Vanishing space-charge effects in contact-limited thin-film diodes

Estimation of charge-carrier mobility and trap energy from a space-charge-limited-current measurement is a well-established technique for the characterization of electronic materials. However, classical solid-state theories referenced for parameter extraction are based on simplistic assumptions that may not be strictly valid for a new generation of devices from unconventional materials and processing. In this study, we show that contact-limited currents dominate the entire operating regime in thin-film or nanoscale diodes even at a small charge-injection barrier. This assessment can make many reported values and analysis routines debatable, because they do not generally take any contact effects into consideration. Physical origins of the validity problem and guidelines for holistic parameterization are detailed through systematic correlation of analytical models, numerical simulation, and an experimental investigation into an organic diode with a graphene contact.