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CPP: Chemische Physik und Polymerphysik

CPP 21: SYMPOSIUM Functional Organic Thin Films II

CPP 21.4: Vortrag

Donnerstag, 30. März 2006, 15:00–15:15, ZEU Lich

Field Effect Transistors and Space Charge Limited Currents on Perylene Single Crystals — •G. Ulbricht¹, J. Smet¹, A. Tripathi², J. Pflaum², and K. von Klitzing¹ — ¹Max Planck Institute for Solid State Research, 70569 Stuttgart — ²Universität Stuttgart, 3. Physikalisches Institut, 70550 Stuttgart

To understand the fundamental charge carrier transport in organic semiconductors, research on single crystals is necessary. Perylene is a well studied organic semiconductor and known to show high mobilities in time of flight experiments at low temperatures. We are studying Perylene single crystals by measuring space charge limited currents (SCLC) and field effect transistors (FETs). In the SCLC sandwich geometry, the crystals show exceptionally low trap densities down to 3·10¹² cm⁻³ as well as a distinct hysteretic behaviour. The latter helps to interpret the SCLC data significantly, in particular while contacts are not ideal. FETs were fabricated on the surface of Perylene crystals and characterised down to 180 K. Only hole conduction was observed. With as-prepared contacts, we calculated from the FET characteristics a lower limit of the mobility of about 10⁻⁵ cm²/Vs. Clear signs for the existence of significant contact barriers motivated us to explore different electrode materials and fabrication methods. We show that contact barriers can be significantly reduced by annealing source and drain electrodes after deposition. This does not change the threshold field of about 7·10⁷ V/m, but raises the lower limit of the hole mobility measured by 2-point FET characteristics up to 1.3·10⁻³ cm²/Vs. Supported by the DFG (Sm64/4, Pf385/2)