Dielectric interface modification by UV irradiation: a novel method to control OFET charge carrier transport properties

Abstract

The charge carrier transport in organic field effect transistors (OFETs) is determined by the transport properties of the insulator / organic semiconductor interface. We demonstrate that an adequate treatment of this interface results in a polarity change of the OFET charge carrier transport properties, without further altering the device structure. Illuminating the utilized PMMA polymer dielectric, by using UV radiation, leads to the introduction of mainly electron traps at the dielectric interface. This results in the suppression of the electron transport for an otherwise n-type pentacene OFET. However, as a consequence of trapped electrons in the near surface layer of the PMMA dielectric, the hole transport of the device is enabled though a hole blocking source/drain metallization. This effect, as well as the impact of the UV irradiation on the PMMA dielectric will be discussed in detail. The UV treatment yields a PMMA interface rich on polar groups. The influence of these groups on the OFET characteristics is investigated by studying several polymer dielectrics with varying content of the emerging groups.