透過光電化學蝕刻方式進行表面粗化以增加發光二極體之亮度

Abstract

本論文將著重在光電化學蝕刻在氮化鎵上的特性探討和在發光二極體上的應用，特性分析包括氫氧化鉀濃度, 過硫酸鉀濃度, 偏壓大小等變因對其之影響。對於氫氧化鉀濃度而言，蝕刻速率主要受限在濃質擴散速率和水合反應所造成峰值速率的影響，過硫酸鉀在鹼性溶液中所產生的激進分子將有利於蝕刻反應中的氧化反應的進行，偏壓在此扮演的角色是改變氮化鎵其表面的能帶方向，且其產生電洞井將有助於蝕刻速率的提升，氮化鎵上的金屬阻擋層能增進UV光所產生的電子電洞對，但也會造成非均勻的蝕刻表面，可透過高偏壓方式來解決，磷酸溶液的蝕刻機制一樣受限在濃質擴散速率和水合反應的影響，蝕刻後的表面型態決定在光反應和電反應競爭後的結果。

經過光電化學蝕刻處理過後的發光二極體，其漏電問題歸因於多層量子井旁側壁遭蝕刻損傷所導致的漏電路徑。而粗化處理後所增加的亮度約為1.1至1.3倍，也約等於電力轉換光能所增加的值，光電化學蝕刻是個簡單且不需複雜的設備的製程，蠻適合做氮化鎵為基礎的發光二極體表面粗化的製作

In this thesis, a photoelectrochemical wet etching process has been discussed. The etching rate is mainly dominated by diffusion-limited and hydration effect about KOH concentration. The peaking effect in the PEC etch rate is analyzed by a hydration model. The chemical mechanism of the S2O82-/OH- etching of GaN as been found to involve either sulfate radical ions or hydroxyl radicals. Vary the direction of the band diagram by applying bias voltage can form a potential well for holes at surface and enhance the etching rate. The metal mask can enhance the etching activation but also cause non-uniform etching surface morphology. The non-uniform problems can be solved by applying higher bias voltage due to its high electric field. PEC etching in H¬3PO4 solution is also controlled by diffusion-limited and hydration effect. The morphology after PEC etching is the result of competing between photo-assist and bias-assist etching. The leakage current of LEDs with PEC etching slightly increases owing to the damage of sidewall. The roughening treatment resulted in an increased of light output by a factor of 1.1~1.3 and the factor approximately equal the ratio of the luminance to electric power. The PEC etching technique is simple and does not require complicated process, implying that it will be suitable for manufacturing of GaN-based LEDs with surface roughening.