Quantum size effects in amorphous diamond-like carbon superlattices

Evidence for the existence of quantum size effects in amorphous diamond-like carbon superlattice structures from optical and electronic measurements together with theoretical predictions are reported. A `blue shift' in the optical gap is shown to occur with decreasing well width from which an effective mass for the electrons (and holes) is obtained. Regions of negative differential resistance are observed in the current-voltage characteristics at temperatures ranging from 4–300 K. Dark conductivity studies point to a current that is dominated by a tunnelling component rather than thermal carrier emission over the barrier layers of the superlattice. Activation energy studies show an increase in the activation energy with decreasing well width, in keeping with the observed optical `blue shift'. The voltage range over which negative differential resistance is measured agrees well with resonant tunnelling predictions.