Steady-state and transient current transport in undoped polycrystalline diamond films

Abstract

We have investigated steady-state and transient electrical properties of undoped polycrystalline diamond thin films deposited using hot filament chemical vapor deposition on (100)-oriented n-type and p-type silicon substrates. The capacitance-voltage characteristics are strongly influenced by slow traps located close to the interface between the diamond layer and the silicon substrate. When interpreting data one has to consider that the traps are not in thermal equilibrium during measurements. The steady-state current through the diamond film has the same behavior for films deposited on both n-Si and p-Si. Its temperature and field dependency can be interpreted in terms of Poole–Frenkel transport involving ionized sites with overlapping potentials in the diamond film. Electrically excited current transients decay with time according to a power law. The kinetics depend only weakly on temperature. Further, the transients contain very long time scales and show much similarity to earlier reported optically excited ones. The temperature and voltage dependency of the transient current magnitude are similar to the ones of the steady-state current for a nonzero field across the diamond layer during the transient. It is possible to qualitatively account for the steady-state and transient transport within the framework of the same basic model assuming that the traps involved in the transport have a certain spatial and energy distribution. From an application point of view the leakage currents in the diamond film are of acceptable magnitude for many diamond based silicon-on-insulator applications intended for operation at moderate temperatures and voltages. Finally, the films also show promising behavior with respect to material reliability; from the electrical measurements no sign of degradation of the diamond films due to long term current stress can be seen.