Increase of Light Extraction Efficiency of GaN-based Light Emitting Diodes by Nanosphere Lithography

• Main Authors: Cheng-hsiu Lin, 林誠修
• Other Authors: Yen-kun Su
• Format: Others
• Language: en_US
• Published: 2008
• Online Access: http://ndltd.ncl.edu.tw/handle/07054137868744108863

碩士 === 國立成功大學 === 光電科學與工程研究所 === 96 === In conventional GaN light-emitting diodes (LEDs), the external quantum efficiency is low because only small fraction of photons which generate inside of GaN-based LEDs can escape. Due to the big difference of refractive indices between GaN (n=2.5) and air (n=1), the critical angle at which light generated in the InGaN/GaN active region can escape is approximately 23° [ ]. To improve the light extraction efficiency, photonic crystal (PC) structures have also been investigated. A PC is a periodically repeating structure comprising two materials with different dielectric constants. To fabricate PC structure light emitting diodes, nanosphere lithography (NSL) is a well-known, low cost and quick preparation method. In this investigation, the PC structures on p-GaN and sidewall region are successfully fabricated on GaN based light emitting diode. The diameters of nanospheres are 500 and 300 nm, respectively. An ordered monolayer Polystyrene spheres are uniformly spread on p-GaN surface and sidewall region by spin coating. The PC structures are formed by inductively coupled plasma (ICP) dry etching. As the result, with 20 mA injection current, it was found that the output power were enhanced by 15.08% and 14.36% for the p-GaN pc LEDs and n-GaN sidewall textured LEDs, respectively. The enhancement is attributed to the light extraction probability of internally reflected photons.