Physical Society Colloquium

Interesting properties of organic semiconductors, such as high carrier mobility, low trap density, and good air stability have attracted considerable attention, recently. For many possible applications, like organic lasers, organic light emitting diodes, or organic integrated circuits, the knowledge of intrinsic properties achievable in very pure and perfect crystals is important. Therefore, we have carried out a program to grow single crystals of unusual high purity and crystalline perfection. Using a gas phase transport method, we have produced millimeter - sized crystals of acenes, oligothiophenes, phtalocyanines oligophenylenevinylene, fullerene and many other organic semiconductors. Some of these compounds can have electrically active impurity concentrations of the order of 10¹³ cm^-3. Mobilities up to hundreds thousands cm²/Vs at low temperature can be achievable in some materials. Field-effect doping has been applied to study electronic properties of these crystals. In some cases, the charge density in the field-effect device channel has been increased into the range of one or more charge carriers per molecule. Thus insulators can be transformed into metals, and even superconductors. Superconductivity has been successfully induced in single crystals of arenes, (pentacene Tc=2K, tetracene Tc=2.7K, anthracene Tc=4K) oligophenylenevinylenes (trimer Tc=4.2K , tetramer Tc=2.9K and pentamer, Tc=2K) sexithiophene, polymer thin film (regioregular polythiophene, Tc=2.35K) and single crystals of pure and intercalated fullerenes (hole and electron doped C60 Tc=52 and 11K, C70, Tc=7K and substituted C60, Tc up to 117K).. Due to high charge mobilities in the high quality of organic semiconducting samples the integer and fractional quantum Hall effects has been observed. Moreover, an injection laser has been fabricated using field effect electrodes for efficient charge injection.

Friday, May 10th 2002, 15:30
Ernest Rutherford Physics Building, Keys Auditorium (room 112)