本論文探討單層(monolayer)結構之二硫化鉬(MoS2)具有高速和慢速光電導響應段之背後的物理機制。首先由穩態光電流量測可觀察到單層MoS2存在兩種不同的光電流反應時間，慢速段的光電流反應時間皆長於1 s，高速段的反應時間則短於1 ms。進一步透過高頻時間解析光電導量測可發現未處理的(pristine)單層MoS2的光反應時間約在200 s，而經過退火處理的樣品其快速反應段似乎可縮短至約20 s。溫度相依光電導量測可發現退火後的單層MoS2遵循單純的電洞陷阱(hole trap)機制。然而未處理的MoS2樣品其載子活期在低溫卻出現異常的不連續變化，其活期大幅縮短。為了解釋這個異常的現象，我們推測在未處理的MoS2除了電洞陷阱以外，可能存在另一種電子陷阱(electron trap)，會在低溫時縮短電子載子活期。而退火後的樣品因硫空缺的增加，導致電洞陷阱由缺陷能階分裂成缺陷能帶，造成電洞陷阱的活化能下降。這或許可以解釋單層MoS2在退火後具有比較短的載子活期與較快的光電導反應速率。另外在慢速光反應段方面，發現其光電流具有環境相依的特性，真空下光電流會比大氣來的高，此觀察顯示慢速的光電導反應可能與外在的氧氣或水氣的作用有關，遵循氧敏化光電導機制。

The physical mechanisms of the high-speed and low-speed photocurrent response in monolayer MoS2 were investigated. We observed that the high-speed response time are shorter than 1 ms and the low-speed ones are longer than 1 s. The time-resolved photoconductivity measurements indicated that the response time of pristine monolayers are approximately 200 s and the response time of annealed monolayers are decreased to approximately 20 s. The temperature-dependent photoconductivity measurements show that the annealed MoS2 monolayers follow the hole trapping mechanism. Meanwhile a discrete lifetime change was also observed for the pristine sample. Coexistence of the electron trap and hole trap states was proposed to explain the shorter carrier lifetime at lower temperature in pristine MoS2 monolayers. The hole trap level split into a hole trap band due to the formation of high-density sulfur vacancies by thermal annealing was proposed to explain the lower activation energy of hole traps and shorter carrier lifetime in the annealed samples. In addition, we also observed that the low-speed photoresponse is sensitive to the environment. The corresponding photocurrent in vacuum is higher than that in air. This result indicates.

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