Sensitivity of an evaporated PbS cell depends not only upon the content of atmospheric oxygen in the cell layer, but upon the temperature of the substrate during the deposition. Two methods of preparing the PbS layer are described in regard to the cell sensitivity. In one method, termed A-method, the substrate is kept at about 270°C by a jet of air before the deposition is begun; in the other, termed B-method, the deposition is begun on the substrate when its temperature is 400°C, then the substrate is gradually cooled to about 250°C by a jet of air. In both methods, the deposition is processed at 0.7_??_0.9mmHg pressure. Optical properties of A-type cell by A-method are considerably different from those of B-type cell by B-method: the peak of sensitivity of the former is on the shorter wavelength side of, and a few times higher than, that of the latter. As for the time constant, B-type cell's is 150 μsec. on the average which is twice as good as A-type cell's 300 μsec. average. However, the average values of NEP of A-type and B-type cells are 6.6×10-12 W and 1.3×10-11W respectively. For spectrophotometric measurement, the time constant needs not to be very small, therefore the deposition of PbS on a substrate of comparatively low temperature as in A-method seems feasible for preparing a high sensitive photoconductive cell.
Anomaly and anisotropy of resistivity of evaporated silver film vacuum-deposited on glass substrate by oblique incidence are dealt with. Resistivity of the film shows anomaly at incident angles of about 30°_??_35°. This phenomenon seems to be related to how the crystals grow during deposition. The difference between the values of resistivity measured in two directions, parallel and perpendicular to the vapor stream, is explain-ed as caused by self-shadowing of the growing crystals.
Germanium thin films obliquely deposited in vacuum have been found to be photoelectrically anisotropic, viz., when they are illuminated by light, a high photo-voltage appears on them along the direction of deposition. A further study is made on this anisotropy. If the illumination is by a polarized light, the intensity of transmitted light rests with the orientation of electric vector of the incident light, which implies that the absorption coefficient of the film has different values in two directions, parallel and perpendicular to the direction of deposi-tion, with the result that the transmitted light becomes elliptically polarized when a plane-polarized light falls on the film. This is explained by self-shadowing that occurs during the oblique deposi-tion: the growing crystallites prevent the impinging atoms from reaching the substrate where the crystallites cast shadows leaving there undeposited areas. Hence, in forming a film, all the crys-tallites grow long, crosswise to the direction of deposition. A light in passing through such an obliquely deposited film of oriented long crystallites suffers the greatest absorption when the electric vector is parallel to the long axes of the crystallites. This is the reason why an obliquely deposited film shows anisotropy, which is ascertained by the obliquely deposited germanium film. During its deposition in vacuum, its electric conduction has been observed to be also anisotropic.
For this investigation, CdSxSe(1-x) single crystals (0_??_x_??_1) prepared by the vapor phase method are used. Lattice constants and spectral response peaks of these crystals vary continuously with the composition-ratio x. Photocurrent-light intensity characteristic, dark current-temperature characteristic, thermally stimulated current, and thermal quenching of photo-current are measured. From the measurements of thermally stimulated current, CdS, CdSxSe(1-x) and CdSe were found to have electron trapping levels at nearly equal energy-separations (_??_0.3eV) from the bottom of the conduction band. Dark resistivity of CdSxSe(1-x) crystals was about 108 ohm-cm, while photo-resistivity for 600 lux light of an incandescent lamp was about 103_??_104 ohm-cm at room temperature. Hole trapping levels were found lying in the vicinity of 0.5_??_0.7eV above the top of the valence band.
An extensive investigation of factors affecting the evaporation of Mg from Ni core metal is carried out by the heating method in high vacuum. The evaporation is affected not only by the quantity of Mg contained in Ni and surface treatment of the core metal, but also by the manu-facturing conditions of the core metal as regards material, deoxidization and melting atmosphere. The evaporation of Mg from oxide coated Ni core metal depends on how the coating and evacuation are processed. If these processes remain the same, further addition of 2-4 percent W to the core metal lowers the evaporation. Such evaporation characteristics seem to relate to the chemical reaction of Mg with oxide compound, such as NiO, in the Ni core metal.
For preparing photoconductive CdS thin films, there are various methods-evaporation method, sputtering method and others-by which, however, sufficiently high-sensitive photoconductors can not be produced. A new method has been devised in which CdS thin films are made in a mixture of H2S and H2 gases in an open type furnace, whereby US films of sensitivity higher than by any other method and of considerably good characteristics concerning, for example, photocurrent vs. applied voltage and photocurrent vs. excitation intensity are obtained. Photo-sensitivity of samples made by this method is almost equal to that of a sintered US cell.
A method for the preparation of molded rhenium cathodes composed of alkaline earth carbonates and rhenium metal powder is described, and the thermionic emission characteristics are examined. The values of saturated pulsed emission at 925°C and work function after the thermal activation of 50 hours at 1010°C were respectively 2A/cm2 and 1.4 eV. The behavior of these values during the thermal activation depends on the cathode temperature in preceding exhaustion process: with the rise of the cathode temperature in the exhaustion process, the saturated pulsed emission be-comes higher at the earlier stage but lower at the later stage of thermal activation. This may be ascribed to sintering of the cathode materials in the exhaustion process. The emission from this cathode is increased by the addition of ZrH2 as an activator. The resistance to oxygen poisoning of this cathoded is superior to that of the molded nickel cathode composed of alkaline earth car-bonates and nickel metal powder. In this experiment, the molded rhenium cathode had no trouble during the exhaustion and the thermal activation, therefore it is practically feasible to use rhenium metal in the combination with alkaline earth carbonates. This cathode is considered to be suitable for the application requiring heavy operation.
An experimental study has been made on the breakdown phenomena observed on alloyed sili-con p+-n junctions which have breakdown voltages in the range of 0.5 to 30 volts. When the junctions are biased in the reverse direction to breakdown, a visible light is emitted from the rectangular cross-section of their junction planes. On the samples with breakdown voltages of 3 volts or less, a faint light is seen along the entire cross-section with no photo-multiplication of carriers. The light emission seems to be due to the breakdown of Zener emission type. But on. the samples with breakdown voltages of 9 volts or more, light spots are observed at edges or pointedd parts of the junction plane accompanied with a large photo-multiplication of carriers. This light emission seems to be due to the breakdown of avalanche type. Beside the above two types of light emission, a new type of bright emission has been observed, which, despite its being not directly related to the junction itself, has a large influence upon the breakdown characteristics. The photo-multiplication factor of carriers is measured by irradiating the cross-section of the junction plane by a chopped light. On the samples with breakdown voltages of 5 to 9 volts, the factor has been found to be quite uniform over the entire area of the junction plane, and on the samples with breakdown voltages of above 9 volts, to be large at the edges or pointed parts, but hardly perceptible in the central flat area, of the junction plane.