DE1564544B2 - PHOTOELECTRIC DEVICE AND METHOD OF MANUFACTURING A PHOTO LAYER FOR IT - Google Patents

Description

The invention relates to a photoelectric device having a conductive electrode and one thereon attached photo layer, which consists essentially of selenium and tellurium.

From US Pat. No. 2,654,853 it is known to use amorphous selenium as the material for the photoconductor layer photocells, image pick-up tubes and other photoelectric devices. Amorphous selenium has the advantage of good sensitivity to blue light, a low one Dark current as well as short response and decay times, d. H. little indolence. Disadvantages of the amorphous Selenium is, among other things, its poor sensitivity in the red spectral range and its instability, which manifests itself in the fact that over time, especially at elevated temperatures, it becomes conductive converts crystalline form. Selenium layers also tend to fatigue, and when exceeded At a certain voltage, reversible local breakdowns occur, through which the dark current is strong is increased.

Attempts have also already been made to improve the sensitivity to red and the stability of photoconductive selenium layers to increase with additives. So is z. B. from the German Auslegeschrift 1039 660 known, Alloy selenium with arsenic. Alloys of selenium with antimony are known from US Pat. No. 3,020,432.

It is also known from the journal "Journal of the American Optical Society", Vol. 42, 1952, p. 221, to use selenium layers for xerographic plates, which by adding about 7% Tellurium and, due to the heating of the substrate, have a higher sensitivity to red than pure selenium. However, it has been found that the resistance of such layers with increasing tellurium content, especially in the range of a tellurium content of 6 to 8%, decreases rapidly.

The present invention is based on the object to provide a photoelectric device whose spectral sensitivity is high and in their characteristics largely correspond to those of the human eye. At the same time aim to indolence small and the stability high.

According to the invention, this object is achieved in a photoelectric device in that the percentage of tellurium in the photo layer on the side adjacent to the conductive electrode is greatest and decreases evenly in the direction through the photo layer to the other side.

Further developments and refinements of the invention are characterized in the subclaims.

In the preferred method of forming a photo layer for the present photoelectric Set up small amounts of a selenium-tellurium alloy, one after the other, with an evaporator dish is charged, so completely evaporated that a thin layer on a base with essentially the percentage composition of the alloy that then the The rate of charging the evaporator dish with the alloy is increased so that the temperature the evaporator dish and thus the percentage of tellurium in the vapor-deposited layer evenly decrease and that then the temperature of the evaporator dish on a lower evaporation temperature is held so that essentially only selenium evaporates.

The advantages achieved by the invention are that you have a photoelectric device receives, in which amorphous selenium, with its inherent good properties, is used as a photoconductor material and the addition of tellurium changes the spectral sensitivity of amorphous selenium is that it largely approximated the panchromatic spectral sensitivity of the human eye is. Furthermore, the photoelectric stand out

ίο facilities 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. It shows

F i g. 1 is a fragmentary view, partially in section, of an image pickup tube having a photoconductive storage electrode according to the invention,

F i g. 2, 3 and 4 are fragmentary sectional views of photoelectric devices, each with one according to the invention Layer of glassy selenium-tellurium alloy,

F i g. FIG. 5 is a schematic illustration of the process used to manufacture the photoelectric devices according to FIG F i g. 1 to 4 usable devices,

F i g. 6 is a plan view of the device according to FIG. 5 in a plane corresponding to lines 6-6 in F i g. 5 and

F i g. 7 is a diagram showing the difference in light absorption between a layer of glassy Selenium-tellurium alloy, in which the tellurium is evenly distributed, and a layer in which the tellurium content decreases, illustrates.

F i g. 1 shows part of an image pick-up tube 10 with a photoconductive device designed according to the invention Storage electrode 12. The tube 10 has an elongated glass bulb 14, which at its one End is closed by a transparent faceplate 16 made of glass, which 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 24. In the other end (not shown) of the piston 14 is the electron beam system for generating the scanning Arranged electron beam. The electron beam is generated by suitable means such as Electromagnetic deflection coils (not shown) arranged outside the piston in a grid pattern the storage electrodes 12 deflected.

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 to 25 Å, so that they are translucent and consequently the light from the object to be recorded is essentially unobstructed by the Layer 26 passes through and reaches the photo layer 28 below. The mentioned layer thickness is also sufficient for the use of the layer 26 as a conductive signal electrode or signal plate.

The photo layer 28 in which the principles of the invention are embodied consists of a glassy one or amorphous alloy of selenium, tellurium and arsenic from about 0.2 to about 0.2 in thickness 5.0 microns. Although the layer works satisfactorily even without arsenic, the presence of

3. . 4th

Arsenic helps to improve the decay properties and the stability of both substances essentially at the same time. With a special exhaust. In the form used for the vapor deposition step, the layer 28 is applied in such a way that the arsenic chemically combines with the selenium to form arsenic triselenide adjacent to the electrode layer 26. This form of the direction of the incident light is rich in tellurium and 5 arsenic, together with its uniform defender relative tellurium portion in the direction of the other development in the glassy photo layer 28, results in a layer side gradually decreasing. For example, a short decay time of the photo layer,
the weight proportion of tellurium in the surface area of the electrode 26 adjoining the signal electrode layer 26 and the tellurium-rich surface area layer 28 is about 23%, while it is used as a barrier for the surface area on the surface of the glassy photo layer 28 on the other side from 0 to un- current transfer from layer 28 to layer 26 is approximately 10%. In such a graduated or darkness and the dark current on a changing photo layer 28, the tolerable percentage can be reduced in the photoconductive composition on the storage electrode 29 according to FIG. 2 surface measures 70 to 80 percent by weight selenium, 15 times taken to block this current transition in the thin 17 to 29 percent by weight tellurium and about 1 gelness in addition, thereby adding up to the thin weight percent arsenic. Good results have been achieved in pushing kelstrom down to an even lower, negligible with about 76 weight percent selenium, 23 weightable value. For this purpose, percent tellurium and 1 percent by weight arsenic can be given a layer 30 of glassy alloy layer 28 in the glassy photo layer 28 between the signal electrode layer 26 and the surface area 20 adjoining the layer 26. If no arsenic is used by vapor deposition of a very thin film, the selenium film made of a material with a low work function can be increased by approximately 1 percent by weight. such as cerium, cesium or pure selenium on the Si-Die arrangement of the two layers 26 and 28 signal electrode layer 26 can be produced. The materials mentioned according to FIG. 1 result in a reduced dark current. 25 are η-conductive and form with flow through the photo layer 28. For the rhodium- the p-conductive tellurium-rich surface area or tin oxide layer 26, a material from the photo layer 28 becomes a barrier layer. Gen-conductive type was used, while the glassy alloy found that this barrier layer had a stronger barrier layer 28 in which the layer 26 had a contacting effect on the current transfer from the photo-layer tellurium-rich surface area of p-conductive 30 28 into the signal electrode layer 26 in the dark. Material consists. If the layers 26 and 28 are biased in unity as the junction or the barrier layer of the reverse direction, for example, between the signal electrode 26 and the tellurdem, the signal electrode layer 26 is connected to a positive, rich surface area of the photo layer 28 voltage source and the photo- according to Fig . 1.

layer 28 by electrons on its surface facing away from the 35 It is not certain whether the cerium or cesium layer 26 hit the surface, nega- the barrier layer 30 is made metallic after application, the transition between the lischer form is present. Although the cerium or layers 26 and 28 as a barrier to the electron cesium is initially applied as metal, it does not flow from layer 28 to layer 26 as long as it is likely to receive no light during the subsequent coating 28. If, on the other hand, a certain oxidation or other photo-layer 28 is exposed, the limiting chemical reaction, through the at least one effect of the electron mobility in this layer of part of the metal in the oxide and / or selenide form, is increasingly canceled, so that the transition between is carried out. In the case of cesium, the two layers no longer see this probability as a barrier from the fact that cesium causes a. 45 is known to be an active element and is ready. A further increase in the electron mobility is connected to the oxygen present in the atmosphere in the photo layer 28 during exposure. In the case of cerium, such a gradual increase in the tellurium content in Rieh oxidation is probably due to the crystal reaction from the free layer surface to that of the cerium with the selenium in layer 28. The signal electrode layer 26 contacting surface 50 layer 30 when it passes through Application of cerium given. The gradual increase in the tellurium level also stabilizes the content in layer 28, the formation of super-non-crystalline form of selenium in layer 28, or blocking zones in the layer avoided, which in the case of using cerium or cesium, the electron mobility is also assumed during exposure, therefore, that the layer 30 can at least restrict or prevent. Due to the cesium 28 used in the formation of the layer, due to the absence of such transitions in part from the oxide and / or the selenide, the photolayer 28 has a short decay time, so that it is essentially composed of cerium. If it is consequently free of residual charges that remain from one scan of cesium or cerium as part of the course to the next. If cesium oxide or cerium is used in the vitreous alloy layer 28, the arsenic should be approximate. monoxide, cesium selenide, or cerium selenide, or some moderately distributed over the entire layer. This combination of cesium oxide and cesium selenide results from the fact that the arsenic is meant in the beginning, or cerium oxide and cerium selenide,
In the vitreous alloy of selenium, tellurium and the barrier layer 30 is so thin that it is essentially evenly distributed through the arsenic, which is used for the production of the layer 28, the light passes to the photo layer 28. Also, is not affected. The thickness of the layer 30 is approximately 10 to 50 Å in the process steps to be described. The thickness of the signal electrolyte point of arsenic is so close to that of selenium, the trode layer 26 and the thickness of the glassy photo-

5 6

layer 28 can be used in connection with FIG. 1, both surfaces of the

have mentioned values. Photo layer 28 treated in the aforementioned manner

F i g. 3 shows a photoelectric device, both.

for example a storage electrode 31, in the case of the dimension- Fig. 4 shows a photoelectric device 35, took, for example, a photocell or a memory photolayer to stabilize the glassy character of FIG 27 are hit. And that are to electrode, with an electrode layer 26 on one two layers 32 and 34 are provided for this purpose, glass carrier 16, a lower stabilizing layer 32, which consist of materials which the desired a barrier layer 30, a photo layer 28 of a Crystal stabilization of the two surfaces of the vitreous alloy of selenium, tellurium and arsenic Photo layer 28 made of selenium, tellurium and arsenic like an upper stabilizing layer 34. This layer causes. If, however, the layers of conductors in the form shown in FIG. The arrangement shown in FIG consist of material and the storage electrode 31 in the same composition and thickness as the enteiner Image pick-up tube is used, the speaking layers should be in the arrangements according to the electron beam (not shown) are initially located - Figs. 1, 2 and 3 have.

The borrowed layer 34 does not denote the operation of the tube. 4 is layer arrangement shown affect significantly. What specifically avoided the barrier layer 30 between the stabilizing layer 32 should be, there is a loss of resolution in and in the photo layer 28. This arrangement of the barrier storage electrode 31 as a result of an excessively high electrical layer 30 is for various reasons pre-transverse conductivity the layer 34 through which the pull. One of those reasons is that between the Charge image would be attacked or destroyed, 20 photo layer 28 and the barrier layer 30 formed that with the optical exposure through the screen transition the current transfer from the photo layer carrier plate 16 on which the jet generator blocks trains 28 to the signal electrode 26 more effectively than the turned side of the photo layer is built up. In the transition between the stabilizing layer 32 and the the other stabilizing layer 32 is such a transverse photo layer 28. Another reason is that the conductivity not harmful. It is important, however, that the barrier layer 30 also has good stabilizing properties the layer 32 has a sufficiently large electrical and the glassy character of the photo layer Conductivity in the direction perpendicular to its upper 28 stabilized to a considerable extent. Because of the area has, so that signal charges wrestle through this layer thickness of the barrier layer 30, namely approximately can be transferred to the signal electrode 26. 6 to 50 Å, the stabilizing layer 32 can through the This also applies to the stabilizing layer 34, since it requires a considerably thin barrier layer through it is that the stabilizing effect exerted on the storage electrode 31 is applied to the photo layer 28 Scanning electrodes easily through the practice. In cases where this cumulative stabilizer layer 34 step through. If the stabilization is not required, the stabilizing layer can be used

Materials 32 suitable for the stabilizing layer 32 are dispensed with and the required barrier and stabilization are, for example, gold, silver, palladium, and germanium oxide, gallium, and gallium oxide can be achieved by means of the barrier layer 30 alone. An optimal stabilization of the photo-iridium and antimony. Investigations have not achieved a layer 28, however, if evidence is provided that both a chemical barrier layer 30 and the stabilizing layer 32 pre-bond any of these materials with them. In this context, photoconductor has to be done. It was found that of the 40 people pay attention that the stabilizing layer 32, like the materials mentioned, especially gold, is η-conductive very well as a signal electrode layer 26.
Crystal growth in the adjacent surface of the stabilizing layer 34 in the arrangement according to the vitreous alloy layer 28 is mechanically prevented. Fig. 4 can also be made so thick that they

The stabilizing layer 34 on the side of the jet generator, which can serve as a second electrode for a photocell,

Storage electrode 31 can be made of a material such as 45 which is passed through glass substrate 16 by means of a light source

Germanium, germanium oxide, antimony trisulfide or through it can be exposed.

Consist of antimony trioxide. Of these materials for the manufacture of photoelectric devices

germanium and germanium oxide are best, like photocells or storage electrodes,

suitable. These materials possess the necessary one can use the various layers of furnishing

low transverse conductivity as well as one for the desired 50 device by vapor deposition in successive

Charge transfer sufficient conductivity in steps by means of an apparatus of that shown in Fig. 5

the normal direction. and 6 attach the type shown. This apparatus has

The thickness of the stabilizing layer 32 can be approximately a base or platform 36 on which several Ver-6 up to 30A; it is preferably arranged undamped (FIG. 6). To the process 6 Ä. In order to achieve satisfactory results, a tubular evaporation stop, the thickness of the outer stabilizing chamber 38 should be made of, for example, corrosion-resistant 34 are approximately 10 to 100 Å. For the thickness steel with an upper dome-shaped part 40 with of the photo layer 28 and the signal electrode layer are arranged a plurality of openings. One of these Open 26 If that is the case in connection with FIG. 1, the glass plate 16 to be coated takes named values in question. 60 on, while other openings facilities for

It has been found that by applying a monitoring of the thickness of the applied layers Include stabilizing layer on only one side of the photo layer. By means of a device located in the chamber 38 their thermal stability, d. H. the stability of the ordered light source 41 becomes a photocell 42 Glassy character at a relatively high temperature through the glass plate 16 via a converging lens 44 temperature, is greatly improved. In fact it can be exposed in 65 glass to the thickness of the on the glass plate In some cases it may be desirable that the one upper vapor-deposited layer is in addition to the control surface the photo layer 28 free of stabilizing material. A bell 45 made of, for example, glass. In order to achieve optimum thermal stability, the chamber 38 as well as the still to be described

equipment parts. This bell is evacuated through a pipe socket 46 to a pressure of approximately 2 x 10 ^-3 Torr. The chamber 38 is kept at the same pressure as the inside of the bell 45. Further features of the apparatus are shown in the following description of the individual process steps which are necessary for the production of the layer arrangement, for example according to FIG. 4 are required. In Fig. 4 is the maximum number of layers that can be used in the present facility.

If the electrode layer 26 (Fig. 4) consists of rhodium, it can with the help of the evaporator 47 are formed. If an oxide of tin is used for the electrode layer, then this layer is applied to the glass plate before the glass plate 16 is introduced into the bell 45. The rhodium vaporizer 47 consists of a rhodium-plated tungsten wire 48. The tungsten wire 48 is mounted on the power supply lines 50, which can be connected to a power source, the one provides sufficient current to keep wire 48 on the

"}. to heat the temperature required for the evaporation of the rhodium. The evaporated rhodium condenses not only on the glass plate 16, but also on a monitoring device 51 with two spaced apart layers 52 and 54 of conductor material on an insulating base 56. The conductor layers 52, 54 are connected to an ohmmeter 58 to measure the resistance of the rhodium layer evaporated on the insulating pad 56 between the two conductor layers. When this resistance reaches a value of about 50,000 ohms, the rhodium layer on the glass plate 16 is about 6 A. Power is then removed to wire 48 and the next layer 32, such as gold, is then deposited over the rhodium.

The gold layer 32 is applied by evaporating gold from a gold-plated Tungsten wire 60 (Fig. 6) by having an appropriate current sent through leads 62 of the wire will. Part of the evaporated gold condenses

Λ on the glass plate 16 with the formation of a gold layer, while part is deposited on a quartz thickness monitor 64. When the supervisor indicates that a gold layer with a thickness of about 6 Å is evaporated, the heating of the wire 60 and thus the vapor deposition of the gold ended.

The barrier layer 30, if it consists of cesium, can by spontaneous evaporation of cesium made by reducing cesium chromate in a bowl or pan 64, the is heated by supplying power via the leads 66 is generated. As the thickness of the barrier layer 30 can fluctuate within a relatively wide tolerance range of 10 to 50 Å, the Thickness of the cesium layer formed over the gold layer 32 on the glass plate 16, e.g. Introducing a certain critical initial amount of cesium chromate into the shell 68 or determined by the duration of the heating of the shell. It has been found that by complete spontaneous evaporation of approximately 1 milligram of cesium chromate provides a cesium barrier layer 30 with a thickness within the specified tolerance range is obtained.

In connection with the production of the vitreous photo layer to be applied over the gold layer 32 28 made of selenium and tellurium with a graduated tellurium concentration from one side to the other the layer and preferably with arsenic content results in the problem of a uniform gradation or to produce a change in the tellurium content. It has been found that such a uniform Gradation can be obtained by

ίο a critical amount of an alloy of 70 to 82 percent by weight selenium, 17 to 29 percent by weight tellurium and 1 percent by weight arsenic in an evaporator dish 68, which is heated by supplying power via the supply lines 70, the desired change then being obtained by fractional evaporation, such as it results from the different boiling temperatures of these materials. Namely are at atmospheric pressure, the boiling point of the tellurium at 1390 ⁰ C, whereas the boiling points of the selenium at 688 ° C and arsenic at 615 ° C. In 'the relatively low pressures in the present apparatus are, however, the boiling temperatures of selenium, tellurium, and Arsenic is considerably lower, while the ratio of boiling temperatures is the same as at atmospheric pressure.

The introduction of a critical amount of the glassy alloy into the shell 68 is necessary for the manufacture of the desired change in tellurium content is important. If you initially bring a relatively large amount of the alloy into the shell 68 and the shell is heated to a temperature at which the alloy evaporates, it is clear that a product of evaporation arises first, which is rich in selenium and contains relatively little or no tellurium. The arsenic, the boiling point of which is close to that of selenium is also evaporated in the amount that corresponds to its percentage corresponds to the selenium. It is assumed that at the temperature used, the arsenic becomes with connects the selenium to arsenic selenide.

If, on the other hand, a relatively small amount of the alloy is initially introduced into the shell 68 and heated long enough to evaporate all the constituents of the alloy, the resulting vapor deposition layer, which is initially rich in selenium, becomes rich in tellurium / If the The amount of alloy introduced into the shell is so small that such an extremely thin layer! If it is formed that it is difficult, if not impossible, to separate the selenium-rich parts of the layer from the tellurium-rich parts, the initial layer behaves practically as a tellurium-rich layer.

By slowly and evenly increasing the amount of alloy in shell 68, one can create a desired uniform change in the tellurium content of the photo layer 28 with a tellurium content of approximately 17 to 29 percent by weight in one surface area to zero in the other surface area reach.

In order to achieve a desired critical alloy loading of the shell 68, one operates a method in which alloy pills are added drop by drop into the shell while keeping the temperature the tray 68 is monitored. An apparatus of the type shown in FIG. 5 shown Art with a rotatable platform or a turntable 72 which is mounted on a shaft 74 which a

109 521/283

9 10

Bearing 76 attached to the base 36 passes through it. The shaft 74 is kept at about 310 ° C via a suitable gear train at a rate such that the shell temperature is maintained until the light is coupled to a manually rotatable shaft 78. The absorption of the layer reaches a value of 88%, turntable 72 takes out a number of pills 80 which indicates a thickness of about 5 microns,
vitreous alloy with 70 to 82 percent by weight 5 The diagram according to FIG. 7 shows two functional selenium, 17 to 29 weight percent tellurium and 1 curves X and Y. The light weight percent arsenic is on the ordinate. Plotted to an extremely slow absorption on a logarithmic scale. The abscissa indicates the thickness in microns. If the pills 80 are made relatively small, no absolute values of the light absorption are given, each weighing approximately 1 milligram. Since the curves are only intended to illustrate a certain relationship through the wall of the chamber 38 between the photoconductors, the tube 82 extends from the peripheral edge of the light turntable 72 through the curve X to a point perpendicular to the absorption a layer is shown in which shell 68. The upper end of the tube 82 is trich- the tellurium content in the common layer is evenly shaped so that the dripping into the 15 is moderate, while curve Y facilitates the light absorption of pills from the turntable 72. for a photo layer 28 in which the

In order that the number of tellurium content dropped into the tube 82 is initially relatively large and to control pills 80, the upper surface of the rotating plate 72 is then gradually reduced by a stationary scraper in the course of the coating process. The different slopes of the scraper arm 84 are recorded. The scraper arm, under 20 of the curves X and Y, give the different light that the turntable can turn past, the absorption properties of selenium and tellurium extend radially over the turntable 72. When turning the again, the tellurium is a considerably larger turntable counterclockwise, seen from above Light absorption shows as the selenium,
In Fig. 5, the pills are against the outer side. The point α on curve Y indicates that light or the outer end of the doctor arm 84 absorption of the layer that results after drifting. This end corresponds in the radial direction of the first layer part with a thickness of Vs microns with the funnel end of the tube 82, so that at is vapor deposited. With this layer thickness there is practically no further agglomeration of the pills at this table between a uniform end of the pills to the peripheral edge of the turntable and a changing tellurium concentration in the 72 and thereby one or more layers. Conversely, if a layer of pills drip or fall into the tube 82. When 1.5 microns are reached, the number of pills drained in this way results in a noticeable speed of the turntable depending on the method described while rotating. lower light absorption of the layer, such as by the

The thermal inertia of the shell 68 is indicated in relation to point b on curve Y. If the tellurium content is uniformly low and allows a convenient, excessive tellurium content, the rate of loading of the tray with corresponding light absorption would be considerably higher than the pills 80. The tray 68 is preferably off, as indicated by curve X. With Fort-Tantalum with a wall thickness of approx. 0.025 up to the step of the vapor deposition process, the tellurium-0.05 mm is manufactured. At such a low concentration layer of the wall gradually decreases as shown by the shell strength is sensitive to temperature indicated 40 the upper straight portion of the curve Y, changes, which is reached c by evaporation of the feed to the point. At this point the has to be evoked. In order to give a visible indication of the layer thickness of the desired value of 5 microns for these temperature changes, one or more thermocouples 86 curve Y at a layer thickness of 5 microns can be attached to while the light absorption at point c on the shell 68. 45 occurs, there is essentially the same light

When using this apparatus for the absorption in a layer with a uniform tellurium position of a photo layer 28 with a uniform distribution, if this layer is very thin, ie only a change in the tellurium content according to a process is approximately 2 microns thick. It has been determined that, for example, the shell 68 is first heated to a temperature of about 444 to 448 ° C, the relative proportion of the tellurium in the material. The alloy 50 starting point of curve Y is evaporated, ungerung pills 80 are initially at such a rate of about 23 percent by weight and that this rela-loading rate is dripped into the tray 68, that the tive portion then gradually to 0 to about tray temperature between about 445 and 10 Weight percent at point c of curve Y is kept from -448 ° C. With this falls proportionally.

slow feed rate is operated as long as 55 The amount of arsenic in the for the photolayer until the vapor-deposited layer has a thickness of 28 alloy used is so small that its one-Va Has micron. This thickness can be determined by the flow on the curves according to FIG. 7 is negligible. be that one can reduce the absorption of the light of the last stabilizing layer 34 when it is off Lamp 41 consists of the coated glass plate 16 with germanium, by vapor deposition of Ger-aid the photocell 42 measures. The light absorption 60 manium made from an evaporator dish 87 for this relatively small thickness, ungeon, which is mounted on leads 88, is about about 40%. Then, the feed rate becomes that which the tray 87 is fed with power Pills gradually increased until the shell temperature they also make one for the evaporation of the germanium has dropped to 310 ° C. When this temperature reaches a sufficient temperature of around 1050 ° C is the thickness of the heat on the glass plate 65 (Fig. 6). The evaporated germanium is condensed Layer about IV2 microns, which siert in the same layer thickness on the glass plate 16 a measured light absorption of approximately 70% and the thickness monitor 64 made of quartz. If the is equivalent to. Then the pills 80 monitor are fed with a germanium layer thickness of approx.

shows about 10 to 100 A, the heating and thus the coating process is terminated.

After the various layers have been applied in the manner described, the coated Glass plate 16 in the in F i g. 1 tube shown can be installed by inserting the indium ring 18 melts. Since only relatively low melting temperatures are required for this, the individual coverings on the glass plate, which has now been assembled to form the faceplate 16, are thereby achieved not damaged.

In cases where the coated storage electrode arrangement according to FIG. 1 is desired and the Electrode 26 consists of an oxide of tin produced outside the bell, needs with the Apparatus according to FIG. 5 and 6 only a single process step to be carried out, namely the application of the photo layer 28 with the tellurium content changing from one side of the layer to the other. However, the apparatus can also be used for applying the additional layers according to FIG. 2

Use. \ to 4.

* By means of a photo layer made of tellurium-selenium alloy with a changing tellurium concentration and high tellurium content on the side facing the incident light, clear advantages over other photo layers are achieved. 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 presence of tellurium in the photo layer tends to increase the conductivity of the layer in the dark, the barrier layer between the photo layer

J layer 28 and the layer 26 adjacent in the direction of the incident light, the dark current is reduced and, when the device is used in an image pickup tube, a greater contrast and better resolution of the image signals are obtained. Furthermore, the above-mentioned photo layer 28 results in increased resolution because of the selenium-rich surface area facing the electron gun, which has a lower transverse conductivity which could destroy the charge image built up on this side of the layer 28. If significant amounts of tellurium were present in this area, this would increase the transverse conductivity and consequently reduce the resolution and the contrast of the image signals.

As mentioned above, changes in the composition of the layer can be obtained, as for example by the curve X in FIG. 7 indicated, which shows the light absorption properties for a uniform alloy layer. Such a layer can be made with the aid of the in FIG. 5 and 6 can be made by, for example, completely avoiding the fractional evaporation of the alloy material by sending the alloy pills to the evaporator at a rate such that the material evaporates instantaneously as it drips into the bowl. In this way, the entire layer 28 can be formed with a substantially uniform weight percentage composition of the selenium and tellurium constituents. Furthermore, as also described, any change between the graded layer according to the curve Y of FIG. 7 and the uniform layer according to curve X according to FIG. 7 obtained by changing the rate of charging of the evaporator dish 68 with the alloy accordingly.

It is also possible to work exclusively with fractional evaporation of the alloy material by a correspondingly large amount of the alloy is placed in the shell 68 and then brought to the evaporation temperature heated. Under these conditions, selenium and arsenic are used as the substances with the lower boiling point evaporated first, so that in the area adjacent to the electrode 26 a Selenium-rich composition arises, while then with the further build-up of the layer the percentage of tellurium increases. Such a photo layer, which is suitable for certain applications, gives a significant blue or Cyan spectral sensitivity with an acceptable decay time. For an image pickup tube from the in Fig. 1, such a layer is not particularly suitable, since the transverse conductivity of the tellurium-rich region of the layer 28 result in poor image resolution and poor contrast would.

Claims (8)

Patent claims: 1. Photoelectric device having a conductive electrode and one attached to it Photo layer, which consists essentially of selenium and tellurium, characterized in that, that the percentage of tellurium in the photo layer (28) on the conductive electrode (26) adjacent side is largest and in the direction through the photolayer to the other Decreases evenly towards the side. 2. Photoelectric device according to claim 1, characterized in that the conductive electrode (26) or a layer (30; 32) between this and the photo layer (28) Material of the n-conductivity type and the surface area adjoining the electrode layer the photo layer (28) with the highest percentage of tellurium is of the p-conductivity type. 3. Photoelectric device according to claim 2, characterized in that on one a stabilizing layer (32, 34) for stabilizing the two surfaces of the photo layer (28) the selenium of the photo layer is attached. 4. Photoelectric device according to one of the preceding claims, characterized in that that between the conductive electrode (26) and the photo layer (28) a layer (30) is arranged from a material with a low work function. 5. Photoelectric device according to one of the preceding claims, characterized in that that the conductive electrode (26) as a transparent layer, the incident light to Photo layer can pass through, is formed. 6. Photoelectric device with a tend electrode surface and a photo layer applied thereon according to one of the preceding Claims, characterized in that the photo layer consists of an alloy of selenium, tellurium and arsenic. 7. Photoelectric device according to claim 6, characterized in that the alloy from 70 to 80 percent by weight selenium, 17 to 29 percent by weight tellurium and approximately 1 percent by weight arsenic. 8. Process for the production of a photo layer from a selenium-tellurium alloy, whose Composition changes in the direction from one to the other layer surface Claim 1, characterized in that according to each other small amounts of the alloy with which an evaporator dish is charged, are completely evaporated, in such a way that on one Put on a thin layer with essentially the percentage composition of the Alloy is formed; that then the rate of charging the evaporator dish with the Alloy is increased in such a way that the temperature of the evaporator tray and thus the percentage Share of tellurium in the vapor-deposited layer evenly decrease and that then the The temperature of the evaporator dish is kept at a lower evaporation temperature so that essentially only selenium is evaporated. 1 sheet of drawings