ELECTRONIC TRANSPORT-PROPERTIES OF NITROGEN-DOPED AMORPHOUS-CARBON FILMS DEPOSITED BY THE FILTERED CATHODIC VACUUM ARE TECHNIQUE

Highly tetrahedral amorphous carbon thin films were deposited by the f iltered cathodic vacuum are technique at room temperature. Nitrogen wa s found to be a good n-type dopant of the tetrahedral amorphous carbon thin films. The Fermi lever shifts from 0.91 eV above the valence ban d to 0.65 eV below the conduction band with increasing nitrogen flow r ate from null to 16 seem (nitrogen partial pressure from 0 to 2.4 x 10 (-4) Torr). At the same time, the optical band gap drops from 2.7 to 1 .8 eV. Three electronic transport mechanisms, namely, transport in ext ended states, in band tails by hopping and variable range hopping (VRH ) near the Fermi level, were observed from the thermal activation meas urements in the temperature range from 100 to 450 K. The VRH transport parameters for ta-C films are studied. and the density of states near the Fermi level extracted from the hopping transport parameters was f ound in the range of 6.5 x 10(17)-9.7 x 10(19) cm(-3) eV(-1). The domi nant doping configuration is the substitution in the sp(3) coordinatio n at low N concentration and adoption of sp(2) bonding at high N conce ntration.