有機半導體與無機半導體中雜質態的研究與影響

Abstract

在這個論文中，我們研究兩個與半導體中與雜質有關的物理課題．第一個部分我們利用共振態的觀念，在無機半導體中，產生兆赫波段頻率的光源．藉由數值解出動量空間中的波茲曼動力方程式，我們證明在一般可行的情況下，載子的分佈反轉是可以達到的，也在理論上證明了這個固態系統發出兆赫雷射的可能．第二各部分，我們有興趣有機半導體中，具有對氧氣敏感的電性．具體上有兩個問題，第一個是載子的傳導率在有機半導體中通常可以看到有好幾個數量級以上的差距，且電動通常比電子要來得快，這與無機半導體的情況有很大的差異．我們利用氧氣的吸附，以及有機半導體中常見的缺陷，來解釋這樣的實驗現象．我們發現到，原本缺陷對於電子與電洞有相同的束縛能力，可是在氧氣吸附在缺陷之後，對電子的吸附能力增強了，而對電洞卻沒有改變．另一個我們有興趣的課題是氧氣參雜的效應，這會使得有機半導體的場效電晶體，無法有效的關閉．除此之外，物理上這各參雜效應無法藉由氧氣的電子親合能來解釋，我們利用一各自洽的能帶計算，來闡明這各參雜與有機半導體離子化能之間的關係，以及照光是否影響這各參雜效應．

This dissertation is divided into two parts which both relate to the impurity in semiconductors. The first part deals with a solid state system which is able to generate THz radiation by the concept of resonant state. Such state is a hybrid state of a localized impurity state and a continuum. By numerically solving the Boltzmann kinetic equation, we are able to show that a population inversion is possible in a practical condition. The second part deals with the sensitive electronic properties of organic semiconductors to the presence of adsorbed oxygen molecules. There are mainly two questions in this part. One is the huge mobility imbalance among electron and hole carriers. We found that once an oxygen molecule adsorbed onto a defect site, the binding energies for trapped electron will increase while that for trapped hole remains. The asymmetric binding energies are the essence of such mobility imbalance. The other interesting effect by oxygen molecule is the p-doping which cause a undesired off-current in polymer field-effect transistors. Such doping is not able to reconcile with the low electron affinity of oxygen molecules. By calculating the band structure of an oxygenated polythiophene, we are able to clarify the dependence of doping on the ionization potential of host material and the conditional illumination.