STEADY-STATE AND TRANSIENT CURRENT TRANSPORT IN UNDOPED POLYCRYSTALLINE DIAMOND FILMS

We have investigated steady-state and transient electrical properties of undoped polycrystalline diamond thin films deposited using hot fila ment chemical vapor deposition on (100)-oriented n-type and p-type sil icon substrates. The capacitance-voltage characteristics are strongly influenced by slow traps located close to the interface between the di amond layer and the silicon substrate. When interpreting data one has to consider that the traps are not in thermal equilibrium-during measu rements. The steady-state current through the diamond him has the same behavior for films deposited on both n-Si and p-Si. Its temperature a nd held dependency can be interpreted in terms of Poole-Frenkel transp ort involving ionized sites with overlapping potentials in the diamond film. Electrically excited current transients decay with time accordi ng to a power law. The kinetics depend only weakly on temperature. Fur ther, the transients contain very long time scales and show much simil arity to earlier reported optically excited ones. The temperature and voltage dependency of the transient current magnitude are similar to t he ones of the steady-state current for a nonzero field across the dia mond layer during the transient. It is possible to qualitatively accou nt for the steady-state and transient transport within the framework o f the same basic model assuming that the traps involved in the transpo rt have a certain spatial and energy distribution. From an application point of view the leakage currents in the diamond film are of accepta ble 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 reli ability; from the electrical measurements no sign of degradation of th e diamond films due to long term current stress can be seen. (C) 1997 American Institute of Physics.