Metal contacts and electrical processes in amorphous diamond-like carbon films

Amorphous diamond-like carbon (a:DLC) films, of high hardness (4700-5200 kg mm(-2)) and an optical bandgap of 1.0-1.1 eV, were deposited by employing a rf plasma sputtering system in a methane environment. Rectifying metal-insulator-metal (MIM) devices, based on a:DLC as the insulator film, with Al deposited as the bottom contact and Al, Cu or Au as the upper contact, were prepared. Electrical measurements of the MIM devices where the bottom contact was Al and the upper contact was Al, Cu or Au have shown that there is a barrier between the a:DLC film and the Al upper contact which was not detected in MIM devices with Cu or Au as the upper metal contact. The dependence of the conductivity sigma on frequency f at low (f<1 kHz) and high (f>1 kHz) values corresponded to the conductivity of the interface and the bulk respectively. The dependence of sigma on frequency at high frequencies (bulk charges) showed a frequency function of the type sigma similar to f(s), where st 1, and is also frequency dependent. Some of the injected carriers are lost in traps (e.g. in trap level of 0.34 eV) on the localized states within the bandgap during the conductivity process in a:DLC films. Including the carriers lost to the process enabled us to explain the frequency dependency of s.