Improvements of P-Electrode Design and Optical Output Power in Deep-Ultraviolet AlGaN LEDs

• Main Authors: Jhih-Yuan Jheng, 鄭智遠
• Other Authors: 武東星
• Format: Others
• Language: zh-TW
• Published: 2018
• Online Access: http://ndltd.ncl.edu.tw/handle/dc2hxw

碩士 === 國立中興大學 === 材料科學與工程學系所 === 106 === In this thesis, the Ni/Au (10/5 nm) films were grown on p+GaN layer by electron beam evaporation. The Ni/Au films were employed as a p-side electrode for the deep-ultraviolet light-emitting diodes (DUV-LEDs). Via the structural design of the p-side electrode, the optoelectronic performances of DUV-LEDs can be improved. Based on the experimental results, it can be found that the formation of an ohmic contact between Ni/Au and p+GaN are mainly affected by the thickness of Ni/Au and the parameters of annealing process for this p-side electrode (such as annealing temperature and annealing time). In this study, the most suitable thickness of Ni/Au electrode is 10/5 nm. Additionally, after annealing in air atmosphere at 500 C for 10 min, the ohmic contact characteristic between Ni/Au and p+GaN can be optimized, where its lowest specific contact resistivity reaches to 2.32×10-6 Ω-cm2. DUV-LEDs with four kinds of p-side electrode design (denoted as 3 fingers-LED, 6 fingers-LED, 9 fingers-LED, and 12 fingers-LED) were fabricated, and the conventional-LED was prepared as a contrasted sample. Besides, the 9 fingers-LED and 12 fingers-LED samples were further fabricated to flip-chip device. Because the emission light with a wavelength of 280 nm would be absorbed by the p+GaN layer, the purpose of this study is to improve the current spreading ability and the light output power of the LEDs through the p-side electrode design. The experimental results indicate that the 9 fingers-LED possessed better optoelectronic performances than those of the LEDs. At injection currents of 20 and 350 mA, the 9 fingers-LED exhibited 154% and 172% enhancements in the output power in comparison to those of conventional-LED, while the improvements in the external quantum efficiency (EQE) were 200% and 198%, respectively. After fabricating the flip chip device, the optoelectronic performances were further improved. At an injection current of 20 mA, the flip chip device possessed 139%, 173%, and 182% improvements in the output power, wall-plug efficiency, and EQE, respectively, as compared with those of 9 fingers-LED. Further increasing the injection current to 350 mA, the flip chip sample can achieve 92%, 71%, and 79% enhancements in the output power, wall-plug efficiency, and EQE, respectively, in comparison to those of 9 fingers-LED. These results clearly indicate that the p-side electrode design is useful for improving the optoelectronic performances of DUV-LEDs.