| 摘要: | 我們利用多能階的Anderson模型來模擬由單一量子點與電極所構成之.位障糸統。流經基態與激發態之穿隧電流在軌域穿隧及軌域佔據的不同情況可利用非平衡態格林函數法來求取。.能階的穿隧電流電壓特性曲線証明電子佔據數影響每一個共振穿隧能階(源自電子庫倫交互作)的機率。本研究最終的目地是導出流經量子點任意能階的穿隧電流的公式，以便幫助實驗者來理清分子電晶體及單電子電晶體所測得之電流電壓特性曲線。我們想建構一量子點元件同時有單光子檢測及單光子放射兩種功能。該元件之動態特性可利用非平衡態格林函數法來理清。該元件設計之概念如下：入射之單光子會在量子點生成exciton的共振能階。因電子與電洞相互吸引力，會使得源極電子在較低電位的情況即可穿隧過量子點。這也意味.，一旦量子點沒有檢測到光子，源極電子須較高的偏壓才能穿隧過量子點之共振態。因光電流與暗電流的比值可以很大，因此具傋高敏度量測單光子的功能。為了具傋單光子放射功能，除了兩個n型電極之外，將加入p型電極以便操控量子點之電洞能階。在這研究計畫，前二年我們分別探討流經量子點的靜態與動態的穿隧電流。最後一年我們理論性地討論在源極裡的電子如何穿隧進入一個運動中的量子點。具有四個氮基之DNA在圓柱狀管中流動可以被視為運動中的量子點。DNA是由延.圓柱狀管子方向之電場導入圓柱狀管子(DNA帶負電)，DNA的流速取.於縱向電場的大小。為了檢測DNA的排序，圓柱狀管將罝放於源極與汲極之們。來自源極電子穿隧過DNA分子(G,A,T,C)之穿隧電流可以用來決定DNA的分子排序(所謂基因密碼)。 (1) Within the first year We have employed the multi-level Anderson model to simulate the system of the tip/quantum dot (QD)/substrate double barrier junction. The tunneling current through the ground state and the excited states in the cases of shell-tunneling and shell-filling is theoretically investigated in the framework of nonequilibrium Green's function technique by solving the multi level Anderson model properly. Our current-voltage curves of two-level model show that single-particle and two-particle occupation numbers significantly influence the probabilities of each resonant energies arising from the intralevel and interlevel Coulomb interactions. Our final goal of this study is to develop the general formula of tunneling current through a single quantum or molecule which can be applied to molecule transistors and single electron transistors. Keywords: Quantum dot, Coulomb interactions, single-electron transistors, Keldysh Green function method. (2) Within the second year We attempt to propose a quantum dot device that can be used either as a high-sensitivity single-photon detector (SPD) or a light-emitting single-electron transistor (LESET). The dynamic properties of such quantum dot (QD) devices are theoretically studied by using non-equillibrum Green's function method. The above devices are based on that an incident single photon generates an exciton in the QD, which in turn triggers the tunneling current due to the lowering of electronic levels in the QD by the attractive electron-hole interaction. The detection efficiency of such a device will be estimated, and its advantages over other similar devices are discussed. Vice versa, it can be used as a LESET with high amplification. Keywords: Single-photon detector, exciton complex and time-dependent Anderson model (3) Within the third year In the previous two years time-independent and time-dependent charge transport through a single quantum dot embedded in a matrix is investigated, the position of quantum dots are fixed. We attempt to study the charge transport through a moving quantum dot in the third year. For example, the role of DNA is regarded a moving quantum dot in the case of DNA molecule (A,T,G,C) flowing into a nanopore. DNA molecules are pulled into a nanopore by the longitudinal electric field, the velocity of DNA molecules are tuned by the magnitude of longitudinal electric field. To examine the sequence of DNA, such a nanopore is put between the source and train electrodes. In principle, the tunneling current arising from electrons of the source electrode tunneling through a moving DNA can be used to identify the sequence of DNA. 研究期間：9608 ~ 9707 |
