標題: 缺陷能階與量子點之載子躍遷光電容產生機制
The Photo-capacitance Induced by Carrier Transfer between Deep Levels and Quantum Dots
作者: 蔡哲倫
Tsai, Che-Lun
陳振芳
Chen, Jenn-Fang
電子物理系所
關鍵字: 量子點;深層缺陷;載子躍遷;光電容;Quantum dots;Deep levels;Carrier transfer;PhotoCapacitance
公開日期: 2012
摘要: 本論文利用三片樣品分別為2.34ML、3.3ML量子點樣品及砷化鎵基板樣品 之間的比較,透過光性與電性量測分析來瞭解其樣品的光電特性,接著透過光激發下的電性量測觀察樣品中的光電容訊號。由於本實驗室照射光源皆在近紅外光區域,而且小於砷化鎵在室溫下的的能隙,因此優先討論光電容產生的機制;而在樣品2.34ML量子點樣品的低溫光電容圖中,當照光能量在1.3eV附近時,發現有一包明顯的光電容訊號產生,透過和砷化鎵基板樣品在低溫下的光電容相比,兩者在照光1.3eV能量下的光電容趨勢相當類似,因此判斷在2.34ML樣品1.3eV附近的電容值抬升源自於缺陷的貢獻,而為了確認量子點是否有貢獻在光電容上,我們利用量子點載子侷限能力較佳的3.3ML樣品來實驗,藉由改變照光能量的CV圖發現,當照光能量逐漸提升(0.8eV、0.95eV、1.16eV)至可激發量子點基態能量時,CV圖上光電容產生的位置也正好出現在電壓空乏量子點基態的位置,表示量子點的確有貢獻在光電容上;為了釐清量子點樣品當中的光電容來自於缺陷或者是量子點,我們透過調變量測速率實驗證實3.3ML量子點的平台抬升和缺陷有關係,由能帶上的相對位置,我們提出光激發後缺陷能階和量子點間的載子躍遷模型為電子從1.3eV深層缺陷跳至量子點上的能階,因而被量測調變到,並利用照光下的頻率響應佐證我們的論點;而本論文後半段則主要為理論模擬,分成兩部分,第一部分為量子點樣品照光後,只靠量子點本身產生光電容的機制模擬,模擬結果告訴我們由於量子點內正電荷發射時間常數(time constant)的級數小,因此只靠量子點本身要產生明顯的電容值抬升機會並不大,第二部分則是砷化鎵基板樣品的光電容模擬,透過照光量測暫態電容實驗發現無法觀測到樣品內的Optical pump現象,來確認量測到的光電容是否為缺陷發射電子的變化,並藉由缺陷正電荷造成空乏區回縮的模型,模擬出了和實驗趨勢相近的結果。
The electrical and optical properties of 2.34ML、3.3ML quantum dots (QDs) samples and GaAs bulk sample are studied using the photo-capacitance measurements. First of all, we discuss the mechanism of the photo-capacitance illuminated by near-infrared light source. Secondly, according to the photo-capacitance measurements, the deep level traps near 1.3eV exist in both QDs-samples and GaAs bulk sample. In order to investigate how the QDs contribute the photo-capacitance, we measured the 3.3ML QDs-sample with better carrier confinement. The photo-capacitance of 3.3 ML QDs-sample is observed if the illuminating energy is larger than the ground state of the QDs. Therefore, the quantum structure can enhance the photo-capacitance indeed. In addition, if we change the sweeping rate of bias in the C-V measurements, the photo-capacitance in the QDs plateau can be modulated. It means that the photo-capacitance near the plateau of the QDs is related to defects with slow time constant. We establish a model to explain the interaction between the deep level traps and the QDs, and the photo-capacitance is simulated based on the QDs and deep level traps respectively. In summary, the photo-capacitance is caused by the QDs and the deep level traps of 1.3 eV.
URI: http://140.113.39.130/cdrfb3/record/nctu/#GT070052032
http://hdl.handle.net/11536/72673
Appears in Collections:Thesis


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