Investigation of High-Brightness GaN Light-Emitting Diodes with Copper Substrate

• Main Authors: Kuo-Wei Yen, 嚴國瑋
• Other Authors: Ray-Hua Horng
• Format: Others
• Language: zh-TW
• Online Access: http://ndltd.ncl.edu.tw/handle/63474241456853741557

碩士 === 國立中興大學 === 精密工程學系所 === 95 === In general, the structure of GaN light-emitting diode is commonly epitaxially grown on sapphire substrate. The large joule heat is generated from the active layer during high current injecting. That could degrade the performance of device because the low thermal conductivity of sapphire substrates. To solve this problem, GaN epilayer will be transferred to the copper substrate by electroplating. The copper substrate supplies high electrical conductivity and thermal conductivity. In this study, a vertical conductive type structure for GaN/mirror/Cu LED combined with laser lift-off (LLO), Ni/Ag mirror with high reflectivity (about 92%), and electroplating technique are demonstrated. The Ni/Ag was deposited on the p-GaN layer and then electroplated by copper substrate. Following, using NaOH solution roughens the n type GaN cladding layer after LLO. The epitaxy structure is separated by LLO from the sapphire substrate to fabricate p-side down device. The forward voltage (@20 mA) of the GaN/mirror/Cu LEDs and conventional LEDs are 2.63 V and 2.74 V, respectively. The forward voltage (@350 mA) of the GaN/mirror/Cu LEDs and conventional LEDs are 3.88 V and 3.94 V, respectively. From these results, the GaN/mirror/Cu LEDs decrease the series resistance in a vertical conductive structure due to the large-area metal being ohmic to p-GaN and n-GaN providing well current spreading. The leakage currents (@-5 V) of GaN/mirror/Cu and conventional LEDs are 90.2 nA and 47.8 nA, respectively. The luminance intensity of GaN/mirror/Cu LEDs with textured surface is better than that of conventional LEDs. It is about 4.6 times. With injection current to 1 A, the light output power of GaN/mirror/Cu LEDs could be linearly increased. It is due to the copper providing a good conductivity and heat sink.