Fabrication and Analysis of GaN-based Nanorod Light Emitting Diodes

• Main Authors: Cheng-Yin Wang, 王振印
• Other Authors: JianJang Huang
• Format: Others
• Language: en_US
• Published: 2008
• Online Access: http://ndltd.ncl.edu.tw/handle/40773024305916468594

碩士 === 國立臺灣大學 === 光電工程學研究所 === 96 === Since p-type GaN is well developed in 1990''s, GaN has been widely useded in short wavelength light emitting diodes. Light emitting diodes have advantages such as low power consumption, long life time, good reliability, short response time. Nevertheless, there are still some spaces to improve it like quantum efficiency, peak wavelength shift. A practical approach to fabricate textured GaN-based light emitting diodes (LEDs) by nanosphere lithography is presented. Due to the refraction index difference between GaN and air, there will be a total reflection at this interface and low external quantum efficiency. The current resolution is growing a rough p-type layer on conventional light emitting diodes to reduce the total reflection, but it needs extra time and more cost to do it. By spin-coating a monolayer of SiO2 nanoparticles as the mask, textured LEDs can be fabricated. Both textured p-GaN and textured ITO LEDs show significant improvement over the conventional LEDs without damaging the electric characteristics. The results show that the method is promising for low-cost manufacturing high efficient GaN-based LEDs. The solution for peak wavelength shift is usually treated by growth some nanostructure to release the strain in material. We further use this practical process to fabricate InGaN/GaN multiple quantum well (MQW) LEDs with a self-organized nanorod structure is demonstrated. Contrary to epitaxy, we provide a novel way in fabrication process to solve the peak wavelength shift. Also, because of the hardness of parallel metal evaporation on tips of nanorods without short circuit, there are only a few related results. The nanorod array is realized by using nature lithography of surface patterned silica spheres followed by dry etching. A layer of spin-on-glass (SOG), which intervening the rod spacing, serves the purpose of electric isolation to each of the parallel nanorod LED units. The electroluminescence (EL) peak wavelengths of the nanorod LEDs nearly remain as constant for an injection current level between 25mA and 100mA, which indicates that the quantum confined stark effect (QCSE) suppressed in the nanorod devices. Furthermore, from the Raman light scattering and x ray diffraction analysis we identify a strain relaxation mechanism for lattice mismatch layers in the nanostructure.