Shiro Suzuki

Photoconductive properties of organic films based on porphine complex evaluated with image pickup tubes

We have fabricated two types of organic photoconductive films; a layered structure of tetra(4-methoxyphenyl) porphine cobalt complex (Co–TPP) and bathocuproine (BCP) (target A), and another of Co–TPP, tris-8-hydroxyquinoline aluminum (Alq3) and BCP (target B). The photoconductive properties of each film have been measured using image pickup tubes. The dark current was drastically reduced in target B compared with that in target A at the same applied electric field. The external quantum efficiency reached 20% in target B, which is twenty times higher than that in target A. Image pickup of a test chart from target B at standard TV operation was also demonstrated. High resolution and excellent tone sufficient for television use has been obtained.

Ultrahigh-sensitivity new super-HARP camera

NHK led the world in developing a high-sensitivity Super-HARP pickup tube using the avalanche multiplication effect. The authors have now developed an improved version (2/3- inch, with electromagnetic focusing and electromagnetic deflection) which is eight times more sensitive and has much better lag characteristics. The handy New Super-HARP color camera which uses this newly-developed pickup tube has higher sensitivity than human vision (2000 lux, F/110 equivalent), negligible low lag, and a limiting resolution of over 700 TV lines. It will be a powerful tool in emergency news gathering at night, the production of scientific programs, and other applications.

Improvement of the quantum efficiency of the new super-HARP image sensor

The New Super-HARP image sensor, which relies on avalanche multiplication in a photoconductive film made mainly of amorphous selenium, is ultra-high sensitive. The sensor has already ben used to film very dark scenes, however in such a situation, shot noise due to the quantum characteristics of light becomes a serious problem. Increasing the quantum efficiency of the image sensors can reduce shot noise. The quantum efficiency of the New Super-HARP sensor has been improved to obtain an even better picture. To increase the quantum efficiency for green incident-light two improvements have been made to the amorphous selenium film. The first is doping the film with a suitable amount of tellurium on its incident-light side. The sensor is reducing the lithium- fluoride-doped layer to about 60 percent of the thickness of the conventional film. The improved version of the New Super-HARP Film has higher quantum efficiency. Its quantum efficiency at a wavelength of 540 nm was evaluated to be double that of the conventional film. Shot noise is reduced by three dB, that is, the S/N is improved by three dB.