InGaN-based Light Emitting Diodes with Imprinted AC Bias-Assisted Photoelectrochemical Oxidation

• Main Authors: Ya-Yu Yang, 楊亞諭
• Other Authors: Wei-Chi Lai
• Format: Others
• Language: zh-TW
• Published: 2009
• Online Access: http://ndltd.ncl.edu.tw/handle/12880713547147293580

碩士 === 國立成功大學 === 光電科學與工程研究所 === 97 === In this work,we developed a novel and low-cost oxidation process for growing gallium oxide on GaN in water. This process combines alternating (AC) bias-assisted photoelectrochemical (PEC) oxidation with imprint technique, which can grow and pattern gallium thin film by an ITO-coated molds. Because of the low refractive index (n=1.8-1.9) and high dielectric constant contrast to GaN, gallium oxide is suggested to reduce the internal reflection and to increase light escape from the surface of the GaN-based LEDs. Here, we performed mesh-oxide LEDs by the novel process and investigated their optoelectrical characteristics. The Ni-Au contact characteristic of p-type GaN with and without PEC oxidation was studied in this work. After thermal annealing in 550 OC for 5min in O2 ambient in furnace, both of the two samples have specific contact resistances of 1.68×10-3 and 7.85×10-2 Ω-cm2,respectively. In the optoelectrical characteristics of LEDs, we performed the oxide LEDs with the same oxide thickness of 40nm to study further. The forward voltage (Vf) was increased by 0.11~0.22 V in the oxide LEDs, and the light output power of LEDs at 20mA were between 3.0 mW and 3.14 mW which were 17.2%~22.7% higher than the conventional LED. The decrease of leakage current was also observed in the mesh-oxide LEDs. Because of decrease the area for Ni/Au TCL as compared to the conventional LEDs, and the oxidized region tends to effectively cover or suppress threading dislocation located at the top surface of the mesh-oxide LEDs. The improvement on light output power can be attributed to the PEC grown convex oxide layer with nano-rough morphology, resulting in uniform current spreading by mesh TCL. The change in the intermediate refractive index of the oxide film can reduces the total internal reflection at the GaN surface, then make light escape out of the surface of LED more efficiently.