Low temperature conductivity in plasma deposited amorphous dielectric films

Investigations on electrical properties of amorphous dielectric films have revealed, in some cases, a measurable conductivity at low temperatures (down to 77 K). This effect was attributed to variable range hopping between states lying near the Fermi level and was described by Mott´s law. Subsequent studies, however, carried out over much broader temperature ranges, have shown that Mott´s law is not satisfied and the conductivity at a given electric field becomes completely temperature independent below a critical temperature. This phenomenon is studied based on measured DC conductivity at low temperatures and voltage-pulse-induced time-domain depolarization (VPITDD) experiments. Samples of films deposited by plasma decomposition of hexamethyldisilazane, hexamethyldisiloxane, and tetramethylsilane were investigated. Although the results obtained seem to confirm the existence of a second transport channel in some amorphous dielectric films, the nature of states responsible for this mechanism is not yet known