Toshiba demonstrates technology that doubles the efficiency of LED light extraction with a simple process

Toshiba has developed a technology that can increase the light-emitting efficiency of light-emitting diodes (LEDs) by more than 2 times, and will be displayed on the exhibition board at the international nanotechnology exhibition "nano tech 2006" which opened on February 21, 2006. A concave-convex structure is formed on the surface of the LED chip to improve light extraction efficiency. The doubled here is the result of comparing the LED chips themselves before packaging. By forming a concave-convex structure having a height of 300 nm to 500 nm at intervals of 150 nm to 200 nm in the width direction of the surface of the LED chip, it is possible to prevent light of the light-emitting layer from being reflected by the light-emitting surface. The uneven period and the channel depth in which the light extraction efficiency is improved vary depending on the refractive index of the LED and the wavelength of the light emitted. With the refraction effect of light, it is easy to pass light incident at an angle greater than the critical angle (the total reflection of the incident light). This technology also prevents reflection of light incident at an angle less than the critical angle. The technique of forming the uneven structure by "self-assembly" is a technique of forming the uneven structure by heat treatment and dry etching. The uneven structure is produced by first coating a polymer obtained by combining polystyrene and polymethyl methacrylate on a compound semiconductor by a spin coating method. By performing a heat treatment to "self-assemble", the polystyrene will agglomerate into dots. Usually, the diameter of the spot is only about 50 nm, but it is said that Toshiba has taken some measures to make the diameter reach 100 nm or more. Thereafter, polymethyl methacrylate is removed by dry etching, and the remaining polystyrene is used as a mask pattern for forming a textured structure on the compound semiconductor. Next, in order to form the uneven structure on the compound semiconductor, dry etching is performed again. Finally, the polystyrene is removed using oxygen. This manufacturing method is said to use Toshiba's Patterned Media technology developed for hard disks. Although the company stated that it can maintain the reproducibility of the uneven structure during the research stage, the production of the technology indicates that the reproducibility of the concave-convex structure during mass production and the mass production of the polymer material used as a mask material are somewhat The subject needs to be solved. In addition, the company said that it is not clear about the yield at the time of mass production.