DE1564544A1 - Photoelectric device and method for producing a photo layer therefor - Google Patents

Description

RGA 56 363 638l-66 / Kö / Bru

USerial No.507,728.
Convention date: Nov. 15 * 1965
Inventor: WMKramer

Radio Corporation of America, New York, N.Y.,

V.St.A.

Photoelectric device and method for producing a photoschioht therefor

The invention relates generally to photoconductor materials and their manufacture. In particular, it relates to a photoelectric Device and a method for producing a photo layer therefor.

It is known (see e.g. US Pat. No. 2,654,853, filed October 6, 1953) that amorphous selenium is used as the material for the photolayer photocells, image pick-up tubes and other photoelectric devices. Amorphous selenium offers the advantage of a good sensitivity (usually a quantum yield of 1) for blue light, a low dark current as well as short response and decay times, i.e. low inertia. The main disadvantage is the unfavorable spectral sensitivity with essentially insensitivity to red light and an instability that manifests itself in the fact that the

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amorphous selenium proportionally over time and with increasing temperature easily changes into the electrically conductive crystalline form. Furthermore, selenium layers show the property that at constant exposure the initial signal fades over time and that is reversible above a certain critical voltage local breakdowns occur with high dark current. Early-. re "attempts to have a red sensitivity and increased stability to achieve the layers by adding contaminants or by changing the substrate, had one disadvantageously large increase in the inertia or the dark current result.

It is known ("Journal of the American Optical Society", Volume 42, 1952, p.221) to use selenium layers in the form of xerographic plates for electrophotographic purposes, in which an increased sensitivity to red is achieved by adding about 7% tellurium to selenium as well is obtained by using a heated support. However, it was found that with increasing tellurium content, especially in the range from $ 6 to $ 8 tellurium, the

Sheet resistance decreases rapidly.

The purpose of the invention is to prevent the use of tellurium additives in selenium layers or selenium films, which are suitable for use in photoelectric devices such as storage electrodes suitable for image pick-up tubes. In addition, the aim is to stabilize the photoelectric devices in this type of device

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layers or films of amorphous selenium used can be achieved.

According to one embodiment of the invention is a photoconductor material in the form of an alloy or a mixture

Selenium, tellurium and arsenic are provided. One of this material contain- ' Tende photoelectric device consists of a conductive electrode, on the surface of which a photo layer made of the alloy or the mixture of selenium, tellurium and arsenic is appropriate. Preferably the photoconductor alloy has a composition from 70-δΟ weight percent selenium, 17-29 weight percent tellurium and about 1 weight percent arsenic.

According to a further embodiment of the invention, the photoelectric device manufactured in such a way that in the photoshifts from selenium and tellurium the composition of the alloy or mixture in the direction from one to the other Layer surface is changed so that one in concentration graded or graduated layer is created. One embodiment of this graded layer is produced by one successively amounts of the alloy with which one an evaporator tray loaded, completely evaporated: so that on one Layer base creates a thin partial layer with essentially the percentage composition of the alloy. Afterward the charging rate is increased in such a way that the temperature of the evaporator tray and the percentage fall accordingly

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of the tellurium in the vapor-deposited layer decreases evenly. The evaporator dish is then kept at a low evaporation temperature, so that as a layer-forming material in the essential selenium is vaporized. In this way a photo layer is obtained which has a high surface on one of its surfaces Selenium concentration, with a uniform gradation or gradation of the composition between the two surfaces the selenium-tellurium mixture "or alloy.

According to a further embodiment of the invention, that surface of the layer support on which the photo layer is formed and which is adjacent to the tellurium-rich layer surface is provided with a conductive layer of the n-conductivity type, which opposes the p-conductivity type of the tellurium-rich surface of the photoslayer, for certain application purposes isc, provided. In this way, a transition or a barrier layer is obtained between the two layers of opposite conductivity type, by means of which the dark current flowing through the photo layer can be controlled and reduced.

The advantages achieved by the invention are: that a photoelectric device is obtained in which amorphous selenium with its inherent good properties as a photoconductor material and the addition of tellurium changes the spectral sensitivity of the amorphous selenium in such a way that

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that it is largely approximated to the panchromatic spectral sensitivity of the human eye. Fires stand out the photoelectric devices through improved responsiveness, thus lower inertia and greater stability of the photoconductor material.

Exemplary embodiments of the invention are described with reference to the drawing. Show it: "

Fig.l is a fragmentary partially sectioned View of an image pickup tube with a photoconductive storage electrode according to the invention;

Figs. 2, 3 and 4 are fragmentary sectional views of photoelectric Devices each with a layer according to the invention made of vitreous selenium / tellurium alloyj

Fig. 5 is a schematic representation of the production the photoelectric devices according to Fig. 1-4 usable device;

6 is a plan view of the device according to FIG. 5 in a plane corresponding to the lines 6-6 in FIG. 5J

7 shows a diagram which illustrates the difference in light absorption between a layer of vitreous selenium / tellurium alloy in which the tellurium is evenly distributed and a layer in which the tellurium content is graded. 009818/1374

Pig.l shows part of a photo-layer image pick-up tube 10 with a photoconductive storage electrode 12 designed according to the invention. The tube 10 has an elongated glass bulb 14, which is closed at one end by a transparent faceplate 16 made of glass, which is secured by means of an indium ring 18 and a clamping ring 20 is sealingly attached to this piston end. The storage electrode 12 is attached to the inner surface of the faceplate 16. At a close distance from the storage electrode 12, a mesh network 22 is stretched over one end of a tubular focusing electrode 2h. In the other end (not shown) of the piston 14, the electron beam system for generating the scanning electron beam is arranged. The electron beam is deflected over the storage electrode 12 in a grid pattern by suitable devices such as electromagnetic deflection coils (not shown) arranged outside the piston.

The storage electrode 12 contains a layer 26 of conductor material, for example in the form of a thin layer of rhodium or tin oxide with a thickness of about 6-25 8, so that it is transparent and consequently the light from the object to be picked up passes through the layer 26 _{f essentially unhindered} and reaches the photo layer 28 below. The layer thickness mentioned is also sufficient for the use of layer 26 as a conductive signal electrode or signal plate.

00901

The photo layer 28 in which the principles of the invention are embodied consists of a glassy or amorphous one Alloy of selenium, tellurium and arsenic with a thickness of approximately 0.2 to about 5 * 0 microns. Although the shift also without

Arsenic works satisfactorily, the presence of arsenic helps improve decay properties as well as stability. In a special embodiment, the layer 28 applied so that it is rich in tellurium adjacent to the electrode layer 26 in the direction of the incident light and the relative share of tellurium gradually decreases towards the other side of the layer. For example, the proportion by weight is of tellurium in the surface area adjoining the layer 26 of layer 28 about 23 $ j while it is in the surface area on the other hand is from $ 0 to about $ 10. In such a graded or graded photo layer 2 & can the percentage composition of that adjacent to layer 26 Surface area is 70-60 percent by weight selenium, 17-29 percent by weight tellurium and approximately 1 percent by weight arsenic. Quality Results were with about 76 weight percent selenium, 23 weight percent Tellurium and 1 percent by weight arsenic in the

26th

Layer / adjacent surface area of the glassy alloy layer 28 obtained. If arsenic is not used, one can increase the selenium content by approximately 1 percent by weight.

The arrangement of the two layers 26 and 2δ according to Fig.l results in a reduced dark current flow through the photo layer

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28. The rhodium or tin oxide layer 26 becomes a material of the n-conductivity type, while the vitreous alloy layer 28 in the tellurium contacting the layer 26 Surface area consists of p-conductive material. If the Layers 26 and 28 are biased in the reverse direction, for example by connecting the signal electrode layer 26 to a positive voltage source and the photo layer 28 through Electrons that strike their surface facing away from the layer 26 is made negative, the transition between layers 26 and 28 as a barrier to the flow of electrons from layer 28 to layer 26 as long as layer 28 is no-light receives. On the other hand, when the photo layer 28 is exposed, the electron mobility restriction therein becomes Layer increasingly canceled, so that the transition between the two layers no longer acts as a barrier.

A further increase in electron mobility in the Photo layer 28 during exposure is due to the gradual increase in the tellurium content in the direction of the free layer surface after the surface contacting the signal electrode layer 26. Due to the gradual increase in the tellurium content in the layer 28, the formation of transitions or blocking zones in the layer is avoided, which also during exposure the Restrict or prevent electron mobility.

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Due to the absence of such transitions, the photo layer has 28 has a short cooldown so that it is essentially free of Is residual charges that persist from one scan to the next.

When used in the glassy alloy layer 28 arsenic arsenic should be distributed almost evenly over the entire layer. This follows from the fact that the arsenic initially in the vitreous alloy of selenium, tellurium and arsenic used to make layer 28, is evenly distributed. In addition, in the process steps to be described, the boiling point of arsenic is so close in the case of selenium, that both substances evaporate essentially at the same time. At the temperature used for the vapor deposition step the arsenic combines chemically with the selenium to form arsenic triselenide. This form of arsenic, together with its uniform distribution in the glassy photo layer 28, results in a short decay time of the photo layer. ''

During the transition between the signal electrode 26 and the tellurium-rich surface area of the vitreous photo layer 28 serves as a barrier for the current transfer from the layer 28 to the layer 26 i-n of the dark and the dark current to a tolerable level Dimensions [are reduced in the case of the photoconductive storage electrode 29 according to FIG. 2 measures are taken to additionally block this current transition in the dark and thereby

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To reduce the current to an even lower, negligible value, for this purpose a layer jJO can be inserted between the signal electrode layer 2.6 and the glassy photo layer 2δ, which is produced by vapor deposition of a very thin film of a material with a low work function v / ie cerium, cesium or pure selenium on the signal electrode layer 26 can be fabricated. Said materials are "n-conductive" and form a barrier layer with the p-conductive tellurium-rich surface area of the photo layer 28. It has been found that this barrier layer has a stronger blocking effect on the current transfer from the photo layer 28 to the signal electrode layer 26 in the dark than the junction or the barrier layer between the signal electrode 26 and the tellurium-rich surface area of the photo layer 28 according to FIG.

It is not certain whether the cerium or cesium is the barrier substance 30 is present in metallic form after application. True will the cerium or cesium initially applied as a metal, but a certain oxidation or other chemical reaction probably takes place during the subsequent treatment steps, through which at least part of the metal is converted into the oxide and / or selenide form. In the case of the cesium, This probability arises from the fact that cesium is a known active element and willingly with about in the process atmosphere connects oxygen present. In the event of

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Such an oxidation of the cerium probably takes place through it

the crystal reaction of the cerium with the selenium in the layer The layer 30 when formed by applying cerium is, also causes a stabilization of the non-crystalline form of selenium in the layer 28. In the case of the use of

Cerium or cesium is therefore to be assumed that the layer 30 at least partially consists of the oxide and / or the selenide of the The formation of the layer is composed of cesiums or ceriums is. If, consequently, cesium or cerium is used here as a component of the barrier layer 30 di-e, then these are used Equally terms cesium oxide or cerium oxide, Cesium selenide or cerium selenide or a combination of cesium oxide and cesium selenide or cerium oxide and cerium selenide meant.

The barrier layer 30 is so thin that it allows the passage of the Light to the photo layer 28 is essentially not impaired. The thickness of layer 30 is approximately 10 to 50 8. The thickness of the signal electrode layer 26 and the thickness of the glassy photo layer 28 can be the values mentioned in connection with FIG to have.

Fig. 3 shows a photoelectric device, for example a storage electrode 31 * ° ei of the measures for stabilization of the glassy character of the photo layer 2 & are met. Two layers 32 and 3 ^ are provided for this purpose,

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which consist of materials which bring about the desired crystal stabilization of the two surfaces of the vitreous photo layer 28 made of selenium, tellurium and arsenic. If, however, the layers consist of conductor material and the storage electrode 3I is used in an image pickup tube, the layer 34 located next to the electron gun (not shown) should not significantly impair the operation of the tube. "What should be avoided in particular is a loss of resolution in the storage electrode 31 as a result of excessive electrical sideways conductivity of the layer J> h, which would attack or destroy the charge image, which during the optical exposure through the faceplate 16 on the Such a lateral conductivity is not harmful in the other stabilizing layer 32. What is important, however, is that the layer 32 has a sufficiently large electrical conductivity in the direction perpendicular to its surface so that signal charges pass through this layer onto the Signal electrode 26. This also applies to the stabilizing layer 34, since it is desirable that the scanning electrodes impinging on the storage electrode 3I readily pass through the layer.

Suitable materials for the stabilizing layer 32 are for example gold, silver, palladium, germanium and germanium oxide, Gallium, gallium oxide, iridium and antimony. Investigations

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have not produced any evidence that a chemical compound any of these materials is done with the photoconductor. It has been found that of the materials mentioned particularly Gold mechanically stabilizes the crystal activity in the adjacent surface of the glassy alloy layer 28 very well.

The stabilizing layer Jk of the storage | Electrode 31 can be made of a material such as germanium, germanium oxide, antimony trisulfide or antimony trioxide. Of these materials, germanium and germanium oxide are the most suitable. These materials have the required low lateral conductivity and sufficient conductivity in the normal direction for the desired charge transfer.

The thickness of the stabilizing layer 32 can be approximately 6 to 30 8; preferably it is about 6-8. In order to obtain satisfactory results, the thickness of the outer stabilizing layer Jk should be about 10 to 100%. For the thickness of the photo layer 28 and the signal electrode layer 26, the values mentioned in connection with Pig. 1 apply.

It has been found that by applying a stabilizing layer on only one side of the photo layer 28, the thermal Stability, i.e. the stability of the glassy character at a relatively high temperature is greatly improved. In the

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Indeed, in some cases it may be desirable that one surface the photo layer 28 is free of stabilizing material. In order to obtain optimum thermal stability, should however, both surfaces of the photo layer 28 are treated in the aforementioned manner.

4 shows a photoelectric device 35, for example a photocell or a storage electrode, with an electrode layer 26 on a glass substrate 16, a lower stabilizing layer 32, a barrier layer 30 * of a photo layer 28 made of a vitreous alloy of selenium, tellurium and arsenic and an upper one Stabilizing layer Jk. These layers in the arrangement shown in FIG. 4 can have the same composition and thickness as the corresponding layers in the arrangements according to FIGS. 1, 2 and 3.

In the layer arrangement shown in FIG. 4, the barrier layer is located 30 between the stabilizing layer 32 and the photo layer 28. This arrangement of the barrier layer 30 is made up of several Preferable for reasons. One of these reasons is that that formed between the photo layer 28 and the barrier layer 30 Transition the current transmission from the photo layer 28 to the signal electrode 26 blocks more effectively than the transition between the stabilizing layer 32 and the photo layer 28. Another reason is that the barrier layer 30 also has good stabilizing properties has and the glassy character of the photo layer 28 in

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stabilized to a considerable extent. Because of the small thickness of the barrier layer 30, namely approximately 6 to 50 8, the stabilizing layer 32 can exert a considerable additional stabilizing effect on the photo layer 28 through the thin barrier layer. In cases where this cumulative stabilizing effect is not required, the stabilizing layer 32 can be omitted and the required barrier and stabilizing effect. ^T ^ MPACT solely by means of the barrier layer 30 obtained v / ground. Optimal stabilization of the photo layer 2b is, however, achieved when both the barrier layer 30 and the stabilizing layer 32 are present. In this connection it should be noted that the stabilizing layer 32 is also η-conductive, ie the signal electrode layer: 26.

The stabilizing layer jk in the arrangement according to FIG. 4 can also be made so thick that it can serve as a second electrode for a photocell which can expose through the glass substrate 16 by means of a light source. ₍

For the production of photoelectric devices such as photocells or storage electrodes, the various layers of the device can be applied by vapor deposition in successive steps using an apparatus of the type shown in FIGS -, on which several evaporators are arranged (Fig. 6). Around the evaporator ed a tubular evaporation chamber 3-

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•. -16-

made of, for example, corrosion-resistant steel with an upper dome-shaped part 40 with a plurality of openings. One of these openings receives the glass plate 16 to be coated, while other openings receive means for monitoring the thickness of the applied layers. By means of a light source 4l arranged in the chamber J58, a photocell 42 ^ is exposed through the glass plate l6 via a collecting lens 44 made of glass in order to additionally control the thickness of the layers vapor-deposited on the glass plate l6. A bell 45 made of, for example, glass encloses the chamber J5ö and the parts of the device to be described. This bell is evacuated through a pipe socket 46 to a pressure of approximately 2 10 Torr. The chamber 3 & v is kept at the same pressure as the inside of the bell 45-V /itere. "Characteristics of the apparatus are derived from the following description of the individual process steps required for the production of the layer arrangement, for example according to Fig. 4, The maximum number of layers which can be used for the present device is present in FIG.

V. 'if the electrode layer 26 (Fig. 4) consists of rhodium, it can be formed with the aid of the evaporator 47. If an oxide of the tin is not used for the electrode screen, then it can be rr.an this layer before inserting the glass plate l6 into the Place bell 45 on the glass plate. The rhodium evaporator

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47 consists of a rhodium-plated tungsten wire 48. The tungsten wire 48 is mounted on high-current leads 50, which can be connected to a power source, which is a sufficient provides high current to heat the wire 48 to a temperature sufficient to vaporize the rhodium. That Vaporized rhodium condenses not only on the glass plate 16 but also on a monitoring device 51 rait two-spaced Layers 52 and 54 of conductor material on an insulating Pad 56. The conductor layers 52,5 ^ are on a Ohmmeter 58 connected to the resistance of the on the insulating pad 5β vapor-deposited between the two conductor layers Measure rhodium layer. When this resistance reaches about 50,000 ohms, the rhodium layer on the Glass plate l6 a thickness of approximately β 8. The power supply to the Wire 48 is then terminated and the next layer 32, e.g. wise made of gold, is then applied to the rhodium.

The gold layer J2 is applied by vaporizing gold from a gold-plated tungsten wire 60 (FIG. 6) by sending a suitable current through the leads 62 of the wire. A portion of the evaporated gold condenses on the glass plate 1-6 to form a gold layer, while a portion is deposited on a thickness monitor 64 made of quartz. When the monitor indicates that a gold layer approximately 6 8 thick has been deposited, the heating of the wire 60 and hence the evaporation of the gold is terminated.

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The barrier layer 30, if it consists of cesium, can be produced by the spontaneous evaporation of cesium, which is produced by reducing cesium chromate in a bowl or pan 64 which is heated by the supply of electricity via the supply lines 66. Since the thickness of the barrier layer 30 can fluctuate within a relatively wide tolerance range of 10 to 50 S, the thickness of the cesium layer formed over the gold layer 32 on the glass plate 16 is, for example, either by introducing a certain critical initial amount of cesium chromate into the shell 68 or by the Determines the duration of the heating of the shell. It has been found that by completely spontaneous evaporation of approximately 1 milligram of cesium chromate, a cesium barrier layer 30 having a thickness within the specified tolerance range is obtained.

In connection with the production of the vitreous photo layer 28 made of selenium to be applied over the gold layer 32 and tellurium with a graduated tellurium concentration from one side of the layer to the other, and preferably with an arsenic content the problem arises, an even gradation or gradation of the tellurium content. It has been found that such uniform gradation can be obtained by that one has a critical amount of an alloy of 70-82 percent by weight Selenium, 17-29 percent by weight tellurium and 1 percent by weight arsenic in an evaporator dish 68, which is

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'supply is suitably heated via the supply lines 70, wherein then the desired gradation is obtained by fractional evaporation, as it is due to the different boiling temperatures of these materials. In fact, the boiling point of tellurium at atmospheric pressure is 1390 ° C, on the other hand the boiling points of selenium at 688 ° C and arsenic at 61 ° C. In contrast, the relatively low pressures in the present apparatus are the boiling temperatures of selenium and tellurium and arsenic considerably lower, while the ratio of boiling temperatures is the same as at atmospheric pressure,

The introduction of a critical amount of the vitreous alloy into the shell 66 is important in producing the desired tellurium gradation. Bringing initially a relatively large amount of the alloy in the tray 6c and outdoor heated. ^1: -nan the shell to a temperature at which the alloy evaporates **, so da3 is clear first an evaporation product: is formed, the

¹ "" i

is rich in selenium; and verhältnisntässig little or no z ^ v tellurium. There? Arsenic, the boiling point of which is close to that of selenium, is also used in the gen-ii Men /; ο evaporates, which corresponds to its: percentage share in relation to the selenium. It is assumed that at the temperature used the arsenic combines with the selenium to form arsonic selenide.

If, on the other hand, one brings to the Sch "Ie ^ r a relatively low level at the beginning small Meiv: e of the alloy and heated nian sufficiently

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long enough to evaporate all components of the alloy, thus the resulting vapor deposition, which is initially rich in selenium, becomes rich in tellurium. When the in the bowl The amount of alloy introduced is so small that such an extremely thin layer is formed that it is difficult, if not impossible is to separate the selenium-rich parts of the layer from the tellurium-rich parts, then the initial layer behaves practically like a tellurium-rich layer.

By slowly and evenly increasing the amount of alloy A desired uniform gradation of the tellurium content of the photo layer 28 with a tellurium content can be achieved in the shell 68 from about 17-29 weight percent in one surface area to zero in the other surface area.

In order to achieve a desired critical alloy loading of the shell 6fi, a method is used in which alloy pills are added drop by drop into the shell while the temperature of the shell 6c is monitored. For this purpose is used an apparatus of the in Fig. 5 type shown with a rotatable platform or turntable 72 which is mounted on a shaft Jk which passes through a housing fixed to the base 36 bearing 76. The shaft ¹ Jk is coupled to a manually rotatable shaft 78 via a suitable gear drive. The turntable 72 takes a number of pills δθ made of glassy alloy with 70-82 percent by weight selenium, 17-29 percent by weight tellurium and

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1 percent by weight arsenic. To an extremely slow thickening rate To preserve the alloy material, the pills 80 are made relatively small, each weighing about 1 milligram. A tube passed through the wall of the chamber 38 82 extends from the peripheral edge of the turntable 72 to a point perpendicularly above the shell 68. The upper end of the tube 82 is funnel-shaped in order to make it easier for the pills to drip in from the turntable 72. ™

To control the number of pills 80 dropped into tube 82, becomes the upper surface of the turntable 72 of a fixed scraper or doctor arm 84 detected. The scraper arm, under which the turntable can rotate, extends radially via the turntable 72. When turning the turntable counterclockwise, viewed from above in Pig. 5 * are the pills against the outer side or the outer end of the scraper arm 84 is driven. This end corresponds in the radial direction with the funnel end of the tube 82, so that if the pills continue to accumulate at this end, the pills are driven to the circumferential edge of the turntable 72 while placing one or more pills in tube 82 drip or fall. The number of pills drained in this way depends on the speed of rotation of the turntable.

The thermal inertia of the shell 68 is relatively low and allows convenient monitoring of the rate of loading

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delivery of the tray of pills 80. The tray 68 is preferably made of tantalum with a wall thickness of approximately 0.025 0.05 mm (1-2 mils). With such a small wall thickness the shell is sensitive to temperature changes caused by evaporation of the load. To a One or more thermocouples 86 can be attached to the shell 68 to provide a visible indication of these temperature changes be.

When using this apparatus for the production of a photo layer 28 with a uniform gradation of the tellurium content according to an example of the method, the shell 68 is first heated to a temperature of approximately 444-40 ° C. The alloy pills So v / ground initially with such a feed rate dropped into the tray 68, that DLE shell temperature is kept between about 445 and 448 ⁰ C. This relatively slow feed rate is used until the vapor-deposited layer has a thickness of 1/2 micron. This thickness can be determined by measuring the absorption of the light from the lamp 41 by the coated glass plate 16 with the aid of the photocell 42. The light absorption for this relatively small thickness is approximately 40 #. Then the feed rate of the pills is gradually increased, is lowered until the shell temperature to 310 ⁰ C. When this temperature is reached, the thickness of the vapor-deposited layer on the glass plate is approximately 1 1/2 microns, which corresponds to a measured light absorption of approximately 70 #. Then the

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Feed the pills 80 at a rate such that the shell temperature is held at about 510 ° C until the light absorption of the layer reaches a fourth of 88 $, which is a Indicates a thickness of approximately 5 microns.

The diagram according to FIG. 7 shows two function curves X and Y. The light absorption is plotted on the ordinate on a logarithmic scale. The abscissa indicates the thickness in microns. No absolute values of the light absorption are given, since the curves are only intended to illustrate a certain relationship between the photoconductors. In fact, curve X shows the light absorption of a layer in which the tellurium content is uniform throughout the layer, while curve Y shows the light absorption for a photoshift 28 in which the tellurium content is initially relatively high and then in the course of the layering process gradually decreases. The different steepnesses of the curves X and Y reflect the different light absorption properties of selenium ⁽ and tellurium, in that tellurium shows a considerably greater light absorption than selenium.

Point a on curve Y shows that light absorption the layer that results after the first layer portion is evaporated to a thickness of 1/2 micron. At this Layer thickness there is practically no difference between one

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uniform and a graduated tellurium concentration in the layer. If, on the other hand, a layer thickness of 1.5 microns is reached, the above-described method results in a noticeably lower light absorption of the layer, as indicated by point b on curve Y. With a uniform tellurium content, the light absorption corresponding to this layer thickness would be considerably higher, as indicated by curve X. 'In the case of Port below the steam before he gear, the tellurium the Πchic-Vc gradually decreases, as indicated by the upper straight portion of the curve Y is obtained c to the point. At this point the layer thickness has the desired value of 5 microns. While the light absorption at point c on curve Y occurs with a layer thickness of 5 microns, there is essentially the same light absorption in a layer with a uniform tellurium distribution if this layer is very thin, ie only about 2 microns thick. It was determined that the relative proportion of tellurium in material which is vapor-deposited at the starting point of curve Y is approximately 23 percent by weight and that this relative proportion then gradually increases to 0 to approximately 10 percent by weight at point c of curve Y falls off.

The amount of Arren in that used for phcto layer 28 Alloy is so small that its influence on the curves according to Fig.7 is negligible.

The last G'sabilisierschicht 3 4 can - :: they enn germanium

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consists, are produced by vapor deposition of germanium from an evaporator dish 87, which is mounted on supply lines 88, via which the dish 87 is supplied with electricity, which ^{heats it to a temperature of approximately 1050 °} C. sufficient for the evaporation of the germanium (Fig. 6). The evaporated germanium condenses in the same layer thickness on the glass plate 16 and the thickness monitor 64 made of quartz. If the monitor shows a germanium layer thickness of approximately 10-100 8, the ™ heating and thus the coating process is aborted.

After the various layers have been applied in the manner described, the coated glass plate 16 can be inserted into the Tube shown in Fig.l can be installed by melting the indium ring 18 on. Since this is only relatively low Melting temperatures are required, the individual This does not damage any deposits on the glass plate, which has now been assembled to form the faceplate 16.

In cases where the coated storage electrode arrangement according to Pig. 1 is desired and the electrode 26 from an outside The tin oxide produced by the bell requires only a single process step with the apparatus according to FIGS to be made, namely the application of the photo layer 28 with the tellurium graded from one side of the layer to the other

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salary. But you can also use the apparatus for applying the additional layers according to Fig.2-4.

A photo layer made of tellurium / selenium alloy with a graded tellurium concentration and high tellurium content on the side facing the incident light, produced in the manner described, achieves clear advantages over other photo layers. The high tellurium concentration on that surface of the layer on which the incident light strikes first results in a sufficiently high red sensitivity without eliminating those light components which are necessary for the blue sensitivity of the selenium-rich part of the layer. In this way, a panchromatic spectral sensitivity similar to that of the human eye is obtained. The selenium-rich part of the storage electrode thus provides a red, blue and blue-green spectral sensitivity while at the same time maintaining a low dark resistance. Although the conductivity of the layer in the dark tends to increase due to the presence of tellurium in the photo layer, the dark current is reduced by the barrier layer between the photo layer 28 and the layer 26 adjacent in the direction of the incident light an image pickup tube a greater contrast and a better resolution of the image signals. Furthermore, the graded photo layer 26 results in an increased resolution because of the electron

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radiator facing selenium-rich surface area, which is a Low sideways conductivity that destroys the on this Side that could cause layer 2f built-up charge image, has, '.'are in this area noteworthy amounts of Tellurium anvesond, go Would this increase the lateral conductivity and consequently reduces the resolution and contrast of the image signals.

"." As mentioned above, changes in the composition gradient of the layer can be obtained, as indicated, for example, by the curve X in FIG. 7, which shows the light absorption properties for a uniform alloy layer 6 can be produced by, for example, completely avoiding the fractional evaporation of the alloy material by sending the alloy pills to the evaporator with such a rarity that the material evaporates immediately when it is thrown into the shell. else can the entire layer S: with gleichmässiner in 'substantial weight-I prozentualei * composition of selenium and tellurium be st and * ei Ie train is also possible to, vie also described, any change between the graded layer ger. The curve Y according to FIG. 2 and the uniform layer according to the curve X according to FIG in that the R _s' s of the feed the Verdampfr-rschai "e 6S varies with the alloy accordingly.

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One can also only with fractionated vaporization of the alloy material to work by adding a ¹ correspondingly large amount of the alloy in the shell 68 and then heated to vaporization temperature. Under these conditions, selenium and arsenic, as the substances with the lower boiling point, are first evaporated, so that in the

A selenium-rich composition is created in the adjacent area, while the percentage of tellurium increases as the layer continues to build up. Such a photo layer, which is suitable for certain applications, provides a significant blue or blue-green snectral learning sensitivity with an acceptable decay time. For an image pickup tube of the type shown in Plg.l, however, such a layer is not particularly suitable, since the lateral conductivity of the tellurium-rich region of layer 26 would result in poor image resolution and poor contrast.

09818/1374

Claims (1)

Patent claims l.yPhotoelectric device with a conductive electrode and a photo layer applied thereon, thereby characterized in that the photo layer (28) consists of is composed of a mixture of at least two different substances, the weight ratio of these two substances from the layer surface adjoining the conductive electrode in the direction of the other layer surface changes. 2. Photoelectric device according to claim 1, characterized characterized in that the mixture consists essentially of is composed of tellurium and selenium. 3. Photoelectric device according to claim 2, since dur c Ii characterized in that the percentage by weight of the tellurium in the mixture is greatest on the layer surface adjoining the conductive electrode (26) and in the transverse direction decreases evenly through the photo layer to the other layer surface, 4. Photoelectric device according to claim 3 * d a d u r et) characterized in that the conductive electrode (26) or a layer (30; 32) between this and the photo layer $ 00901/1374 (28) is made of n-conductivity type material and adheres to the electrode layer adjacent surface area of the photo layer (28) with the highest percentage of tellurium is of the p-conductivity type. 5. Photoelectric device according to one of claims 2-4, characterized in that on one of the A stabilizing layer (32, 34) for stabilizing the selenium of the photo layer is attached to both surfaces of the photo layer (2δ) is. 6. Photoelectric device according to one of the preceding claims, characterized in that between the conductive electrode (26) and the photo layer (28) a layer (30) made of a material with a low work function is arranged. 7 · Photoelectric device according to one of the preceding Claims, characterized in that the conductive electrode (26) as a transparent layer, the incident Lets light pass through to the photo layer, is formed. 8. Photoelectric device with a conductive electrode surface and a photo layer applied thereon, thereby characterized in that the photo layer consists of an alloy of "selenium, tellurium and arsenic. 009818/1374 £ 9 · Photoelectric device according to Claim 8, characterized in that the alloy from 70-80 percent by weight selenium, 17-29 percent by weight tellurium and approximately 1% by weight arsenic. 10. A method for producing a phato layer from a selan-tellurium alloy, the composition of which changes in the direction from one to the other layer surface, dadu -rch characterized in that successively small amounts of the alloy, with which an evaporator dish is charged, are completely evaporated in such a way that a thin layer with essentially the percentage composition of the alloy is formed on a base; that then the " rate of charging the evaporator dish with the alloy is increased in such a way that the temperature of the evaporator dish decreases uniformly and the percentage of tellurium in the evaporated layer decreases uniformly] and that then the Temperature of the evaporator dish at a lower evaporation temperature is held »in such a way that essentially only selenium is evaporated. 11. The method according to claim 10, characterized in that g e k e η π-seichnet, that the alloy consists of 70-30 percent by weight selenium, 17-29 percent by weight tellurium and about 1 percent by weight Arsenic exists. ■ BhO OFUGSNAL. 009818 / 137.A