INFRARED PHOTORESPONSE OF CARBON-FILMS PREPARED BY PLASMA DECOMPOSITION OF PROPYLENE

The photoconductive effect of carbon films prepared by plasma decomposition of propylene was investigated for infrared radiation between 520 and 4200 cm-1. The carbon films deposited on glass substrates and on n-type silicon substrates showed an increase in electric current, i.e., photocurrent, on infrared irradiation. The increase in current by irradiation depended on the wave numbers of the light: the current was greater for lower wave numbers, and this spectral response suggested that the increase in the current was caused by an absorption of photons and not by the thermal effect of radiation. The dark current-applied voltage characteristics of the junctions between carbon films and n-Si varied with their preparation temperature (T(p)) from rectifying behavior through backward diode behavior to ohmic behavior. The increments in current upon the infrared radiation of all films strongly depended on the applied voltage. The constituent that contributes to the photocarrier generation was estimated to be the poorly stacked condensed aromatic portions in the carbon films, using an infrared absorption parameter proposed by us, which represents the density of states of the pi-electrons in carbons.