GROWTH AND ELECTRICAL-PROPERTIES OF HIGH-PURITY ORGANIC MOLECULAR-CRYSTALS

Among organic crystals the class of aromatic crystals, built up of molecules which contain benzene ring sub-units, has found by far the greatest attention over the past two or three decades. But it has only recently been possible to achieve such low (sub-ppm) impurity levels in conjunction with high structural perfection for a few representatives that the intrinsic electrical transport properties could be measured down to near liquid He temperatures. High charge carrier mobilities, approaching those of silicon at room temperature, and pronounced nonlinear (subohmic) conductivities were discovered. An overview will be given on those crystal growth methods which are most suitable — while maintaining the high purity of ultrapurified starting material — to yield highly perfect single crystals (Bridgman, sublimation, and Czochralski growth). With respect to potential future applications of organic crystals in electronics and optoelectronies it appears necessary, however, to approach smaller geometrical dimensions in epitaxial layers and microstructures. © 1990, Elsevier Science Publishers B.V.. All rights reserved.