Electrical transport within polymeric amorphous carbon thin films and the effects of ion implantation

Here, we will discuss the electrical transport processes that occur within thin films of polymeric amorphous carbon, which possess a high resistivity of 10(15) Omega cm, a Tauc band gap of 2.6 eV, and a low defect density of 10(17) spins cm(-3). Using current versus voltage measurements, we have shown that the current is space-charge-limited, with a mobility value of typically 10(-10) cm(2) V-1 s(-1). The implantation of boron ions at doses below 6x10(14) cm(-2) results in an increase in mobility of more than one order of magnitude. Above this dose, the conductivity increases by five orders of magnitude, and the transport mechanism changes to a Frenkel-Poole type conduction process. At an intermediate dose of 2x10(15) ions cm(-2), the current versus voltage characteristic exhibits strong hysteresis. The observed hysteresis effects could be removed from one polarity by implanting only through the first half of the film. The hysteresis is likely to be due to the trapping of holes at one or both of the interfaces, resulting in the modification of the space-charge within the polymeric amorphous carbon film. (C) 2003 American Institute of Physics.