| Summary: | 碩士 === 國立臺灣科技大學 === 電子工程系 === 101 === 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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