JPS5814753B2 - photoconductive target - Google Patents

Description

Detailed Description of the Invention The present invention provides a cadmium selenide layer, a cadmium sulfoselenide layer, a mixture layer of cadmium sulfide and cadmium selenide, a solid solution layer or a mixture layer of cadmium telluride and cadmium selenide, or a layer of zinc selenide and selenide. The present invention relates to a photoconductive target using a solid solution layer or a mixed material layer of cadmium chloride.

It is known to apply photoconductive targets with cadmium selenide layers or cadmium sulfoselenide layers or mixture layers of cadmium sulfide and cadmium selenide to image pickup tubes, such as vidicons.

For example, a photoconductive target using cadmium selenide has the following structure.

That is, as shown in FIG. 1, a signal electrode 12 made of a transparent conductive film is provided on one side of a face plate 11 made of light-transmitting glass, and a cadmium selenide layer 13 is provided on this signal electrode 12.
(CdSe), and on this layer 13, an insulator layer 14 of Sb2S3, Sb2Se3, As2S3, As2Se3, or ZnS having a specific resistance of 106 to 1014 is provided as an insulator.

Further, FIG. 2 shows a target in which a selenium oxylate layer or a mixture layer 15 of selenium oxylate and cadmium oxide is provided between the CdSe layer 13 and the insulator 14.

An example of a selenium oxyacid salt is cadmium selenite (CdSe03).

However, FIG. 3 shows a case in which an application has already been filed, in which a selenium oxysalt layer or a mixture layer 16 of selenium oxysalt and cadmium oxide is provided in an island shape between the CdSe layer 13 and the insulating layer 14. It is a target.

All of the targets obtained in this way have extremely high photoelectric sensitivity, which is more than 20 times that of the commonly used antimony trisulfide photoconductor, and is no problem when compared with the sensitivity of targets using lead monoxide. The less the better.

This evaluation has been recognized by broadcast station engineers, and the characteristics are particularly good, with almost no burn-in or dark current observed.

However, even in such conventional targets, there are still some deficiencies, especially in terms of afterimage characteristics, and improvement thereof has been desired.

The present invention has been made in view of the above points, and an object of the present invention is to provide a photoconductive target that further improves the afterimage characteristics among the characteristics of a photoconductive target mainly composed of cadmium selenide.

Hereinafter, the present invention will be explained in detail with reference to Examples.

As shown in FIG. 4, a cadmium selenide photoconductor layer is provided on a transparent conductive film 12 deposited on one side of a face plate 11 made of optically transparent glass.

That is, a cadmium selenide layer 13 and a cadmium selenite layer 16 are provided.

The cadmium selenite layer shows an example of an island-like layer.

Furthermore, in a vacuum higher than 2 x 10-3 Torr (e.g. 2
x 10-5 Torr high vacuum) with a thickness of 0.5μ, for example.
A solid layer 21 of arsenic triselenide (As2Se3; hereinafter referred to as As40Se60) is provided before and after the evaporation,
Furthermore, 2×10-1 to 2×10-2 Torr (e.g. 0
．． A porous layer 22 of arsenic triselenide is provided, which is deposited in a low vacuum argon atmosphere at a pressure of 2 Torr.
A second solid layer 23 of arsenic triselenide deposited in a high vacuum of 10@-5 Torr to a thickness of approximately 1.5 microns, for example, is provided to form a photoconductive target.

It has been found that in a photoconductive target on which a porous layer as shown in FIG. 4 is formed, the afterimage characteristics are improved as shown in FIG. 5 compared to a photoconductive target on which no porous layer is formed.

In FIG. 5, the solid line indicates the case where there is a porous layer, and the dotted line indicates the case where there is no porous layer.

The example in the figure is an example of an 18 mm tube, and in the conventional method, when the signal current is 50 nA, the third field of attenuation is 15 to 2
0%, and the third field of rise is 15-25%, whereas in the target of the present invention, the third field of decay is 8%.
~12%, rising third field 50-75%
will be improved.

The improvement is particularly remarkable in the afterimage at the beginning of the image.

Conventionally, it has been known that the afterimage characteristics of a vidicon target using antimony trisulfide (Sb2S3) are improved by combining a porous layer and a solid layer, and the target of the present invention also has a similar effect due to the porous layer. it is conceivable that.

However, the present inventors have found that, regarding the combination of the porous layer of arsenic triselenide described above and the solid layer and porous layer made of other arsenic-selenium materials described later, the following points are different from the example of antimony trisulfide. I found something different.

In other words, in the case of a target mainly made of normal antimony trisulfide, if a solid layer-porous layer-solid layer is formed on a Nesa film (Sn02 film) that becomes a transparent signal electrode on one side of a glass substrate, a solid layer is formed. As is well known, the afterimage characteristics are improved compared to a single target.

However, in this example of antimony trisulfide, the porous layer is used as a layer having a photoelectric conversion function for incident light.

In contrast, in the present invention, the layer that performs photoelectric conversion on incident light is only cadmium selenide, and the arsenic triselenide layer formed on top of it is used as an insulator layer that does not have the role of photoelectric conversion. This is a porous layer.

In the conventional example of antimony trisulfide, the photoelectric conversion layer, which is the part that is sensitive to light, is a porous layer, which not only improves the afterimage characteristics but also changes the spectral characteristics.

The solid layer of antimony trisulfide is usually sensitive to the long wavelength side of red, and the porous layer is usually more sensitive to the shorter wavelength side than the solid layer, and by using both together, it is possible to obtain spectral characteristics over the entire visible light range. There is.

In the case of the present invention, a porous layer is not provided in a layer having a photoelectric conversion function, but is applied to a portion that performs a so-called photoelectric accumulation function, and only afterimages can be improved without changing spectral characteristics.

One of the inventors of the present invention, together with other inventors, proposed that in a target having a structure as shown in Fig. 1, in order to make the specific resistance of the insulating layer a desired value, a porous layer of a low-resistance material was used to increase the resistance. However, in the present invention, the afterimage characteristics are improved by forming a porous layer including a material having a sufficiently high resistance.

The following fact was also found to be different from the antimony trisulfide vidicon example.

When arsenic triselenide is deposited as a solid layer on a SnO2 film,
As one of the inventors has already reported, it becomes a storage type vidicon (Japanese Journal of
Applied Physics Volume 6, Issue 7 875
~882 pages 1967).

Instead of the solid layer of arsenic triselenide, the layers shown in Figure 4 except for the cadmium selenide layer and the cadmium selenite layer, that is, the solid layer of arsenic triselenide, the porous layer, and the solid layer are replaced with glass. The target formed on the substrate-nesa film does not perform normal vidicon operation, but exhibits the characteristics of a storage type vidicon as shown by the dotted line in FIG.

When light is irradiated at time t=to, the signal current increases with the irradiation time, and when the light is cut off at t=to+T after an appropriate time, the signal current does not return to its original value but follows a slow attenuation curve over a long period of time. draw.

Even if a porous layer is used in combination, the K afterimage characteristics will not be improved as in the usual antimony trisulfide vidicon.

However, in the target with the configuration shown in Figure 4, when light irradiation is started at t=to, a certain signal current value is reached in an extremely short period of time, and when light is cut off at t-=to+T, the signal current value is reached within an extremely short period of time. Returns to the original dark current value.

This is observed in more detail in Figure 5 above.
Afterimage improvement is realized by a porous layer.As mentioned above, when an insulating layer is formed on a photoelectric conversion layer mainly made of cadmium selenide, afterimage characteristics can be improved by making a part of the insulating layer a porous layer. It can be improved.

Materials that make this effect possible are not limited to the arsenic selenide (As40Se60) mentioned above, but also AS60Se40, As50Se50As36Se, etc.
It is effective for materials with an appropriate molar ratio of As and Se, such as 70, AS20Se80.

The ratio of As and Se is AS55Se45, AS52Se4
Of course, a number such as 8 is also fine.

However, if As exceeds Se, As may not react sufficiently with Se, and As alone may become liberated and cause harm.
It's very practical.

When the molar ratio of Se increases, the release of As alone is not a problem, but rather the problem is deterioration of image quality due to crystallization of selenium after forming a thin film.

Therefore, in order to prevent the crystallization of Se, the molar ratio of As may be about 2.

In addition, not only As-Se type but also As-S type, As-Te type
system or As-S-Se, As-S-Te, As-S
Formation of a porous layer is also effective for e-Te material.

Note that the characteristics shown in FIG. 6 often occur with materials mainly composed of As-Se.

Although arsenic triselenide is mainly used as the insulating layer in the structure shown in FIG. 4, the solid layer and the porous layer may be made of different materials.

For example, the first solid layer contains arsenic triselenide (As40S).
e60), arsenic diselenide (AS50Se) is used in the porous layer.
50), arsenic triselenide (As40) is added again to the second solid layer.
Se60) may also be used.

Arsenic triselenide has many manufacturing advantages because it is easier to control the formation of a porous layer than arsenic triselenide.

Furthermore, the materials may be combined in any manner, such as in the case where an As-S solid layer is formed on an As-Se solid layer and a porous layer.

Furthermore, the combination is not limited to a solid layer-porous layer-solid layer, but a solid layer-porous layer as shown in FIG. 7, or a porous layer-solid layer as shown in FIG. As shown in FIG. 9, the structure may be a porous layer-solid layer-porous layer.

Further, solid layers and porous layers may be alternately stacked.

The results of various experiments show that when a solid layer is deposited on a porous layer, the afterimage characteristics are significantly improved.

In addition, in the case of the porous layer-solid layer order, it was observed that when the solid layer was deposited, a rice-grain-shaped layer was formed in the vertical direction with part of the porous layer as the nucleus.

In this case, if the porous layer is extremely thick and a rice grain layer is formed on it, it is necessary to set the target voltage of the vidicon extremely high (for example, 100 V or more) in order to obtain an image, which is not practical.

If there is a small amount of remaining porous layer and a grain-like layer is formed by depositing a solid layer on top of it, the target voltage will be within the practical range of 50V or less, and an image pickup tube with good afterimages will be obtained. .

In the above explanation, as shown in Fig. 4, a photoelectric conversion layer mainly made of cadmium selenide and an island-shaped cadmium selenite layer formed thereon were used as an example. It is clear that the present invention can be applied both to the case where only a layer mainly consists of cadmium selenide, or to the case where a cadmium selenite layer is formed on a layer mainly composed of cadmium selenide as shown in FIG.

An example is shown in FIG. The insulating layer is a solid layer - a porous layer -
This is an example of a solid layer.

In the embodiment of the composite target according to the present invention, an example was described in which cadmium selenide was used in the first layer.
It may be a solid solution (cadmium sulfoselenide) containing 1/2 of cadmium selenide or a mixture.

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

Further, it may be a solid solution or a mixture containing cadmium telluride and cadmium selenide.

Alternatively, each layer of cadmium telluride and cadmium selenide may be superimposed.

Further, it may be a solid solution or a mixture containing zinc selenide and cadmium selenide, or it may be a layer in which zinc selenide and cadmium selenide are superimposed.

Further, any other material may be used as long as it forms a solid solution with cadmium selenide, or can be mixed with or superimposed with cadmium selenide.

For example, 99.999% high purity cadmium selenide can be used as is for these composite targets.

Alternatively, in addition to thallium, one or more of well-known impurities such as copper, gold indium, gallium, aluminum, halogen alkali metals, and alkaline earth metals may be included.

The role of the first layer, which is mainly made of cadmium selenide, is to obtain photosensitivity, similar to the conventional target structure, and light absorption takes place in this first layer.

In this sense, this layer can be called a photoelectric conversion layer.

Although cadmium selenite was used in the above embodiments, cadmium oxide may also be mixed therein.

In addition, complex intermediate compounds consisting of cadmium, selenium, and oxygen, such as Cd3Se4O11 (3Cd-SeO3
・SeO2) may be mixed with cadmium selenite.

In addition to arsenic-selenides such as arsenic triselenide and arsenic-sulfides such as arsenic trisulfide mentioned in the examples, the materials for the porous layer include germanium sulfide, germanium selenide, thallium sulfide, thallium selenide, Bismuth trisulfide, bismuth triselenide, zinc selenide, zinc sulfide, cadmium telluride, antimony trisulfide, antimony triselenide,
Materials used include calcium fluoride, magnesium fluoride, aluminum fluoride, sodium fluoride, cryolite, and lead oxide.

In addition, to form a porous layer, vapor deposition in an argon atmosphere as described in the examples is effective, but not only argon but also nitrogen or other inert gases may be used, and even oxygen may be included. .

As described above, by applying a porous layer to a layer that does not have a photoelectric conversion function, an image pickup tube with excellent afterimage characteristics can be obtained.

[Brief explanation of the drawing]

Fig. 1 is a cross-sectional view for explaining a conventional photoconductive target using cadmium selenide, Fig. 2 is a cross-sectional view showing another structure of Fig. 1, and Fig. 3 is another structure of Fig. 1. FIG. 4 is a cross-sectional view for explaining one embodiment of the photoconductive target according to the present invention, and FIG. Figure 6 is a characteristic curve diagram showing a comparison of the afterimage characteristics of a photoconductive target of the present invention consisting of a photoelectric conversion layer mainly made of cadmium selenide and arsenic selenide, and a photoconductive target consisting only of arsenic selenide. Characteristic curve diagrams showing a comparison of photoresponse characteristics; Figures 7, 8, and 9 are cross-sectional views showing other structures in Figure 4; Figure 10 shows the present invention applied to the target in Figure 1; FIG. 11 is a diagram showing an embodiment in which the present invention is applied to the target shown in FIG. 2. DESCRIPTION OF SYMBOLS 11... Face plate, 12... Transparent conductive film 13... CdSe layer, 14... Insulator layer, 15...
・CdSeO3 layer, 16... Island-shaped CdSeO3 layer,
21... Solid layer of As40se60, 22... As
Porous layer of 40Se60, 23...As40Se60
solid layer.

Claims (1)

[Scope of Claims] 1. A photoconductor layer that performs photoelectric conversion of incident light, and an insulator layer provided on the photoconductor layer that does not have a photoelectric conversion function of incident light, the insulator layer 1. A photoconductive target having a laminated structure of at least a solid layer formed by high vacuum evaporation and a porous layer formed by low vacuum evaporation. 2. The photoconductive target according to claim 1, wherein the insulating layer has a laminated structure of a solid layer, a porous layer, and a solid layer. 3. The photoconductive target according to claim 1, wherein the insulating layer has a laminated structure of a porous layer, a solid layer, and a porous layer. 4. The photoconductive target according to claim 1, wherein the insulating layer is a solid layer of As40Se60, a porous layer of As50Se50 provided on the solid layer, and a solid layer of AS40Se60 provided on the porous layer. 5 As a photoelectric conversion layer, cadmium selenide, cadmium sulfoselenide, a mixture layer of cadmium sulfide and cadmium selenide, or a solid solution layer or mixture layer of cadmium telluride and cadmium selenide, or a solid solution layer of zinc selenide and cadmium selenide, or A photoconductive target according to claim 1, which uses a mixed material layer. 6 As a porous layer, arsenic-selenide, arsenic-sulfide, arsenic-telluride, arsenic-sulfur-selenium compound, arsenic-sulfur-tellurium compound, arsenic-selenium-tellurium compound, germanium sulfide, germanium selenide, sulfide Thallium, thallium selenide, bismuth trisulfide, bismuth triselenide, zinc selenide, zinc sulfide, cadmium telluride, antimony trisulfide, antimony triselenide, calcium fluoride, magnesium fluoride, aluminum fluoride, sodium fluoride The photoconductive target according to claim 1, which uses cryolite or lead oxide.