在發光二極體(Light emitting diode, LED)中，串聯電阻造成額外的能量損耗並產生熱，為降低串聯電阻值，本論文先建立LED元件電路模型，依據電流擴散路徑，分析總串聯電阻分別為何處所貢獻。本論文發現氧化銦錫(ITO)薄膜的側向電阻以及ITO與P型氮化鎵的接觸電阻加總已超過總串聯電阻的60%，故針對此兩者電阻值作改善。

首先針對不同的ITO鍍膜參數，做電性的改善與探討，包括: (1)不同的鍍膜方式,電子束蒸鍍與射頻濺鍍, (2)ITO鍍膜速率, (3)ITO材料源組成, (4)ITO鍍膜後快速退火的環境氣體、溫度、時間。在電性的量測中，傳輸線元件與霍爾量測分別用來測量特徵接觸電阻以及電阻率。

發現無氧環境能增進ITO薄膜的電性。對電子束蒸鍍ITO而言，電阻率由2.85×10-3 Ω•cm降低至4.52×10-4 Ω•cm，亦使得ITO與P型氮化鎵的特徵接觸電阻下降了一個數量級。對濺鍍ITO薄膜而言，電阻率獲得大幅地下降，由~10-2 Ω•cm降低至~2×10-4 Ω•cm，但濺鍍ITO於P型氮化鎵上仍然是蕭基接觸(schottky contact)。此外，ITO薄膜在蒸鍍速率低於1 A/s展現了較低的電阻率，使用83:17、90:10、95:5(In2O3:SnO2 wt%)三種不同銦錫比例的ITO蒸鍍源展現了相似的電性結果。

將新的ITO電性參數代入LED串聯電阻模型中，得到理論電阻值在3~4 Ω。同時用改良的製程實際製作LED元件，得到面積1×1 mm2的LED串聯電阻值成功由10.4 Ω降至4.5 Ω，與LED模型估計值相符。

In a light emitting diode(LED), series resistance causes additional loss and generates heat. To minimize series resistance, we established a device circuit model that analyzes the individual series resistance attributed to each contact and material along the current path.We found the indium tin oxide(ITO) lateral resistance and the contact resistance between ITO and p-type GaN dominated > 60 % of the total series resistance. Thus process improvement was aimed at reducing these two resistances.

We conducted a variety of experiments on ITO deposition process that include: (1)different methods of deposition--E-beam evaporation vs. RF sputtering, (2)ITO deposition rate, (3)ITO source material composition, and (4)the environmental gas, temperature and time in the rapid thermal annealing (RTA) after ITO deposition. Electrical properties such as specific contact resistance and electrical resistivity were measured by tramsmission line model (TLM) experiment and Hall measurement, respectively.

We found oxygen-free environment enhanced the performance of ITO films. For E-beam ITO, the resistivity was reduced from 2.85×10-3 Ω•cm to 4.52×10-4 Ω•cm and the specific contact resistance was lowered by an order of magnitude. And for sputtered ITO, the resistivity was largely reduced from ~10-2 Ω•cm to ~2×10-4 Ω•cm, but Schottky contact still appeared in between sputtered ITO and P-GaN. In addition, E-beam ITO films with a deposition rate of below 1.0 A/s exhibited smaller resistivity, and films using three different target material compositions: 83:17, 90:10, 95:5 (In2O3:SnO2 wt%) showed similar results.

New ITO electrical parameters were then applied into the device model leading to a prediction of 3~4 Ω total resistance. Simultaneously, improved process was used to fabricate new LED, the series resistance of 1x1 mm2 chips in size was successfully decreased from 10.4 Ω to 4.5 Ω, in agreement with the device modeling.

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