Performance Improvement of AlGaInP Light-Emitting Diodes with Textured Surface

• Main Authors: Yi-shou Jan, 詹易修
• Other Authors: Chong-yi Lee
• Format: Others
• Language: zh-TW
• Published: 2009
• Online Access: http://ndltd.ncl.edu.tw/handle/27083857557114041293

碩士 === 義守大學 === 電子工程學系碩士班 === 97 === Internal quantum efficiency of a high-quality AlGaInP LED epilayer can approach 99%, but external quantum efficiency is limited due to large refraction index difference between the semiconductor and the outside medium. An example in which light crosses an interface from GaP materials with a refractive index of 3.5 to air with a refractive index of 1 results in a small escape cone with an escape cone angle of 17° for emitted light, representing most total internal reflection light. We have demonstrated improved light extraction from textured AlGaInP light-emitting diodes (LEDs) by using wet etching with a GaP-1 etching solution. The LED properties were characterized by electroluminescence and surface morphology was analyzed by optical microscope and scanning electron microscope. When comparing the textured and the conventional LED, we found that the surface-textured LED exhibits a 25% power intensity improvement at 20 mA. The dominant wavelength variation was under 1% and the voltage variation did not degrade. The output power improvement in the surface-textured LED can be attributed to the formation of surface texture structure at the top GaP surface. This textured surface enabled some light, outside of the escape cone (~17°), to escape through the semiconductor to air interface resulting in additional light extraction. These positive results indicate that high performance AlGaInP LEDs can be achieved by employing a textured surface structure.