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Hydrogenated amorphous silicon-carbon alloy (a-SixC1-x: H) films are prepared by simultaneous if reactive sputtering of silicon and graphite in a H2–Ar gas mixture. The optical gap E 0 of a-Si x C1-x : H depends on alloy composition x and preparation conditions. The optical gap E 0 of a-Si x C1-x : H prepared under a same condition is ∼1.7 eV at x=1.0 (a-Si: H), increases with the decrease in x, reaches a maximum value of 2.2 eV at x=0.6 and then decreases with decrease in x, reaching ∼1.4 eV at x=0 (a-C: H). For films prepared at lower substrate temperature, the optical gap becomes larger. This behavior of the optical gap is discussed referring to the results of X-ray photoemission spectroscopy, infrared absorption measurements, etc., on a-Si x C1-x : H.

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A narrow-band emission has been detected at room temperature during the pulsed on state of a well-characterized threshold switching material, amorphous Te39As36Si17Ge7P1. The luminescence peak is centered around 0.55±0.03 eV, very close to half of the optical band gap of this material, 1.1 eV. This ratio of luminescence peak to optical band gap is similar to that obtained from the photoluminescence of a large class of chalcogenide glasses in their off states, strongly suggesting that the origins of the on-state electroluminescence and off-state photoluminescence are the same. The electroluminescence exhibits a threshold behavior, appearing only for on-state currents in excess of 4 mA. The output follows a Lambertian law for solid angles up to about 0.7 sr, and slowly deviates below the Lambertian law at larger solid angles. The width of the luminescence line is less than 0.1 eV, indicating that its origin cannot be blackbody radiation. This provides another confirmation of the electronic nature of threshold switching.

Reactively sputtered hydrogenated amorphous silicon film is used as the photoconductive target of a vidicon type image pickup tube. It is indicated that hydrogen partial pressure in the discharge gas has to be 40% or more in order to attain suitable image pickup tube characteristics. Photo-electric properties and lag-characteristics are enormously improved by lightly doping boron into amorphous silicon film, and a blocking type target structure is effective for suppressing dark current of the pickup tube. Using doped amorphous silicon film with a color-filter-integrated face plate, a single-tube color imager is fabricated.