Space-charge-limited-trap-limited-currents in anthracene crystals

Abstract

Space-charge-limited-trap-limited hole currents in anthracene crystals are interpreted in terms of a trap distribution which starts at a discrete trap level at 0·6–0·8 eV and in which the trap density falls off exponentially with energy relative to this level. It is suggested that exponential hole trap distributions are produced by physical perturbations of the crystal lattice introduced by the same impurities which give rise to the discrete hole trap level at 0·6–0·8 eV (revealed by thermally stimulated current studies). The results indicate that a perturbed molecule is introduced for every 10,000 impurity molecules and the total number of perturbed molecules is constant at 10 17 m −3 for melt-grown and vapor-grown crystals. The parameter kT c varies from crystal to crystal, indicating that the relative contributions of highly perturbed and slightly perturbed molecules is influenced by crystal growth conditions.