本論文旨在針對氮化鎵系列發光二極體進行垂直結構化設計，以提昇氮化鎵系列元件之電特性、發光效率。我們提出一種利用電鍍鎳（Nickel electroplating）及雷射剝離（Laser Lif-Off）技術，應用於氮化鎵發光二極體之垂直結構化，可以達到減少元件內部電流擁擠效應及降低串聯電阻的作用，進而提升發光效率。對於垂直元件結構之表面更進一步進行適當之蝕刻處理，改變元件表面形狀，促使電流路徑電阻均勻化，使元件內部之電流或發光分佈更均勻。
首先，提出利用非等向雷射蝕刻（Anisotropic Laser Etching）漸變表面磊晶層厚度結合透明導電層（Transparent Conductive Layer, TCL）之方法，以達到電流及發光分佈均勻化之目的，經由ISE-TCAD二維模擬證實發光二極體之主動區（Active region）電流及發光均勻分佈皆有顯著提升，實驗完成之元件所量測得到之光輸出功率（Light output power, Lop）較一般垂直發光二極體提升了26%～38%，利用近場光電分析（Near field electron-luminance analyzer）發光均勻性也遠較一般垂直發光二極體好。
其次，再提出製程簡單、成本低廉、及可以整批處理之非等向ICP蝕刻成單階步梯表面（Mesa surface）結合TCL同樣用於達到電流及發光分佈均勻化之目的。因IZO/Ti與n-GaN接面具有良好之歐姆接觸特性，又因其光穿透性佳應用於加強電流擴散之TCL，然IZO與n-GaN接面則為具有單向導通之蕭特基接觸（Schottky contact）特性，可應用於電流遮蔽。據此，我們採取局部性的Ti蒸鍍，使n-GaN外圍表面形成歐姆接觸特性之IZO/Ti與n-GaN接面；陰極下方則使形成蕭特基接觸特性之IZO與n-GaN接面，藉由其遮蔽逆向電流之功能，將陰極下方大電流遮蔽，搭配元件外圍單階步梯表面結合TCL將電流均勻擴散，提升了25%光輸出功率。

Devices with a vertical structure would allow a much large power handling capability due to the immune of current crowding effect. In this dissertation, Vertical-conducting Metal-substrate GaN-based Light-Emitting Diodes (VM-LEDs) were fabricated by using of nickel electroplating substrate transformation in conjunction with laser lift-off (LLO) technique. To equalize the resistance of all possible current paths in the fabricated VM-LEDs to release current crowding effect, the surface structures onto n-GaN were designed and fabricated for enhancing the uniformly distributions of current and light emission.
A graded TCL/n-GaN surface structure on 40-mil VM-LEDs for improving light emission uniformity and light output power is proposed and demonstrated. The feasibility of the proposed scheme was verified by current and light emission distribution as well as light extraction rate simulations. In conjunction with a nonuniform excimer laser beam irradiation through a mask and rotation of the epitaxy wafer, VM-LEDs with a concave-surface n-GaN layer were also successfully fabricated. Typical improvement in light output power by 26~38% at an injection current of 350 mA as compared to the one without anisotropic etching has been obtained. The LEDs based on the graded TCL/n-GaN surface structure has been shown providing a significant improvement in light output power (Lop) and much more uniform in current and light emission distribution as compared to those of regular VM-LEDs.
A novel scheme using patterned Ti deposition associated with a transparent IZO layer is further proposed for current blocking and spreading of VM-LEDs. An anisotropic mesa etching on the surface layer (n-GaN) of the VM-LEDs associated with the IZO TCL is also proposed to further release CCE of the device. In experiments, VM-LEDs with the proposed structure have been successfully fabricated and an average improvement in light output power by about 25% at an injection current of 350 mA as compared to that of regular VM-LEDs has been obtained.

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