Amorphous semiconductor and amorphous insulator — two kinds of hydrogenated carbon–silicon films fabricated in the three-electrode reactor

Amorphous hydrogenated carbon–silicon (a-SiXCY:H) films were produced by plasma-enhanced chemical vapor deposition (PECVD) in an audio-frequency (a.f.) three-electrode reactor using tetramethylsilane as a source compound. The negative amplitude of a.f. voltage, V(−), measured on a small electrode, on which the films were deposited, with respect to the ground was the only operational parameter of the deposition process. Investigations on electrical conductivity, optical absorption and internal photoemission were carried out. It has been found that a rapid transformation in the electrical conductivity occurs when V(−) changes from 600 to 750 V (from 10−16 to approx. 10−8 S/m). This effect has been attributed to the amorphous insulator–amorphous semiconductor transition, which is controlled in this case by a percolation process.