本研究將討論流經量子點之高簡併態的穿隧電流。我們想檢驗此穿隧電流是否會出現雙穩態效應。此效應在記憶體元件設計應用是重要的。在量子井雙位障系統，金屬二氧化矽介面及高分子金屬介面都有雙穩態現象。非線性穿隧電流的機制源於電子與電子的交互作用。然而，到目前實驗上沒有報導單電子電晶體可以具有此非線性穿隧效應。理論上的預測仍有不少爭論。例如，有研究宣稱單電子電晶體要有雙穩態，必須電子與電子間的交互作用是負的。單電子電晶體的量子點如果具傋高簡併態，電子占據數(electron occupation number)可能具傋非線性函數的條件，因而出現雙穩態的現象。這個論述仍須要進一步的檢驗。一般高對稱系統會具傋高簡併態，所以Lead salt nanocrystals可能出現非線性效應。PbSe有高簡併態 (ハ重簡併發生在L)， 球對稱之PbSe nanocrystal將此ハ重簡併分裂成雙重簡併及六重簡併。本工作經由keldysh Green function method探討流經單一量子點及耦合量子點(具傋高簡併態)之穿隧電流是否存在雙穩態現象。考慮PbSe nanocrystal, 因實驗可以量測PbSe nanocrystal 的穿隧電流，如此可以確認理論的可靠性。除此之外，我們也將計算流經分子的穿隧電流。此計算將考慮聲子效應。 ; This study attempts to investigate the tunneling current through individual quantum dots with highly degenerated states. We want to examine “ Is it possible to observe the bistable phenomena on tunneling process of nanostructures ?”. Such a bistable tunneling process has a crucial application in memory devices. Memory behavior of tunneling current was demonstrated in a double barrier system, a SiO2 junction and an inorganic junction. The mechanism of bistable current arises from electron-electron interactions. Nevertheless, such a behavior has not been experimentally reported in a single electron transistor. Some controversies still exist in theoretical works on if SETs provide a bistable tunneling current. For example, some works reported that bistable current only occurs in the SETs with negative electron-electron Coulomb interactions. Perhaps, tunneling current through a quantum dot maybe exhibit bistable behavior due to nonlinear behavior of occupation numbers arising from strongly electron correlation in the multi-fold degenerated states. Bulk PbSe material has an eight-fold degenerated state in L point, which is splited into the two-fold and six-fold degenerated states on spherical nanocrystals. We would like to theoretically study the tunneling current through a single quantum dot and coupled quantum dots having six-fold degenerated states in the framework of Keldysh-Green function technique. Considering PbSe nanocrystals, because experiments can measure the tunneling current through PbSe nanocrystals to examine the reliability of theoretical work. Besides, we will also calculate the tunneling current through the six fold degenerated state of molecular by considering electron-boson field interactions. ; 研究期間 9708 ~ 9807
