent light intensity. The experiments point that the quantum efficiency of flip chip power LED devices is 1.6 times higher than the ordinary type device during the peak wavelength region of 450~530nm.