Molecular semiconductors: Terahertz spectroscopy of charge transport on the nanoscale

• Applicant: Professor Dr. Roland Kersting
• Subject Area: Experimental Condensed Matter Physics
• Term: from 2019 to 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 420459768

Over the past two decades, the development of organic field-effect transistors (OFETs) brought first applications into reach. The mobilities obtained on thin-film OFETs, however, converged at values of about 10 cm2/Vs, which may not be sufficient for many applications. Additionally, the fundamental understanding of carrier transport has not reached the level known from inorganic semiconductors. With the proposed research, we want to shed light on two processes that are expected to slow down transport in molecular semiconductors. These are the carrier-phonon interaction that leads to polarons and the dynamic localization of charges.The proposed work is stimulated by the insight that both, polarons and dynamic localization may be efficiently screened within the channel of OFETs, which should lead to free carriers and Bloch-like transport. In order to access these fundamental properties of carrier transport, we will perform terahertz (THz) transmission experiments that probe the local transport on the nanoscale and are not affected by grain boundaries or other extrinsic parameters. From the THz data, effective masses of the carriers, as well as their scattering times, will be obtained. Their temperature dependencies will show how polaron formation and dynamic localization affect transport. Of particular interest is the extent to which these processes are screened by charge carriers at densities, which are typical for the inversion layer of OFETs. The expected results are not only of fundamental interest, but they also may stimulate the development of novel molecular semiconductors and may lead to a significant leap in mobilities that brings OFETs closer to application.

• DFG Programme: Research Grants