Tetrahedral amorphous carbon film (ta-C, rich in sp(3) bonds), 50 nm thick,
was deposited by magnetron sputtering on n-type Si substrate at room tempe
rature. Ohmic contact to the ta-C film was formed by depositing stoichiomet
ric titanium nitride (TiN) by magnetron sputtering or aluminum (Al) by elec
tron-gun evaporation at room temperature. The capacitance-voltage character
istics at different temperatures show negligible hysteresis, indicating low
concentration of mobile charges. Electrical conduction in the TiN (Al)/ta-
C/n-Si structure, with the TiN or Al biased positively with respect to Si.
was investigated in the temperature range 80-300 K. Under high-field condit
ions, the electrical conduction is consistent with thermally assisted Fowle
r-Nordheim tunnelling of electrons from the Si substrate into the ta-C film
for temperatures for 80-260 K and trap-assisted band-to-band indirect tunn
elling for higher temperatures. Under low-field conditions, Poole-Frenkel e
mission dominates over tunnelling for temperatures even well below room tem
perature. The temperature dependence of the tunnelling current was explaine
d in terms of the change in the effective barrier height at the ta-C/n-Si i
nterface.