本論文著重探討二氧化錫(tin oxide, SnO2)奈米線之光電導特性與其傳輸機制。在計算光電導增益(photoconductive gain, Γ)的部分，我們可透過3.0 V的低偏壓便量測出二氧化錫奈米線其光電導增益值可達8x10^8，此數值為目前探討光電導效率之文獻研究的最高值。利用歸一化增益(normalized gain, Γn)去除元件特性上的實驗參數影響，二氧化錫奈米線其最高歸一化增益值可達20 cm^2/V，約略大於氧化鋅，二氧化鈦，三氧化鎢等高效率金屬氧化物光導體約一至五個數量級。
利用功率相依之光電導量測求得載子活期，從奈米線其歸一化增益與載子活期分別敏感於光強的關係，確認長的載子活期為主要導致高歸一化增益值的因素。同時驚訝地發現包含二氧化錫，二氧化鈦，三氧化鎢這類具有高光電導效率之金屬氧化物奈米線其量子效率只有1%左右甚至是遠小於1%，這數值小於傳統塊材或薄膜約一至三個數量級。為解釋此現象，於是藉由奈米線所存在的表面空乏區(surface depletion region, SDR)以及表面主導之光電導機制，來解析在奈米線中為何存在異常低的量子效率及其功率相依效應。除此之外，利用材料具有不同的本質特性如載子活期，載子濃度與介電常數等，進而解釋不同金屬氧化物奈米線當中本質光電導效率的差異。

In this thesis, We report on the superior photoconduction (PC) efficiency and the dynamic study of the wide-bandgap single-crystalline tin dioxide (SnO2) nanowires (NWs). The photoconductive gain of the single-wire device can go up to 8x10^8 at a low bias of 3.0 V, which is the highest reported value to date for the single nanostructure photodetectors. Especially, the optimal normalized gain with the physical meaning of intrinsic PC efficiency of SnO2 NWs reaches 20 cm^2/V, which is over one to five orders of magnitude higher than the other highly efficient metal oxide semiconductor NWs such as ZnO, TiO2, and WO3.
The time-resolved PC measurement shows that the carrier lifetime with sensitive power dependence is the dominant factor determining the PC efficiency for the superior NW group. In addition, the numerical analysis surprisingly indicates that the metal oxide NWs reveal extraordinarily low (effective) quantum efficiency in common, which is one to three orders of magnitude lower than the conventional films counterparts. The presence of a very narrow surface depletion region with only a few nanometers width for the generation of long-lifetime carrier is proposed to explain the abnormal quantum efficiency and its power dependence. The study provides new understanding to the difference of intrinsic PC efficiency and the nature of “surface photoconductivity” between the metal oxide semiconductor nanostructures.

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