GaN基藍光發光二極體(Light Emittering Diode, LED)自1990年代中期由日本日亞化公司的中村修二研究員開發成功後，即成為一熱門研究題材，LED具有體積小、壽命長、操作反應速度快、省電、可靠度高、不易破損、應用範圍廣且無熱輻射與水銀有毒物質污染等優點，其與螢光粉或利用RGB三原色LED組合形成之白色光源，於未來照明市場上極富應用潛力。此一”新世代光源”若要取代日光燈管，首先要面對的問題主要在於製作大面積、高效率藍光LED元件與解決傳統藍寶石(Sapphire)基板不導電、導熱不佳缺點等方面。本論文提出以區塊雷射剝離技術(Patterned Laser Lift-off)置換藍寶石基板，並於載子濃度受限制的n-type GaN磊晶層上濺鍍具透明導電銦鋅氧化物 (Indium-Zinc-Oxide, IZO)作為電流擴散層(Current Spreading Layer)，製作40 mil大面積、高亮度垂直結構LED，以解決傳統GaN基LED包括元件散熱不良、電流分佈不均、低流明通量與發光不均等諸多方面的問題，期望可對新世代LED光源之開發提供助益。
本論文於LED研發製程配合電鍍鎳技術並使用248 nm的KrF準分子雷射，可迅速於10分鐘內完整反應解離2吋直徑藍寶石基板，成功地將在藍寶石基板上有機金屬化學氣相沈積系統(Metal Organic Chemical Vapor Deposition, MOCVD)所沈積之GaN磊晶薄膜置換至電鍍鎳基板上。據材料分析及光電特性量測結果顯示，磊晶主動層(Active layer)並未因雷射照射加工而造成元件特性破壞，令人振奮的，本研究所研製之垂直結構金屬基板LED之光電特性遠勝於傳統水平結構藍寶石基板元件。
於垂直結構GaN基藍光LED之製程中，我們提出包括在雷射剝離後利用ICP乾蝕刻以增加n-GaN層表面載子濃度，沉積非合金薄金屬鈦(25 Å)作為與n-GaN界面歐姆接觸，再濺鍍一透明導電的IZO薄膜，降低元件順向偏壓與串聯電阻，以達到電流均勻分佈與增加光輸出功率。實驗結果顯示，於350 mA工作電流條件下，40 mil-LED元件順向偏壓比傳統元件降低0.3 ~ 0.5 V，光輸出功率甚至可比傳統者增加97%，且其串聯電阻均較傳統平面式元件降低60%以上，且光電轉換效率可提升108%。本研究結果顯示使用金屬基板所製得垂直式元件之光電特性遠較傳統橫向結構LED優異，不僅可降低能源的耗損，於大電流、高功率之工作條件下，其可靠度也將大幅提升。

In the mid-1990s, nitride-based material was first successfully grown on sapphire by Shuji Nakamura of Nichia co. using Metal Organic Chemical vapor deposition (MOCVD) technology. Up to now, lots efforts have been made in the promotion of light extraction and efficiency of blue GaN-based LEDs. Owing to its advantageous of small volume, long life, fast responding time, low power consumption, lasting, better quality of reliability, smaller flexible lighting fixtures, intrinsically safety, and no mercury added, a novel solid-state white lighting source, so called " new generation lighting source " has been proposed using blue GaN-based LEDs and yellow phosphor powder or direct combination of lights emitting from RGB color LEDs. However, challenging issues of GaN-based LEDs including poor light conversion efficiency and poor thermal conducting caused by the sapphire substrate, and non-scalable light output with respect to the chip size, etc., are still open questions.
This thesis aims to tackle the challenging issues of present GaN-based LEDs. Various methods including replacing the sapphire substrate with an electroplating substrate by patterned laser lift-off (patterned LLO) technology, depositing a sputtered-Indium-Zinc Oxide film as a current spreading layer atop n-GaN layer for the fabricating of 40 mil-high power vertical-structured metallic GaN-based LEDs (VM-LEDs) were proposed. Using a KrF excimer laser (248 nm) and nickel electroplating, it takes about 10 min for the transfer of GaN epi-layer from 2” sapphire substrate to Ni substrate with an acceptable yield(>50%). According to the material analysis and optoelectronic characterizations, the measured optoelectronic performances of VM-LEDs reveal a great improvement as compared to that of conventional lateral-structured LEDs.
In experiments, the use of inductive coupling plasma (ICP) dry-etching to increase the carrier concentration of n-GaN layer and sputtered-IZO as a transparent conducting layer to enhance current spreading was demonstrated and discussed. As compared to regular-LEDs under an injection current of 350 mA, the series resistance of VM-LEDs was lowered by about 60% and forward voltage drop was also decreased by 0.3 ~ 0.5 V, and the increase in light output power (LOP) is about 97% have been obtained. It is expected that the use of LLO in conjunction with Ni substrate and optimum-thickness IZO TCL would make possible the fabrication of VM-LEDs with even larger area, higher power and better efficiency.

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