本論文的研究主題在於針對氮化物系列金半金光偵測器設計新穎的元件結構，以期望改善光偵測元件之特性，包括抑制元件漏電流ヽ增加元件速度ヽ效率與響應特性。本論文係使用有機金屬氣相沉積技術於藍寶石基板上成長氮化物磊晶結構，進而製作氮化物系列金半金光偵測器，並進行元件特性量測與分析。
為了使氮化鎵系列金半金光偵測器達到最佳的元件特性,吾人必須設法抑制因氮化鎵晶體與藍寶石基板間之晶格常數與熱膨脹係數不匹配產生的差排缺陷所導致的漏電流。本論文的第一部分即採用低溫氮化鋁覆蓋層及未活化的鎂摻雜氮化鎵覆蓋層來製作氮化鎵紫外光偵測器以解決此一問題。與傳統無覆蓋層的金半金光偵測器相比，藉由加入此一覆蓋層結構可有效降低暗電流值且增加紫外光對可見光之拒斥比。此可歸因於覆蓋層可以提供較大與較厚的蕭基能障，並對半導體表面能態有鈍化的作用。
此外，元件的操作效率與速度亦關鍵性地決定了光偵測器的優劣。基於此原因，我們設計溝槽式電極結構應用於氮化銦鎵金半金藍光偵測器，藉由此一結構設計，可縮短光載子的漂移時間，亦即可提高元件偵測速度與效率。與傳統無溝槽式電極結構的金半金光偵測器相比，使用溝槽式電極結構能大幅提升元件的光響應與光暗電流比，並能增加光偵測器的響應度與外部量子效率。

The objective of this research is to design the appropriate device structure for nitride-based metal-semiconductor-metal (MSM) photodetectors to improve the device performances, including the suppression of the dark leakage current or the enhancement of speed, efficiency, and photoresponse of the photodetectors. The structure of nitride-based MSM photodetectors were epitaxied on sapphire substrate by metal-organic chemical vapor deposition system (MOCVD). The fabrication and characterization of the MSM photodetectors were also employed in our experiments.
To achieve a GaN-based high performance MSM photodetector, it is critical to reduce the leakage current, which result from the defects in the film. However, the large differences in lattice constant and thermal expansion coefficient between GaN and sapphire inevitably lead to high dislocation defect density in the GaN epitaxial layer. We adopted a low-temperature (LT) grown AlN or an un-activated Mg-doped GaN capping layer onto the GaN active layer to solve this problem. Compared with conventional MSM photodetectors, we effectively suppressed dark leakage current and achieved larger UV to visible rejection ratio from the photodetectors with LT-AlN or an un-activated Mg-doped GaN capping layer. This result could be attributed to the thicker and higher potential barrier and effective surface passivation after inserting LT-AlN or an un-activated Mg-doped GaN capping layer.
On the other hand, the efficiency and speed of the photodetectors are key points to judge the detectors between good and bad. For this reason, we designed the recessed electrodes configuration to reduce the transit time of photogenerated carriers and enhance the efficiency and speed of InGaN-based MSM photodetectors. From device measurement results, it was found that measured photocurrent and photocurrent to dark current contrast ratio were both much larger for the MSM photodetectors with the recessed electrodes. The responsivity and external quantum efficiency of the detector with recessed electrodes were also found to be larger than conventional one.

Chapter1

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Chapter2

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Chapter3

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Chapter 4

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Chapter 5

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