Japanese and French scientists use evanescent waves to enhance the brightness of LED

The Japanese and French researchers recently confirmed that the use of V type ridge structure in LED to replace the flat wafer, can make the light extraction efficiency 20 times, the research team have produced the first coupling by evanescent wave (evanescent wave) semiconductor structure to enhance the light extraction efficiency of LED.

Evanescent wave is usually produced in the process of total internal reflection (total internal reflection), which will decay rapidly when it leaves the reflection interface. Total internal reflection (LED) is the main reason to limit the luminous efficiency of optoelectronic devices. In order to increase the overall luminous efficiency, the manufacturers are trying to improve the extraction efficiency and eliminate the total internal reflection. Recently, Japan Industrial Technology Research Laboratory (AIST) Xue-Lun Wang et al using evanescent constructive coupled wave ridge structure, from GaAs quantum wells having a ridge structure to extract the luminance of at least 50%.

Evanescent wave coupling (Evanescent wave coupling)

Wang et al. Used MOCVD to produce the desired structure on the surface of the etched substrate, and measured the photoluminescence of the samples. The results showed that the extraction efficiency was about 50%, which is about 20 times that of the traditional plate structure. With the support of the Paris Institute of nanotechnology, the team confirmed that evanescent waves play an important role in the simulation of physical processes. When the ridge has a width of 0.5 m, the light extraction rate reaches the maximum and decreases rapidly with the increase of the width of the platform.

Wang said that AIST is using this mechanism to create electrically excited LED, and believe that they are the first team to apply the evanescent wave. The British Glasgow University Faiz Rahman is currently committed to the promotion of LED using nano imprint method of light extraction rate, he said the mechanism of AIST using similar acoustic principle, provides an attractive method to enhance the brightness of LED.

Ridged epitaxial structure

Rahman pointed out that the methods of manufacturing AIST substrate structure and other LED research team directly defined pattern in the epitaxial structure is different, and the production of trench substrate (grooved susbtrate) the degree of difficulty will determine the development of this technology in the future. See Applied Physics Letters 94, p.091102 (2009).