Cyclotron resonance and carrier scattering processes in anthracene crystals

Abstract

Cyclotron resonance experiments on holes orbiting in the ab plane of an anthracene crystal are described in detail. We were unable to reduce the cyclotron resonance experiment to a routine procedure and consequently are able to report useful cyclotron resonance measurements on only a few (six) anthracene crystals. Nevertheless we have been able to obtain useful information on the valence band structure and hole scattering properties in anthracene from these measurements. The measured effective mass of 11 me, where me is the free electron mass, is shown to be in qualitative agreement with calculations of the effective mass tensor. From the shape of the cyclotron resonance line at 2 K, we have obtained experimental hole scattering times ranging from 4×10−10 sec down to 10−12 sec and below depending on sample quality. By a detailed examination of the possible low temperature scattering mechanisms, we have concluded that, at 2 K, holes in anthracene are most efficiently scattered by charges trapped at point defects, either chemical impurities or local lattice defects.