氮化鎵材料之磊晶品質日漸提升，其應用於發光二極體之發光亮度也大幅增高。雖然內部量子效率很高但外部量子效率仍無法有效提升，其乃因光取出效率不佳所致，而影響光取出效率的重要因素之一是平滑表面造成入射光之全反射結果，因此穿透光比例降低。
本論文利用光激發濕式蝕刻對表面p 型氮化鎵做粗糙化處理，並同時避免因乾式蝕刻製程而造成高能離子之表面轟擊損傷效應，進而增加發光二極體之光取出效率及發光強度。
本論文以氫氧化鉀及過硫酸鉀水溶液為蝕刻溶液，氦-鎘雷射為光源。因p型氮化鎵之化學抗蝕特性甚優於n 型氮化鎵材料，故需在表面施加偏壓才得以進行蝕刻，研究結果顯示，當偏壓由4 伏特升高到10 伏特時，蝕刻速率從4.5 nm/min增加到65.15 nm/min。
以光激發濕式蝕刻技術應用於氮化鎵發光二極體之研究結果顯示，以氫氧化鉀/過硫酸鉀水溶液處理後之發光二極體因表面粗糙度變大，使電極金屬與p 型氮化鎵表面之接觸面積變大，而使元件串聯電阻降低，並使電流的注入效率升高。另一方面，經光激發濕式蝕刻處理之後產生表面氧化層，使光折射效率提升，發光二極體其發光強度比乾式蝕刻之標準製程更可提升89 %，而串聯電阻減少25 %。
本研究發現，以磷酸為蝕刻溶液時，雖可使發光強度提升45.5 %，但其與氮化鎵表面之化學反應不同於氫氧化鉀溶液，而使元件之串聯電阻提高77 %且啟動電壓增大，此現象將有待深入解析。

The epitaxial quality of GaN material grows greatly, at the same time, the light output power of GaN-based light emitting diodes increases. Although the internal quantum efficiency is high, there is no obvious increment in the external quantum efficiency owing to the major issue of the poor light extraction. The key factor to affect the light extraction is the total reflection on the smooth surface which resulting in the ratio of incident light passing through surface of LEDs decreases.
Photo-enhanced wet etching is used to roughen the p-GaN on the surface of LEDs in this thesis, and ion bombardment on the surface caused by dry etching would also be avoided. In purpose, the light output power and light extraction will be increased.
KOH and K2S2O8 solution are used and the light source is He-Cd laser. Because of the chemical stability of p-GaN is better than n-GaN materials, a bias should be applied on the p-GaN surface of p-GaN. The results reveal that etching rate increase from 4.5 to 65.15 nm/min with the increase of applied bias from 4 to 10 volt. After the KOH/K2S2O8 solution etching, the series resistance decreases but the incident current efficiency increases due to the roughness of p-GaN and increase of the contact area between the electrode and p-GaN. Because of higher a refractive index of gallium oxide, the output light increase after the treatment. Vertical light output power of the LEDs with photo-enhanced wet etching in K2S2O8 0.065 M and KOH 0.1 M solution increases 89 % (@ 20 mA) and the series resistance decreases 25 %.
In this study, H3PO4 is used as etching solution. The light output power of the LEDs with photo-enhanced wet etching in H3PO4 1 M solution increases 45.5 % and the series resistance increases 77 % (@ 20 mA). However, the turn-on voltage also increases because of a different chemical reaction may take place during etching process.

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