ELECTRICAL AND OPTICAL-PROPERTIES OF PLASMA-DEPOSITED AMORPHOUS HYDROCARBON FILMS

Amorphous hydrocarbon layers (a-C:H) prepared by plasma assisted chemical vapor deposition (PECVD) were investigated with respect to their possible semiconducting properties. Cluster calculations were performed to confirm that a true band gap may be formed in these materials. Values corresponding to those derived from optical investigations were calculated. Electrical conductivity is in accordance with a variable range hopping mechanism over a large temperature range. Conductivity and gap width vary with the preparation conditions, but for the same bandgap, the conductivities of the nitrogen containing films were always lower than that of the pure hydrocarbon films. From this we conclude that doping resulting in a shift of the fermi level does not occur in the case of nitrogen.