COMPARISON OF PURITY AND PERFECTION OF VAPOR- AND MELT-GROWN ANTHRACENE CRYSTALS

The purity and perfection of anthracene crystals have been examined for melt-grown and thick (>1 mm) vapor-grown crystals. The physical properties studied were the charge carrier lifetime and mobility of holes, dislocation density, and the bulk self-diffusion coefficient. Chemical purity was assessed by gas chromatography. Melt-grown crystals had hole lifetimes >1 msec compared with 220 μsec for the best vapor-grown crystal, although vapor-grown crystals had lower dislocation densities and fewersubboundaries. Vapor-grown crystals had lower measurable impurity concentrations, ∼2 ppm compared with ∼10 ppm for melt-grown crystals, but these impurities appear to have no effect on charge carrier trapping. Both types of crystals gave the same self-diffusion coefficient at 190°.