JPS5826832B2 - Method for manufacturing photoconductive targets - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a photoconductive target suitable for a vidicon type image pickup tube having photosensitivity even in the infrared region.

One of the present inventors, together with other inventors, has already commercialized an imaging tube called Carnicon (trade name) using a photoconductive target of cadmium selenide.

In this target, arsenic trisulfide or arsenic triselenide is formed on a cadmium selenide layer to form a composite target, and a high sensitivity with a quantum efficiency close to Kl in the visible light region can be obtained, and it can be used for imaging from black and white to color. Extremely useful as a pipe.

The long wavelength end of the spectral sensitivity is around 700 mμ, and there is almost no sensitivity in the infrared region of longer wavelengths than this.

Generally, in a color display, if the photoconductive target is sensitive to the infrared region, false signals will be generated by infrared light in each of the blue, green, and red channels, resulting in an image with a color tone different from that perceived by humans. is obtained.

For this reason, in color TV cameras, an infrared cut filter is provided in the incident optical path to remove harmful infrared light.

Calnicon, which has almost no infrared sensitivity, is suitable as a color image pickup tube.

On the other hand, in black-and-white imaging, it is necessary to have high sensitivity to visible light, and it is desirable that the quantum efficiency of Calnicon be close to 71.

However, photosensitivity not only in the visible region but also in the near-infrared to infrared region is required for black-and-white imaging.

The field of black-and-white imaging is centered around ITV cameras for surveillance, and in recent years, for example, imaging under low illumination, such as for monitoring inside expressway tunnels, has become popular.

In imaging at such low illuminance, visible light decreases and infrared light increases relatively, so light sensitivity in the infrared region, which is harmful in color imaging, is required.

Therefore, IT for black-and-white monitoring, mainly for imaging in low light.
It is desirable that the photoconductive target of the V-camera's imaging tube be infrared sensitive.

The present invention has been made in view of the above points, and provides a photoconductive target that also has infrared sensitivity.

That is, for example, a method is obtained in which a CdSe layer is heat-treated in an inert gas atmosphere containing Se or Se and oxygen, a CdTe layer is formed, and then a CdSe layer is heat-treated in an inert gas atmosphere containing Te or Te and oxygen.

An example of this will be described below with reference to the drawings.

Light-transmitting plate, such as a light-transmitting glass face plate 1
A cadmium selenide layer is deposited on the transparent conductive film 2 to a thickness of, for example, 1.2 μml.

In this vapor deposition, it is appropriate to use an inert gas such as nitrogen or argon, or an inert gas containing oxygen as the vapor deposition atmosphere.

Further, it is preferable to perform the deposition while keeping the substrate temperature at an appropriate temperature of lOOoC to 350°C.

After vapor deposition, in order to increase the photosensitivity, the main component is an inert gas such as argon or nitrogen, and 4
1 at a suitable temperature between 50°C and 700°C, e.g. 600°C.
After 5 minutes of sintering, the cadmium selenide sintered film 3
form.

In this sintering step, an appropriate amount of oxygen gas may be present to facilitate crystal growth.

The steps up to the glass face plate 1, the transparent conductive film 2, and the cadmium selenide sintered film 3 are similar to the conventional manufacturing method of a cadmium selenide photoconductor for photoconductive storage.

In the present invention, a cadmium telluride layer is further deposited on the sintered film 3.

In this deposition, the substrate temperature ranges from loo'c to 400°C.
C., for example 250.degree.

The cadmium telluride layer 3 is formed to a thickness of, for example, 0.5 μm in a high vacuum of, for example, 2×10 −5 Torr.

The atmosphere in which the cadmium telluride layer 3 is deposited is not limited to a high vacuum, but may be a low vacuum, or may be an inert gas atmosphere such as nitrogen or argon.

The thickness of cadmium telluride is not limited to a 0.5μ door, and may be, for example, a 5μ door for 200 people.

After forming a cadmium telluride vapor-deposited film, it is heated at an appropriate temperature of 4000C to 700C in an atmosphere containing tellurium vapor, with an inert gas such as argon or nitrogen as the main component.
For example, a sintering process is performed at 600° C. for 15 minutes to form the cadmium telluride sintered film 4.

The sintered cadmium selenide film 3 and the sintered cadmium telluride film 4 form a photoconductive film that performs photoelectric conversion.

An appropriate amount of oxygen gas may be present in the second sintering process using the tellurium atmosphere.

Compared to selenium, tellurium has a stronger bond with oxygen, so if a large amount of oxygen is added, Te025Te03
．． or CdT e03 is formed on the photoconductive film and appears as minute black dots on the imaging screen, deteriorating the image quality, so care must be taken.

On this photoconductive film, a high resistance film 5 of arsenic trisulfide having a thickness of, for example, 0.4 μm or arsenic trisulfide having a thickness of, for example, 1.5 μm is formed as in the conventional cadmium selenide composite target. A composite target 6 is obtained.

A comparative example of the sensitivity in the near-infrared to infrared region of an 18ψ prototype tube having a target of the present invention and an 18ψ tube having a conventional target will be shown below.

The so-called white light sensitivity, which is the signal output current when the target surface illuminance is 11ux using a standard light source with a light source temperature of 2850°, is 160 nA in the conventional tube, but the sensitivity is extremely large, for example, 320 nA in the prototype tube of the present invention. .

In this measurement, IR-
Comparing only the infrared sensitivity when using an optical filter called DIB, we can see that with the conventional tube, almost no signal is obtained with OnA, whereas with the prototype tube of the present invention, 35n is obtained.
A signal is obtained.

It can be seen that the sensitivity in the near-infrared to infrared region is increased by the sintered cadmium telluride film.

Regarding other characteristics of image pickup tubes, the dark current is 1n for conventional tubes.
Although there is a tendency for the test tube of the present invention to slightly increase the current by several nA, it satisfies the characteristics as an image pickup tube for a black-and-white ITV camera.

As a target with a similar structure to the photoconductive target of the invention, Advancesin Electroni
csand Electron Physics Vo
l, 4OA (academic Press') 3
Cd5-CdTe-As2Se3 on pages 35 to 348
Heterozygous targets have been reported.

However, it differs from the target of the present invention in the following points.

That is, the photoconductor material that performs the photoelectric conversion function and its form are different.

In the present invention, it is mainly a cadmium selenide sintered film,
This is a polycrystalline film, whereas the cited target is made of cadmium sulfide and is single crystal, which is a big difference.

In the cited example target, a CdS single crystal target has a photosensitivity peak in green at 520 nm, which is at the absorption edge of CdS, and the lack of sensitivity in the red to near-infrared region is increased using cadmium telluride (CdTe). I feel it.

In the target of the present invention, the visible range up to red is due to the photosensitivity of the polycrystalline cadmium selenide sintered film, and the non-visible range from near infrared to infrared is sensitized with cadmium telluride. There is.

In addition, in the cited example target, after CdTe is deposited, an oxidation process is performed at 450°C for 10 minutes while flowing argon and oxygen gas, and then annealing is performed at 450°C for 20 minutes while flowing argon gas. .

The present invention is characterized in that sintering is carried out in an atmosphere of tellurium vapor, and the gas atmosphere must be kept stationary in order to maintain the tellurium vapor atmosphere.

In the target of the present invention, cadmium telluride is transformed into a polycrystalline film by sintering with tellurium vapor, making it possible to achieve high photosensitivity.

In the cited example, 7. O
With a photocathode area of x5.2 mm, a sensitivity of about 160 nA is obtained for a surface illuminance of 8 lux.

In the present invention, the above-mentioned approximately 320 n is applied to a surface illuminance of 1 lux in an area of 6.6 x 8.8 mr7+2.
A has a high sensitivity, and the tellurium sintering process is an extremely effective means of sensitization.

In addition, depending on the manufacturing conditions of the photoconductive target of the present invention, the sensitivity to visible light, especially blue light and green light, due to the sintered film of cadmium selenide may be lower than the quantum efficiency of the conventional cadmium selenide-arsenic triselenide. Although the sensitivity may be reduced to about 1/2 or 1/3 compared to the sensitivity close to sol, the sintered film of cadmium telluride effectively improves the sensitivity from near-infrared to infrared. As a result, the overall sensitivity to white light is 300 nA to 350 nA, which is often higher than conventional tubes. In addition, after evaporating cadmium telluride on the sintered cadmium selenide film, the same process as the cited example target is used. The target treated at 450° C. in the absence of tellurium vapor provided infrared sensitivity but had a dark current of several tens of nA or more, making it useless.

As described above, according to the target of the present invention, even higher sensitivity can be obtained due to the interception that is different from that of the reference example target.

In the cited example, cadmium telluride is applied directly onto the single crystal CdS, which seems to be advantageous because the initial sintering step with selenium as in the present invention is omitted, but extremely careful consideration and equipment are required for the formation of the single crystal. Moreover, it is necessary to attach a signal electrode of a thin metal film to the opposite side of the obtained single crystal plate and then bring it into contact with the transparent conductive film on the glass substrate, which increases the number of steps.

It is easier to form the film at a desired location and at a desired thickness by direct vapor deposition as in the present invention, and is suitable for mass production.

The photoconductive target of the present invention consists of two main steps: first, evaporation of cadmium selenide and sintering with selenium; second, evaporation of cadmium telluride, sintering with tellurium, and formation of a photoelectric conversion layer. Divided.

It may be possible to simplify this by superimposing cadmium selenide and cadmium telluride and sintering with selenium or tellurium, or if sintering with selenium, almost no infrared sensitivity can be obtained. First, when tellurium is used for sintering, the overall sensitivity is usually lower than that of conventional tubes, and the purpose cannot be achieved.

Note that without the cadmium selenide sintered film, the photosensitivity would be low and the dark current would be 10 nA or more, which would not meet the purpose.

In the target of the present invention, as described above, the deposition and sintering steps are increased compared to the conventional method, or a highly sensitive photoconductive target whose sensitivity is reliably extended to the near-infrared region can be obtained.

In the above embodiment, an example was described in which cadmium selenide was used in the first photoconductive layer on the transparent conductive film, but an appropriate amount of cadmium sulfide, for example, a weight ratio of cadmium sulfide/cadmium selenide 1/2, was used. It may be a solid solution (sulfo-cadmium selenide) or a mixture containing.

Alternatively, layers of cadmium sulfide and cadmium selenide may be superimposed.

Further, a solid solution or mixture of cadmium selenide and cadmium telluride, or a layer in which cadmium selenide and cadmium telluride are superimposed may be used.

Furthermore, it may be composed of the kings of cadmium selenide, cadmium telluride and cadmium sulfide.

In any case, the deposited film of II-Vl group photoconductive material is sintered in a first sintering step in a selenium atmosphere, cadmium telluride is evaporated, and then the deposited film is subjected to a second sintering step in a tellurium atmosphere. A photoconductive target with external sensitivity can be provided.

For example, if a cadmium telluride vapor-deposited film is sintered in a selenium atmosphere at 600°C for 30 minutes instead of cadmium selenide, the sintered film will show some differences in the diffraction peaks, but the results of X-ray diffraction will be Almost changes to cadmium selenide film.

Therefore, the object of the present invention can be achieved by depositing cadmium telluride thereon and performing tellurium sintering in the second step.

In the example of a cadmium sulfide vapor-deposited film, most of the film is converted to cadmium selenide in the first step, and infrared sensitization can be achieved by vapor-depositing cadmium telluride using this soil and sintering tellurium in the second step.

The light sensitivity from near-infrared to infrared depends on the thickness of the deposited cadmium telluride layer, the sintering temperature and time in tellurium sintering, and the concentration and vapor pressure of tellurium vapor.

Infrared sensitivity increases depending on whether the vapor pressure of tellurium is high or the sintering time is long, but the visible sensitivity may decrease, so depending on the purpose of use, the sintering temperature, amount of tellurium, and sintering time are There is a need to determine it appropriately.

By sintering the tellurium, the cadmium waum telluride vapor deposited film is mainly sintered, but some of the tellurium vapor also reaches the cadmiwaum selenide sintered film, so that the cadmiwaum selenide layer may also change.

In FIG. 1, for convenience of explanation, the photoconductive layer is depicted as being clearly separated into two layers, but it goes without saying that in an actual target, the boundary may not be sharp.

The sintered film becomes a photoelectric conversion layer, but this layer contains various oxides such as CdSeO3, C
dTeO3 and Cd503. CdO,5e02.

A trace amount of TeO2 or the like may be included, or a trace amount of selenium or tellurium in the atmosphere may remain.

In addition to the arsenic-sulfides such as arsenic trisulfide and arsenic-selenide such as arsenic triselenide mentioned in the examples, the high-resistance materials formed on the photoelectric conversion layer include germanium sulfide, germanium selenide, kurium sulfide, High resistance materials such as taliwum selenide, bismuth trisulfide, bismuth triselenide, zinc selenide, zinc sulfide, cadmium telluride, antimony trisulfide, and antimony triselenide are used.

These layers may be formed not only of a single layer of a single material, but also of a multilayer structure consisting of multiple layers of two or more types of materials.

These layers may be solid layers deposited in vacuum, porous layers deposited at a low height, or a combination thereof.

Even if these layers are made of photoconductive materials, most of the light absorption takes place in the photoelectric conversion layer, so it does not have a large effect on photosensitivity.As mentioned above, it is a type of n-VI group compound. Alternatively, a vapor deposited film of multiple kinds of solid solutions or mixtures or a plurality of superimposed vapor deposited films are heat-treated at temperatures ranging from 400°C to 700°C in an atmosphere of selenium or an inert gas containing selenium and oxygen. Cadmium telluride is formed by vapor deposition and then heated for 400 min in an inert gas atmosphere containing tellurium or tellurium and oxygen.
A high-sensitivity photoconductive target having infrared sensitivity can be obtained by using a composite target comprising a photoelectric conversion layer heat-treated at a temperature of .degree. C. to 700.degree. C. and a high-resistance material layer formed on this layer.

[Brief explanation of drawings]

FIG. 1 is a sectional view of one embodiment of a photoconductive target according to the present invention. 1...Glass face plate, 2...
...Transparent conductive film, 3... Film obtained by sintering a cadmium selenide vapor-deposited film in a selenium atmosphere, 4...
High resistance material layer, 5... Photoconductive target, 4.
... Film obtained by sintering the tellurium-deposited film in a tellurium atmosphere, 5 ... High-resistance material layer, 6 ...
...Photoconductive target.

Claims (1)

[Claims] 1. A step of forming one kind of vapor deposited film of I-Vl group compound, a vapor deposited film of plural kinds of solid solution or mixture, or a plurality of superposed vapor deposited films of I-Vl group compound on the transparent conductor layer to obtain a photoconductor layer. Then, the photoconductor layer obtained in this step was heated at a temperature of 4 ℃ in an atmosphere of selenium or an inert gas containing selenium and oxygen.
A first heat treatment step at 00°C to 700°C, a step of forming a cadmium telluride layer on the sintered layer obtained in this step, and a step of forming a cadmium telluride layer obtained in this step into tellurium or tellurium. and a step of performing a second heat treatment at a temperature of 400° C. to 700° C. in an inert gas atmosphere containing oxygen, and a step of forming a high-resistance material layer on the layer obtained in the step. A method for manufacturing a photoconductive target characterized by: