Phenomenological Considerations on the Photoconduction of Plasma-Polymerized Styrene Films in the Near-Ultraviolet Region

The photoconduction of plasma-polymerized styrene films was studied in the near ultraviolet region. The spectral response was independent of the polarity of the applied voltage and showed two photocurrent peaks at wavelengths of about 300 nm and 375 nm. These photocurrent peaks were nearly proportional to the 1.5 power of the applied electric field and the 0.85-0.86 power of the light intensity and inversely proportional to the film thickness, provided that the thickness exceeded the absorption depth. The response to step illumination exhibited a small but definite decay at a rate which increased with increasing film thickness. These characteristics are consistently explained by the existence of a partially photoconductive region near the illuminated surface.