DE2458367A1 - PHOTOCONDUCTOR IMAGE RECORDING DEVICE - Google Patents

Description

RCA 65789 December 9, 1974

üS Ser.No. 423,454 ⁷⁷⁶⁰ " ^{74 Dr} ' ^v

Filing Date: December 10, 1973

RCA Corporation

New York N.Y. (V.St.A.)

Photoconductor imaging device

The present invention relates to a photoconductive image pickup device such as a Target or storage plate of a vidicon image pickup tube, or an electrophotographic plate, with a body of photoconductive semiconductor material, one of two opposing surfaces of which is about 100 to 1000 A * thick layer of solid insulating material adjoins, and with a contact arrangement, by means of which an electrical voltage can be applied to the semiconductor body and the layer Charge carriers corresponding to a radiation energy distribution of an image falling on the layer through the body lets flow.

The target or disk of a vidicon image pickup tube usually contains a photoconductive body, one side of which is provided with a light distribution is applied while the opposite side is scanned by an electron beam. In the construction it is such a storage disk, especially if the Photoconductive body made of a semiconductor material, important to ensure that the scanning electron beam makes a blocking contact with the semiconductor body, i. e.

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that he does not penetrate into this'. At the same time they have to Holes or holes in the photoconductor body generated by the striking light distribution, the Leaving photoconductive body on the scanned side and combining it with electrons from the scanning beam can be neutralized ..

Usually the required barrier layer is either made up of a material with a high discharge potential the scanned side of the photoconductor body, which is a Schottky surface barrier layer forms, or through a p-conductive zone on the scanned surface of the then η-conductive photoconductor body, which forms a pn barrier layer on the scanned surface. In both cases, however, the Transverse conductivity on the surface of the photoconductor body too large to allow the charge distribution corresponding to the light distribution to be able to maintain and the surface must therefore in an arrangement of discrete barrier layers be divided to ensure the required sheet resistance. Such textured surfaces are, however expensive to manufacture and relatively prone to failure.

There are also image pickup tubes known that unstructured storage disks with insulating layers and photoconductive Contain semiconductor bodies, e.g. made of CdSe Manufacture of these known image pickup tubes is, however complicated and expensive if they meet higher requirements, e.g. have to have a low dark current.

The photoconductor plate of an electrophotographic

phical device is similar to the storage disk of an image pickup tube and therefore has similar problems.

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The present invention is based on the object of avoiding the deficiencies outlined above.

This task is done by one with photo conduction working, image-taking device released, which has a body made of photoconductive semiconductor material and a Contains layer of a solid insulating material, which is arranged on one of the two sides of the semiconductor body. According to the invention, the insulating material is of the type which has movable, deep-lying charge carriers and forms a blocking contact with the semiconductor body.

In the following, embodiments of

Invention explained in more detail with reference to the drawing; show it:

Fig. 1 is a sectional view of an embodiment of a photoconductive working, with a Image to be acted upon device according to the invention;

Fig. 2 is a sectional view of a vidicon image pickup tube; which contains the device according to FIG. 1 as a storage disk and

Figure 3 is an energy diagram for a device according to the invention which includes a cermet insulating layer.

1 shows an exemplary embodiment of an image recording device 10 operating with photoconductivity, one of which is essentially flat and exposed to light during operation Body 12 made of a photoconductive semiconductor material, such as silicon, gallium arsenide, gallium phosphide, Contains cadmium selenide, cadmium telluride, etc. The body 12 has opposing surfaces or sides 14 and 16. Which photoconductor material is used in particular,

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-A-

depends on the wavelength of the perceptible through the photoconductor Radiation. The semiconductor body 12 has

16 preferably a carrier density of at most about 17 electrons / cm and a thickness between 1 and 20 µm. The thickness and the carrier density of the semiconductor body 12 should be selected in this way that the semiconductor body is practically completely in the case of the voltage applied to it during operation of the device 10 is impoverished in charge carriers. On the surface of the body 12 there is a layer 18 made of a transparent, electrically conductive material, e.g. a metal or tin oxide.

On the surface 16 of the body 12 made of semiconductor material is a layer 20 of a solid insulating material with a thickness between about 100 8 and 1000 8. The material of the layer 20 has a high density of "deep" charge carriers (ie from about 10 to about 10 carriers / cm), which are essentially at the Fermi level or "further away" from the associated energy band in which the conduction takes place, i.e. the valence or conduction band, as will be explained further below. The mobility of these carriers is small, ie about 10 ~ ⁶ to about 10 " ¹² cm ² / Vs, so that the layer material can be referred to as an insulator or almost as an insulator. The specific resistance of the material

1 2 rials of layer 20 must be greater than about 10 ohms per square

drat and less than about 10 ohms per square. In contrast in addition, the movable carriers in conventional insulating materials have densities of less than 10 per cubic centimeter and

typical mobility between 1 and 10 cm / Vs. The material of the layer 20 must also have a blocking contact can form with the semiconductor body 12.

The layer 20 is preferably made of a material in the form of a system of particulate! metal

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and insulating material, i.e. a mixture or combination an insulating material with substantially uniformly dispersing roughly granular metal particles. The density of the metal particles in a special insulating material becomes chosen according to the desired values of carrier density, carrier mobility and sheet resistance. For layer 20, metal-insulating material dispersions known as cermets are particularly preferred made up of small particles of electrically conductive metal contained in a matrix of glass or other ceramic-like material are dispersed.

Suitable metal-ceramic dispersions (cermets) can be produced by simultaneous deposition, e.g. by cathode sputtering or vacuum evaporation of a conductive metal such as gold, silver, copper, tungsten, aluminum and The like., and an insulating material such as silicon dioxide and Alumina can be produced. Mixtures of metal particles and glass frit or other glass solder are also suitable or fusion glass materials applied to and fused onto the semiconductor body 12. In the case of materials of the last-mentioned type, each metal particle acts like a single charge carrier. Generally you can electrically conductive particles, such as metal particles of a cermet, in a suitable ratio with a sealing or fusing glass (sealing-glass) to be mixed according to the Fusing or baking to give a desired carrier density and resistivity.

Other fixed values can also be used for layer 20. Insulator-like materials are used that have the required specific resistance, the required carrier concentration and the ability to form a blocking contact with the semiconductor body 12. Layer 20

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-S-

can for example consist of a material composition that contains an electronically conductive glass, such as ^ν o ⁰ 5 ~ ^Ρ 2 ° 5 ° ^ ^{er V} 2 ° 5 ~ ^K 2 ^PO 3 ° ^ ^{er e} ^ ⁿ equivalent vanadium oxide phosphate glass. Such materials have deep charge carriers at or near (ie substantially at) the Fermi level and the ability to form a blocking contact with the semiconductor body 12. Alternatively, ion-conducting solids can also be used with advantage which have deep supports at or in the vicinity of the valence band, since these are generally also able to form a blocking contact with an n-conducting semiconductor material. On the other hand, solids with ionic conductivity, which have deep supports at or in the vicinity of the conduction band, can advantageously be used in order to form a tearing contact with a p-conducting semiconductor material.

Fig. 2 shows a vidicon image pickup tube 22 which is a photoconductive image pickup device contains. Otherwise, the structure of the image pickup tube 22 is conventional, it has an elongated piston 24 on which at one end there is a transparent front panel 26. The semiconductor body 12 of the photoconductive image pickup device 10 in the image pickup tube according to FIG. 2 is preferably made of an η-conductive semiconductor material. The piston contains an electron gun Scanning arrangement 28, which can be constructed in a conventional manner. The photoconductive device 10 is like one Ordinary storage plate of an image pickup tube arranged in the piston 24 on the inside of the front plate 26. The distraction the abta ± ending electron beam can be done with the help of magnetic coils, not shown, which are outside of the Pistons 24 are arranged. As FIG. 2 shows, the device 10 is arranged in the piston 24 so that the conductive layer 18 touches the inside of the front plate 26, while the layer 20 of insulating material of the electron gun

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and scanning assembly 28 faces. The conductive layer 18 is made of a translucent, electrically conductive material such as tin oxide.

The image pickup tube 22 can be operated with

Voltages are fed, as is the case with the known Vidicon image pickup tube is common. The assembly 28, which is an electron gun With electrostatic deflector, the surface of the insulating material probes existing layer 20 of the device 10 working as a storage disk or target with an electron ' radiate. The electrons of the electron beam are "thermalized" by the layer 20 of insulating material, in which the electrons get trapped in the low-lying levels. For example, if the material of the layer 20 consists of a Cermet material or an electron-conducting glass, the electrons are captured near the Fermi level, as shown in the energy diagram of FIG. 3. On the other hand, if the material of layer .20 is ion-conductive Glass with deep supports in the vicinity of the valence band is (where the semiconductor body 12 is assumed to be η-conductive becomes) the electrons are trapped in low-lying energy levels near the valence band. This thermalization of electrons in deep-lying carrier levels has the consequence that charge carriers are at the interface between the layer 20 and the semiconductor body 12 accumulate, since, as mentioned, the deep-lying carriers of the material of the layer 20 have a certain mobility in the layer. The high specific resistance of the insulating material However, the layer limits the migration of electrons in the lateral direction along the interface, so that can build up an electrical charge pattern in this interface.

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The radiation distribution representing the image of a scene to be recorded falls through the front plate 26 and the transparent conductive layer 18 and generates 12 electron-hole carrier pairs in the semiconductor body in accordance with FIG Intensity distribution of the light radiation from the scene to be recorded. The holes migrate as in the diagram of FIG. 3 is shown through the semiconductor body 12 and recombine with the electrons that are at the interface between the semiconductor body 12 and the insulating material layer 20 have accumulated, so that the electrical Charge in this interface is reduced in accordance with the intensity distribution in the image of the scene to be recorded. The electrons generated by the action of light become an output line through the transparent conductive layer 18 30 and then fed to a fixed voltage source. In this way, there will be a residual charge distribution on a part of the layer 20 adjoining the semiconductor body 12 at the interface between the semiconductor body 12 and the layer 20 generated. In general, the intensity of the charge distribution along the layer changes and adjusts according to the intensity distribution in the image of the scene to be recorded This scene represents the corresponding charge image. By thermal emission of electrons from the gaseous, somewhat conductive Layer 20 in semiconductor body 12 creates a dark current.

In the photoconductive one serving as a storage disk Device 10, the layer 20 made of insulating material is used to remove the electrons from the scanning electron beam to collect and to prevent the electrons from the scanning electron beam from entering the semiconductor body 12 to flow, i.e. to form a blocking contact, just like a metal layer or a pn junction. In the interface between the layer 20 and the semiconductor body 12 is thus generated by the carrier generated by the radiation, the

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with electrons, which are accumulated at this interface have, recombine, created a pattern from the remaining charges. The high specific resistance of the insulating material the layer 20 largely prevents a lateral discharge of charges at the interface, see above that the charge intensity distribution is essentially maintained and there is no need for the Structure layer 20 or break it up into an array of individual blocking contacts, as is commonly done at Image recording arrangements are the case in which a metal layer or a pn junction to form a blocking Contact with a photoconductive semiconductor is used. For this reason and because the layer 20 is made of insulating material a blocking contact with the semiconductor body 12 analogously forming a pn junction is established in the course of For periods of less than about 0.1 seconds, charge loss at the interface is substantially avoided.

The photoconductive image pickup device 10 can also be used as a plate for an electrophotographic Facility to be used. In such an application, a charge or an electrical potential, which can be either negative or positive, applied to layer 20 (in its thickness direction). This can done by bringing a metal electrode into contact with the surface of layer 20 and between this electrode and the semiconductor body 12 applies a bias voltage. The electrons or holes (depending on the sign or the polarity of the surface charge desired at the interface between layer 20 and body 12) Those who enter the layer are trapped in it and, because of the blocking transition, collect at the Interface between the layer 20 and the semiconductor body 12 in this interface.

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The body 12 is then presented with a photograph

of a scene to be recorded, e.g. a printed page, exposed. The light image can either through the layer 20 (if this is sufficiently transparent) or the transparent Electrode 18 drop and then penetrate into the semiconductor body 12 in order to there electron-hole carrier pairs produce. The charge carriers created by the photogeneration migrate to the interface between the semiconductor body 12 and the layer 20 to recombine there with the accumulated carriers. If layer 20 is negative is charged, the holes created by the photoelectric effect migrate to the interface, while when positively charged Layer 20, the electrons generated by the light migrate to the interface. Finally, it remains on layer 20 a distribution from the rest of the accumulated charge carriers that form a charge image corresponding to the image to be captured Scene represents.

A source of toner particles is then passed over layer 20. The toner particles are made by those Areas of the layer 20 are attracted which contain charge carriers, so that a toner image is formed on the layer 20. The toner image is then transferred to a permanent carrier, such as a sheet of paper, and there, for example by heating fixed.

In an electrophotographic facility Thus, the layer 20 of the photoconductive device 10 serves to collect the charge carriers in it and prevent them from flowing away to block the charge carriers in the semiconductor body 12. The distribution of the carriers corresponds to the light distribution of the scene or original to be recorded or copied. The high specific resistance of the layer 20 prevents lateral drainage of the carrier and it forms

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therefore, a toner pattern corresponding to the image to be photographed Scene or the original image to be copied.

The term "deep-seated" girders is used here

Carriers with an energy level - mean that essentially is at the Fermi level or an energy level that is from the energy band which is responsible for the conduction of carriers of polarity the surface charge that accumulates at the interface between the semiconductor body 12 and the layer 20 is responsible (i.e. the valence band for hole or hole conduction or the conduction band for electron conduction) is "further away" than the Fermi level (i.e. in the energy band diagram "above" or "below" the Fermi level lies). If, for example, holes are to accumulate at the interface and if an ion-conducting layer is to be used for layer 20 If glass is used, the deep supports must be in the Energy band diagram "above" the Fermi level and further away from the valence band, which is the one responsible for conducting holes Energy band is located. In order to ensure a blocking contact with the semiconductor body 12 and a Conducting charged carriers through the photoconductive device 10 should be prevented by the deep-seated girders This material can be chosen so that it is sufficiently far from the one responsible for the polarity of the surface charge Conduction tape are removed to give the desired blocking contact.

The present photoconductive image pickup device 10 differs from the known HalHeiter image pickup devices, which contain an insulating layer on a semiconductor body, in several ways. There the device described here operates with an insulating layer 20 containing movable, deep-lying supports, such as was defined above, one does not particularly need in particular

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to apply high voltages to the layer 20 to reduce the voltage applied to the surface of this layer through the layer and to the interface between body 12 and layer 20. In fact, at an insulating layer thickness of 1000 8, a voltage of less than 1 volt is generally sufficient to ensure a satisfactory imaging or image recording operation of the device 10, without affecting the dark current behavior. The material of the layer 20 then enables the surface charge to be neutralized by photo-generated carriers without any appreciable voltages or fields being applied to this layer to need. In contrast, devices with a conventional insulating layer without moving, deep-seated Carriers work, higher voltages above 5 volts are necessary. In these known image recording devices The high voltages and voltages required for neutralization of the surface charge by the photogenerated carriers tend to occur Fields to negate the ability of these bodies to prevent surface charges from penetrating the corresponding ones To prevent conduction-bearing strips of the semiconductor body, whereby the dark current of the device increases and other disturbing Effects such as afterimages occur as a result of the persistence of charge distributions created by previous images became.

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Claims (5)

Claims Photoconductive, image-receiving device with a body made of photoconductive semiconductor material, its one of two opposite surfaces to an approximately 100 to 1000 8 thick layer of solid ■ Insulating material adjoins, and with a contact arrangement, by means of which to the semiconductor body and the layer one electrical voltage can be applied, the charge carriers corresponding to a radiation energy distribution falling on the layer allows an image to flow through the body, characterized in that the insulating 14 19 material contains about 10 to about 10 deep-lying charge carriers per cubic centimeter, which are located essentially at the Fermi level or further away from the energy band responsible for the conduction of carriers of the respective polarity; that the mobility of the carrier is about 10 " ⁶ to about 10 ~ ¹² cm ² / volt / s; that the layer (20) of insulating material forms a blocking contact with the body (12) consisting of semiconductor material, so that charge carriers at one the part of the body adjacent to the layer can be accumulated as an image of the radiation energy distribution; and that the insulating material has a specific resistance in the direction or plane of the layer (Sheet resistance) from about 10 ohms per square to about 10 ohms per square, so that the intensity changes of the accumulated charge can be substantially maintained for a period of time greater than about 0.1 seconds. '50982 A / 0720 2. Ehrrichtung according to claim 1, characterized characterized in that the contact arrangement has an electrically conductive layer (18) on the other of the two opposite surfaces (14, 16) of the body (12). 3. Device according to claim 1, characterized in that the layer (20) consists of the solid insulating material contains a conductive glass. 4. Device according to claim 1, characterized in that the layer (20) consists of the solid insulating material contains an ion-conducting glass. 5. Device according to claim 1, characterized in that the layer (20) from the solid insulating material contains an insulating material in the particles of an electrically conductive Material are dispersed. 6. Device according to claim 5, characterized in that the layer (20) consists of the solid insulating material consists of a cermet material. 7. Device according to one of the preceding claims, characterized by the Use as a storage disk for an image recording or camera tube. 8. Device according to one of claims 1 to 6, characterized by the use as an electrophotographic plate in an electrophotographic or xerographic machine. 5 09824/0720