Investigation of the reflective electrode metal pad on Hole Structure Current Blocking Layer in GaN-based light emitting diodes

• Main Authors: Chou, Li-Chung, 周立中
• Other Authors: Kuo, Cheng-Huang
• Format: Others
• Language: zh-TW
• Published: 2014
• Online Access: http://ndltd.ncl.edu.tw/handle/39pvx4

碩士 === 國立交通大學 === 光電科技學程 === 102 === In this study, the adhesion of the n and p reflective electrode (Cr/Al/Cr/Pt/Au) on GaN-based light-emitting diode (LED) was investigated. The application of a hole structure on the current blocking layer (CBL) and the transparent conductive layer (TCL) predictably enhanced the adhesion between the reflective electrode and the GaN-based LED. The effect of different hole structures on GaNLED optoelectric characteristics was also analyzed. We initially fabricated the normal structure GaN-based LED, which resulted in the CBL hole structure GaN-based LED. We used the CBL hole structure to enhance the adhesion between the reflective electrode and the GaN-based LED. According to the experimental results, the probability of pad peeling rate was reduced from 10% to 5.5%. Subsequently, the two structures were applied to GaN-based LEDs with chip sizes of 500×250 μm2 and 950×950 μm2. With injection currents of 20 and 350 mA, the light output power of the CBL hole structure was attenuated compared with the normal structure at 1.76% and 1.97% respectively. It’s attributed that the effect of the hole structure on the device’s current spreading status. Furthermore, we fabricated the TCL hole structure to enhance the adhesion between the reflective electrode and the GaN-based LED. In accordance with the experimental results, the probability of pad peeling rate was reduced from 10% to 4%. Then, we applied the TCL hole structure to GaN-based LEDs with chip sizes of 500×250 μm2 and 950×950 μm2. With injection currents of 20 and 350 mA, the light output power of the TCL hole structure was attenuated compared with the normal structure at 1.71% and 0.7% respectively. It’s attributed that the effect of the hole structure on the device’s current spreading status. Finally, we fabricated the CBL&;TCL dual-layer hole structure to enhance the adhesion between the reflective electrode and the GaN-based LED. In accordance with the experimental results, the probability of pad peeling rate was reduced from 10% to 0%. These results reveal a successful solution to the poor adhesion of the reflective electrode. Subsequently, we applied the CBL&;TCL dual-layer hole structure to GaN-based LEDs with a chip size of 500×250 μm2 and an injection current of 20 mA. The light output power of the CBL&;TCL dual-layer hole structure was enhanced compared with that of the normal structure at 1.38%. It’s attributed that the 36.58% increase in direct reflection of the CBL&;TCL dual-layer hole structure of the light area by the p-type reflective electrode. This entire light-emitting area accounted for 2.25%. This structure was then applied to GaN-based LEDs with a chip size of 950×950 μm2 and an injection current of 350 mA. The light output power of the CBL&;TCL dual-layer hole structure was attenuated compared withthat of the normal structure at 4.51%. Analysis showed the reasons for the attenuation of light output power by the CBL&;TCL dual-layer hole structure. The reasons are as follows: 1. poor design of mask pattern; 2. increase in device size results in longer light transmission path, which indicates the probability of smaller light escaping from the device; 3. the hole structure affects current spreading status in the device; and 4. poor epitaxy wafer. In summary, the CBL&;TCL dual layer hole structure can successfully enhance the adhesion between the reflective electrode and the GaN-based LED to solve the practical application of reflective electrodes.