Saburo Ataka

Photoconductive imaging using hydrogenated amorphous silicon film

Highly resistive hydrogenated amorphous‐silicon film has been fabricated and examined as blocking‐type photoconductive target of a vidicon‐type image pickup tube. The results indicate that this novel silicon vidicon has many advantages over conventional ones.

Laser‐stimulable transparent CsI:Na film for a high quality x‐ray imaging sensor

Transparent films, which can be stimulated by laser beams after x‐ray irradiation, have been searched to improve the spatial resolution of digital x‐ray imaging sensors. As a result, evaporated CsI:Na films are found to be efficiently laser stimulable around 77 K. The modulation transfer function (MTF) of the film is evaluated using a scanning Ga1−xAlxAs semiconductor laser. The high MTF value (57% at 2 1p/mm), strong x‐ray absorption, and high stimulation efficiency of the film ensure a high quality sensor for digital radiography.

Amorphous Silicon Image Pickup Devices

Reactively sputtered amorphous silicon film is used as a photoconductive target of the vidicon type image pickup tube. Variation of tube characteristics with the hydrogen partial pressure in the discharge gas during sputtering are investigated. The results indicate that hydrogenated amorphous silicon films prepared in hydrogen partial pressures of 1~2×10-3 Torr are suitable for image pickup tubes. This amorphous silicon vidicon has several excellent characteristics: better sensitivity of about twice that of the conventional tubes, high resolution, little after-image, and no blooming.

AsH3 cracking characteristics in gas source molecular beam epitaxy

A time dependence of AsH3 cracking characteristics in gas source molecular beam epitaxy using metalorganic and hydride gases was found. AsH3 flow for about 1 hour was needed to create a stationary state in the cracking characteristics. During this transitional time, some arsenic, decomposition products of AsH3, was trapped in the cracking cell, and there was a limit to the amount of arsenic that was trapped. The amount of arsenic was limited by the existence of AsH3 in the cracking zone which hindered the trapping of arsenic. The arsenic trapping might be caused by chemical reactions between arsenic and the cracking cell.