Conductivity and photoconductivity of granular silver films on a sapphire substrate

The photoelectric properties of a high-resistance silver film on sapphire, consisting of granules 15–20 nm across with the same intervals between them, have been investigated. The ohmic conductivity of the film increased with temperature. Photoconductivity is detected in the film when optical radiation with wavelengths up to the red limit of the photoelectric effect acts on it. A sign change of the photocurrent is detected in the photoconductivity spectrum when the current through the film increases under the action of radiation with wavelength less than 460 nm, whereas it decreases when the wavelength is greater than 460 nm. A conductivity and photoconductivity model is proposed that is based on doping of the dielectric substrate due to the metallic nanoparticles placed on it and the motion of electrons over traps in the substrate. The position of the bottom of the conduction band of the dielectric relative to the Fermi level for silver is calculated in terms of the model.