Exploration of Ultrafast Carrier Dynamics In Polymer Semiconductors Using Terahertz Spectroscopy

University Of California-Santa Barbara, Santa Barbara CA

Investigators

Abstract

0070285 Moses The carrier dynamics in conjugated polymers in the sub-picosecond time scale are generally unknown. Recent developments in terahertz (THz) spectroscopy have opened a new window to the carrier transport in this time regime. This technique has so far been applied mostly to "conventional" semiconductors. In this project advantage will be taken of this powerful experimental probe in using it to study the carrier dynamics in various conjugated polymers. The goals of this exploratory research are focused on a selected few currently open questions. Three studies will be undertaken. Firstly, the charge transport promptly following photoexcitations will be studied while the carriers occupy extended states, and before significant carrier trapping and recombination can occur. Secondly, a study will be performed on how the strength of the inter-chain coupling modifies the carrier transport by exploring the transport in PPV and its various derivatives, and thirdly, the soliton dynamics in polyacetylene at high bias fields will be studied. In this case the soliton velocity is predicted theoretically to reach a plateau, a prediction that has yet not been verified. The transport measurement is based on the fundamental process of electromagnetic radiation, typically in the THz range, emitted by the induced transient photocurrent. Monitoring the time-evolution of the THz signal provides information regarding the transient photoconductivity in the 0.1 to 10 ps time scale. This research employs state-of-the-art experimental techniques. Graduate students and post doctoral research associates will participate in this research and thereby acquire up-to-date- knowledge and skills in a forefront area of contemporary condensed matter physics and materials science. %%% Following the discovery of semiconductor polymers as promising materials for light emitting diodes (LEDs) and lasers, an active research effort has emerged worldwide in pursuit of the goal of realizing "plastic" lasers, LEDs, and fast photo-detector devices based on conjugated polymers. This project is concerned with the investigation of several unsolved questions concerning the nature of the light emission process in quasi-one dimensional polymer semiconductors promptly following photoexcitation. These processes occur at ultrafast time scales and their studies are now made possible by new developments in experimental ultrafast spectroscopy. This project is concerned with using these new techniques in the quantitative study of the nature of the processes that underlie the ultrafast emission of light following photoexcitation of various polymer materials. This research will be conducted with the assistance of students and post doctoral research associates who will thereby acquire skills and knowledge in a contemporary forefront area of condensed matter physics and materials science. ***