Shirou Suzuki

Improvement photoelectric conversion efficiency of red light in HARP film

We enhanced the photoelectric conversion efficiency of red light in a 15-&mgr;m-thick HARP film without deteriorating image pick-up characteristics or reliability. To achieve a higher photoelectric conversion efficiency for red light, we designed a new film structure with an increased amount of doped Te, which has a narrower band gap than that of a-Se. The thickness of the LiF-doped layer for trapping holes was increased from that of the conventional red-extended HARP film in order to weaken the internal field that would otherwise be enhanced by trapped electrons in extra doped Te. The new red-extended HARP film achieved a photoelectric conversion efficiency for red light of about 22.5% at a wavelength of 620 nm, which is twice that of the conventional red-extended film. We confirmed an improvement in signal to shot noise ratio of 3 dB and a dramatic improvement in color reproduction when we experimented with an HDTV camera with a camera tube incorporating the new film.

Heat treatment to suppress image defect occurrence in amorphous selenium avalanche multiplication photoconductive film with improved red-light sensitivity

Amorphous selenium (a-Se) avalanche multiplication photoconductive film, HARP film, has been developed for the purpose of making a high sensitivity video camera. HARP film used for the red channel in a color camera is doped with tellurium (Te) to improve its red-light sensitivity. However, doping a-Se with Te causes impurity levels that trap electrons, and the built-in-field from the trapped electrons causes image defects when a camera using the film is shooting intense spotlights. A heat treatment to suppress the defect occurrence was found. We describe this treatment and discuss its mechanism.