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SYCT: Symposium Charge Transfer Effects in Molecular Materials

SYCT 1: Symposium Charge Transfer Effects in Molecular Materials

SYCT 1.5: Hauptvortrag

Montag, 11. März 2013, 11:30–12:00, H1

Electron transport in organic single-crystal transistors and Schottky-gated heterostructures — •Alberto Morpurgo — University of Geneva, Geneva, Switzerland

Organic single-crystal transistors have unprecedented quality and enable the investigation of several interesting phenomena (band-like transport in, the Hall effect, interfacial polarons, etc.). So far, virtually only p-type devices have been studied. Here, I will discuss electron transport in single-crystal FETs and heterostructures, showing how the best n-type devices perform at the level of their p-type counterparts. I will first focus on PDIF-CN2 single-crystal FETs, in which we observe the characteristic signatures of band-like transport (electron mobility increasing upon cooling and of Hall effect). The experimental results, and a comparison with p-type materials in which band-like transport in FETs is observed, suggest that the coupling of the charge carriers to the polarizability of the organic semiconductor plays a key role in determining which organic materials are more likely to exhibit band-like transport. Next, I will discuss new Schottky-gated heterostructures based on rubrene and PDIF-CN2 crystals, in which a conducting 2D layer forms spontaneously due to charge transfer. Gate-dependent transport and Hall measurements show that electrons are responsible for the conductivity, and that their density decreases linearly with decreasing temperature. We understand this behavior in terms of the heterostructure band-diagram, which quantitatively captures the slope of the linear temperature dependence. In the best devices, the electron mobility remains as high as ~ 1 cm2/Vs at T=30 K.