ELECTRONIC DENSITY-OF-STATES IN HIGHLY TETRAHEDRAL AMORPHOUS-CARBON

Highly tetrahedral amorphous carbon (ta-C) films and its hydrogenated form (ta-C:H) have been deposited using a filtered cathodic are. In this paper, the optical and electronic band-gaps of amorphous diamond and its hydrogenated form ta-C:H, are shown to be in the range 2 eV. The H content of ta-C: H is found to be about 3 at.% using elastic recoil detection analysis (ERDA) and electron energy loss spectroscopy (EELS) is used to show that ta-C:H does keep its tetrahedral structure. Both materials are found to be stable at temperatures up to 1000K. The room temperature conductivity of 10(-7)10(-8)Omega(-1)cm(-1) is shown to be thermally activated, with activation energies in the range 0.2-0.3 eV. A detailed study made from the current-voltage characteristics of ta-Clp-Si heterojunctions shows that current flow is space-charge limited (SCLC) and influenced by bulk traps. The density of states profile, N(E), in the region of the quasi-Fermi level is calculated using the differential method and found to be of the order 10(18) cm(-3) eV(-1). Optical absorption data is coupled with the electrical results to confirm that the valence band density of states is of the order 10(21) cm(-3) eV(-1). It is also shown that there is a reduction of nearly one order of magnitude in the N(E) at the quasi-Fermi level upon hydrogenation. SCLC measurements are complemented with surface admittance measurements (SAM) which yield a value of 10(11) cm(-2) eV(-1) for the interfacial density of states at the ta-C/p-Si junction. A decrease in N-ss is also observed at the ta-C:H/p-Si interface in agreement with the SCLC results.