Amorphous semiconductors have potential usefulness in optical memory and imaging applications.
Phenomena of amorphous-crystalline transformation, changes of optical properties, transmission and refractive index, in the amorphous phase, photo-doping, and photodecomposition are discussed in somewhat detail, after a brief description of sample preparation technique.
Direct dot writing and erasing with laser radiation are carried out with pulsed light of μ sec duration. This reveals existence of photo-enhanced crystallization besides usual thermal crystallization.
Absorption edge shift upon illumination and heating at temperatures below the glass transition temperature, observed in (Se, S)-based amorphous materials, is not related with crystallization.
Doping of metals into chalcogenide films by illumination (photo-doping) provides means of changing physical properties of the film.
Examples of optical memory and high-resolution imaging using amorphous-crystalline transformation are given. Holographic recording of bit patterns and supermicrofiche are produced in the (Se, S)-based chalcogenide films. Their recording characteristics are described.

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Mechanism of photoconductot formation from chemical precipitate CdS is investigated. Six different chemical precipitates are used for starting materials. Hexagonality, reflectivity and spectral sensitivity are measured to know the property of the precipitates. The precipitates are fired after additions of an activator in the form of CuCl₂ and an CdCl₂ flux.
The results of differential thermal analysis, thermogravimetric analysis, and of measurements of particle diameter, spectral sensitivity and absorption due to Cu ions show the property of the photoconductor obtained here is strongly dependent on the property of the precipitate. Particle diameter, peak height ratio and absorption due to Cu ions decrease as specific volume of the precipitate increases. Particle diameter, peak height ratio and absorption due to Cu ions are correlated each other.

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The authors have presented a new imaging system involving photo-electrolytic dyeimage formation on zinc oxide photoconductive layer. To prepare the imaging sensor, 4 (pdimethylamino styrylquinoline) was coated on or dispersed in the zinc oxide-resin layer which was supported by an aluminium sheet.
When the sensor was imagewisely exposed to UV light and voltage was anodically applied to it simultaneously, purple colored dye image was formed on the zinc oxide surface.
Since the produced dyes act as spectral sensitizer for photoconduction of zinc oxide, the zinc oxide layer with dye image is expected to work as an electrostatic duplicating master.

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The mechanism of formation of electrically conductive image by photolysis of silver alginate film is discussed from the results of the mesurement of electric resistance and the observation of the surface and cross section of irradiated silver alginate film. These show that silver atoms produced by irradiation aggregate to form the colloidal silver particles near the irradiated surface and finally form a thin silver layer which is electrically conductive.

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