| Summary: | 碩士 === 國立成功大學 === 微電子工程研究所碩博士班 === 95 === Recently, the light output power of light-emitting duodes (LEDs) was enhanced due to the rapid development of epitaxy technique. As a result, a high internal quantum efficiency of around 90% has been achieved for AlGaInP LEDs. However, the absorbing and poor thermal conducting of conventional GaAs substrate have hindered the further application for large area, high power, and high-efficiency illumination.
This thesis aims to tackle the challenging issues of present AlGaInP LEDs. Various methods including replacing the GaAs substrate with a selective Ni electroplating substrate by chemical wet-etching technology, depositing a transparent conducting layer atop n+-GaAs layer for the fabricating high power vertical-structured metallic substrate LEDs were proposed.
The proposed metallic substrate AlGaInP LEDs structures included n-side up abd p-side up devices, and the n-side up LEDs with a meshed Indium-Zinc Oxide (IZO) film as current spreading layer (CSL) were also fabricated. Moreover,
As compared to regular-LEDs under an injection current of 20 mA, the series resistance of metallic substrate AlGaInP LEDs was increased by about 60% and forward voltage drop was also increased by 0.1�{0.2 V. Note that thermal annealing would account for stress at interface of the Nickel-plating substrate and epi layer for n-side up structure, resulting in the reducing of conductivity of Nickel substrate and thus the increase in series resistance of n-side up LEDs. However, the light output power (LOP) of p-side up LEDs was enhanced by about 103.2% (i.e. �尊OP/LOP) under an injection current of 20 mA. It could be attributed to the use of high reflector layer and avoidance of thermal stress. Furthermore, the n-side up LEDs with an IZO CSL shows an increase in LOP by about 116.7% at 20 mA, as compared to regular-LEDs. It is expected that the improvement of Nickel thermal stress and the use of IZO CSL with optimized design could further improve light power of metallic substrate AlGaInP LEDs and would be very promising for the fabrication of high power LEDs.
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