Electron and Hole Mobilities in High Purity Anthracene Single Crystals

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Abstract
Using ultrapurified, highly perfect anthracene crystals electron and hole mobility data were measured by the time-of-flight method over a wide temperature range along 5 different crystallographic directions. From these results full tensor data (principal axes mobilities, tensor orientations and tensor rotations with temperature) have been determined. The highest principal electron mobility component is close to the a axis, reaching 35cm2/Vs at 20K, the highest hole component along b, reaching 50cm2/Vs at 35K. For electrons moving along the crystallographic c direction a transition from a nearly temperature-independent mobility (400K-100K) to a mobility increasing upon further cooling has been found, with very similar absolute values and transition temperature as previously reported for naphthalene and explained as a hopping to band transition. A non-Ohmic, sublinear velocity–electric field relation, reflecting hot charge carriers, has been obtained between 20 and 36K for electrons drifting along a, with a tendency of velocity saturation between 0.5 and 1·106cm/s, similar to what has been reported before for naphthalene and perylene. Different samples set different low temperature limits to a determination of microscopic time-of-flight mobilities by an onset of trapping, probably at structural defects, induced during handling and measurement.