Zener Tunneling In Organic Semiconductors

Zener firstly predicted the electron interbands transition in periodic potential field. This transition was called Zener tunneling. Zener tunneling was widely applied in the semiconductor science, superconducting science, photo-electron science and electronics. Based on the principle of Zener tunneling, people developed new electronic devices Zener Diodes, Josephson Junctions, and accelerated atoms in photo crystals. As a charming and useful physics phenomenon, Zener tunneling attracted people to study it for long.But it seems that, people focused on Zener tunneling in inorganic semiconductors more than that in organic semiconductors. Few people tried to give a clear picture of Zener tunneling in organic materials. In one dimensional conjugated polymer, people believe that the gap originated from Peierls instability. Different from inorganic semiconductors, there is a strong electron-lattice interaction in organic semiconductors, which makes its energy bands evolution caused by external liner electric field very complicated. At this case, what is the picture of Zener tunneling in organic semiconductor? What is the difference between it in organic and inorganic semiconductors? Stimulated by these questions, we had the most common material polyacetylene as the object, to calculate its electron states evolution caused by the uniform electric field. We finally got a clear picture of Zener tunneling in organic semiconductors, and compared it with the case in inorganic semiconductors.In chapter one, we systematically introduced the research about Zener tunneling. It involved many experiments and applications in the past decades. The theoretical researches were also introduced here, which contained semi-classical method and quantum perturbation method. We hope to use these methods to research Zener tunneling in organic semiconductors in the future. We have a deeper knowledge that, besides the tunneling of band electrons, any periodic systems, such as photo crystal, phonon system, spin system which has a Haldane gap, if they were exposed in a liner external field, the band quasi particles may transit through the gap into another band. We call these phenomenon Zener tunneling. So we can study Zener tunneling in some new systems and the concept of Zener tunneling is broadened.In chapter two, we began to introduce some knowledge of Zener tunneling in organic semiconductors, and we found the related researches are very few. Kazumi Maki firstly proposed a model that the creation of soliton pairs caused by electric field played an important role in the transport properties of Charge-Density-Wave Condensates at low temperatures. A.B.Kaiser systematically researched the conducting properties of conjugated polymers at low temperatures. All their achievement gave me beneficial inspiration. We could easily predict that, the electron-lattice coupling plays a crucial part in Zener tunneling in organic semiconductors. We guess that accompanied by Zener tunneling, we can observe located electron states. We also introduced studies about Zener tunneling in the Single Wall Carbon Nanotubes (SWNT) and Grapheme NanoRibbons (GNR). At last of this chapter, we introduced the latest research about Bloch oscillation and Zener tunneling in one dimensional organic lattice.In chapter three, we adopted the SSH model to deal with the electron system of polyacetylene, and got the electron-lattice equation under strong electric field. We calculated the results self consistent. Under a certain external electric field, we compared the energy of different occupied states, and the one has the lowest energy is the stable state. Through this way, we can judge whether Zener tunneling occurs or not. While Zener tunneling occurred, we calculated its band structure, electron density and the lattice configuration. When the strength of electric field reaches a critical point, charge polarization and lattice distortion can be observed suddenly. We also calculated the Zener tunneling in rigid lattice, and compared the two Zener tunnelings. The local state in organic semiconductors could support Zener tunneling. Go on strengthening the electric field, more electrons tunneled. The effect of electron-lattice coupling constant is also calculated. We did not take the electron-electron coupling into count, so we did not know the effect of the collection of space charges on the two ends of chains. Our model could not deal with the case that fraction number of electron tunneling either. All these defects need us to improve our model again and again.