An audio-frequency (af) (10-100 kHz) glow discharge has been used for plasma chemical vapor deposition of thin films from organic compounds of the carbon family. It has been realized employing a recently designed reactor, equipped with three electrodes-a small electrode on which films are deposited, and two main electrodes sustaining a glow discharge. The small electrode and one main electrode are connected by a variable capacitance C. It has been found that small changes of C can cause a drastic change in the electronic properties of deposited films. This effect, attributed to a transition between the amorphous insulator (a-I) and amorphous semiconductor (a-S), is discussed for hydrogenated carbon-silicon, carbon-germanium, carbon-tin, and carbon-lead films produced from adequate organometallic compounds. To better understand the deposition process in the reactor, the electrical characteristics of model argon plasma have been investigated by means of a Langmuir single probe movable in the space between the reactor electrodes. Both af potentials of the plasma and typical current-voltage characteristics have been measured. It has been found that energetic conditions of the plasma, and consequently, the plasma chemistry, are independent of C. Changes of C have, however, influence on the ion bombardment process taking place in the vicinity of the small electrode. The ion impact energy E-max has been roughly estimated and a relation E(max)proportional to ln C is found. The calculated values of E-max, which change from almost zero to several tens of-electron volts, are in a good agreement with results of an experiment performed in the reactor with argon sputter etching of a gold film.