DE1621328A1 - Process for the production of a vitreous semiconductor and semiconductor element produced by the process - Google Patents

Description

Dipl.-Ing. F.Weickmann, Dr. Ing.A-Weickmann, Dipping. H. Weickmann D1PL.-PHYS. Dr. K. Fincke patent attorneys

8 MUNICH 27, möhlstkasse 22, phone number «3921/22

j-—

IDBM

■ RANK ZEROZ LIMITED, Rank Xerox House "338" Euston Road, London N.W · 1 »England

Process for producing a vitreous semiconductor and semiconductor element produced by the process

The invention relates to semiconductors or semi-insulators and in particular to a method and method for manufacturing new vitreous semiconductors Elements using semiconductors.

Two common semiconductors are highly purified Silicon and germanium with small traces (parts per million or billion) of selected impurities and / or crystal defects which affect the semiconductor properties change. . '""

These impurities either cause loosely bound electrons that move and therefore carry a current

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can or take away electrons from their normal lattice location, so that a "hole" is formed that a plectrum with a neighboring beard picks up; the movement of this electron creates a new hole »which in turn is reoccupied. The resulting movement of the hole is equivalent to an electrical conduction in a direction which is opposite to that of the slectron movement. Some of the more important semiconductor materials are silicon, germanium, selenium, copper · \ oxide (Cu ₉ O), Bleiüulfid, SiIiziumcarbid, lead telluride, and other compounds. Typical semiconductor applications are rectifiers, modulators, detectors, thermistors, photocells, transistors and electrical circuits.

As can be seen from the explanations above, semiconductors can consist of individual elements or of various compounds with semiconducting properties exist.

In the manufacture of known semiconductor materials

if necessary »precisely controlled process steps, such as special melting techniques to be used in crystal growth, epitaxial growth, doping techniques, etc. Such carefully controlled Processes add to the cost of the final product. It exists hence an ever-present demand for new semiconductor materials, which have a wider range of desirable electrical properties and yet are simply economical can be produced.

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L-er ν er lying enlirfindung is based on the task of a to specify a new class of semiconductors »which do not have the disadvantages mentioned above.

Another object of the invention is to provide a method for To specify the production of thin layers of materials with the desired electrical properties an improved system for producing thin layers of material with improved electrical properties can be provided.

In particular, the invention is also concerned with a new one Class of vitreous semiconductors desired photoconductive and improved electrical properties.

In a method for producing a vitreous semiconductor according to the invention, it is provided that simultaneously a metal and a non-metal are heated to form vapors of these components, causing the vapors to become a substrate transported »and that the vapors are deposited on the substrate in the form of a glass-like semiconductor film.

üin semiconductor element manufactured according to the aforementioned method is through a thin layer of a vitreous semiconductor »the at least one metal and at least one at Non-metal solid at room temperature contains »marked.

With the method according to the invention, new types of glass are created Ha Lbloiter with a wide area from together,

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, Settlement by simultaneous evaporation of at least a metal and at least one non-metal created on a substrate. By separating the vapors from the components a substrate, the various atoms are randomly mixed to form a continuous, homogeneous, non-crystalline film on the substrate. These films can be made in any suitable thickness, although thicknesses of a few hundred angstroms can be made For example, films from about 1000 angstroms up to 200 microns and higher are more suitable for semiconductor applications.

The materials of the invention can best be considered vitreous Semiconductors or semi-insulators. These materials have electrical properties, which differ from those of the individual components or from compounds in a stoichiometric distribution. X-ray diffraction grid these materials are of so-called. vitreous or non-crystalline type. These vitreous Semiconductors can be described as thermodynamically metastable, although they have a high degree of phenomenological Have stability and maintain their structure at relatively high temperatures. In some cases this is the crystallization temperature this vitreous semiconductor is higher uls that of the individual components alone

The new class of semiconductors includes elements which are selected from at least one solid or liquid metal and at least one solid non-metal.

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Typical metals are cadmium, zinc, gallium »lead, tahllium, · Neodymium, mercury, copper, silver, manganese, aluminum, indium and j / ismuth. Typical non-metals are selenium, boron, arsenic, Carbon, phosphorus and sulfur.

Further details and advantages of the invention emerge from the following description with reference to the figure.

The figure shows an embodiment of a device for Manufacture of thin films of vitreous semiconductors.

In the device shown in the figure, a bell 10 sits on a bearing plate 11 which has vacuum lines 12 and Hegel valves 13. ^{Resistance heating circuits I 1} +, 15 are provided for heating evaporation crucibles 16, 17 containing evaporation samples 18, 19. On a holder containing a water-cooled base 21

20, a water cooling device 22 is seen from above. A substrate 23 to be coated is held by the water-cooled base

21 supported. An aluminum mask 2k hinged to the base 21 serves to rest on the substrate 23 in order to cover the substrate until the evaporation samples 18 and 19 are heated to a suitable temperature.

The metal and the non-metal are each in a separate one inert crucible, for example made of quartz or hard glass, introduced. When regulating the evaporation of the Components, it is desirable to keep the temperature of the compo-

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nents between your setaelzpiuuiktt you keep your boiling point. " During the production toeispislsifleise an amorphous cadmium-selenium film with efcwa 20 J TCadmiaim and about 80 55 selenium, a temperature was obtained efcsaa 217 ⁰ C for. the gel and about 322 ⁰ C for the Caümtom. found to divide anisice. Zulp increase in selenium in the fiIa wItu 'you' temperature of the selenium container increases and / or the temperature of the Eadmiöm container is lowered. Ziar Erlniölhiiainii; d @ ip ladmiöMaenge im P vjerden the aforementioned TejEpe ^ afrflirainiflenimgen imigskeh Is a very slow one. Yerdaaffliframgs intended, so the evaporation temperature is a © "! © a? toeider components kept at a temperature below egg selhaelapraiikte-

The vacuum chamber "is held aaif a Ifäkmm ? On ^ twa 2ylö ^J Ms 2x10" Torr »otoolhl siin Yakaajiii above or below this area elbeaaf al Iss ^ aeidens can be used for dividing. With (the © iteaa gemairaiEitea conditions tvi-ieü a film thickness of about S toi® JQ MitoriDai eriaalten, i / jeno. Dis evaporation for a time waa efaaa 1 Ms 3 hours, at a vacuum of about 2x10 Τοιργ äairclhgel'fflhii't; naird · Obviously, the amount of an ibestiimteEL Kwrngmmnt® in the crystal clear film primarily depends on the hanging · des
metals from »vjelche at one
is dependent. Be it
by steam transport or
conditions can be formed

Metal or Draiek's tempera kwc ~ © in glass-like film also * äe under N

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The glassy semiconductor films can be on any one conductive or insulating suitable substrate. Typical conductive substrates are made of brass, Aluminum, stainless steel »conductive coated glass or plastic, etc. Typical .Isolators are quartz, hard glass, ■ jlimer, polyethylene »etc. In some cases it may be desirable seä-n to completely eliminate the substrate.

Semiconductor ade compounds are generally composed of combinations of a metal and a non-metal. When defining the boundary between metals and non-metals, a line known as the Zintl boundary, drawn diagonally through the periodic table, serves to separate the metals from the non-metals are characterized in that they cannot be stoichiometric. Although crystalline compound semiconductors can deviate slightly from the stoichiometry, the vitreous materials according to the invention can be produced without taking the stoichiometry into account. In the case of the vitreous materials according to the invention, very wide deviations from the stoichiometry of corresponding crystalline compounds are the general rule and stoichiometric combinations are only a special case.

The structure of the materials according to the invention is glass-like and! - 'non-crystalline. The structure is

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The essence of an intermediate or long-range-order phase. X-ray diffraction grids are of the so-called vitreous or non-crystalline type. These compounds cannot normally be made into glasses (melt cooled) and vitreous materials or glasses are not known to have ever been made in these systems. However, it has already been described that attempts to produce these materials have been unsuccessful. Specifically, in "The Structure of Glass", Vol.2, page ¹ IlO ₁ by Kolomietes et al, Consultant's Bureau, New York (1960) described that glasses cannot be obtained if copper, silver, gold ₈ zinc, cadmium, mercury, gallium, indium, thallium, germanium, tin or lead together with selenium, sulfur or arsenic are ^{heated to 900 °} C. and then evaporated.

With regard to their electrical properties, the glass-like materials according to the invention semiconductors or semi-insulators, i.e. they have a valence and conduction band, which are separated by a forbidden zone. Their electronic properties are different from those of the components alone or a stoichiometric crystalline compound these components different · Although they are considered thermodynamic can be termed metastable »they have and retain a high degree of phenomenological stability their structure even at temperatures above the

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Room tempera tar lying. Your crystallization temperature is in some cases higher than the utilization temperature dsr individual components.

not these glass-like materials can / by any melting technique, but only by evaporation from the Vapor phase can be obtained. In fact, these materials are in a liquid state to above the boiling point of one of the components also immiscible. Glass-like systems with a metal content of up to 30 atoms were obtained without this Cool the substrate below room temperature.

In a typical embodiment of the invention the non-metal selenium and a group of metals which from cadmium, zinc, · gallium, lead »thallium, indium and wisiaite consists, a group of vitreous semiconductors that are specifically applicable in xerography »These components show a pohto-conducting spectral behavior in the wavelength range from visible light, up to and including infrared »light. The above metals form in combination with Selenium vitreous semiconductor, which is an electrostatic Can absorb charge and when irradiated with light & Ln create an electrostatic latent image. This BiIcS can be developed in a known xerographic manner, as shown, for example, in U.S. Patent 2,297,691 is described.

This by simultaneous pre-dipping of bismuth and selenium

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material obtained is sensitive to infrared radiation and can therefore be used in a xerographic system which emits radiation outside the visible spectrum used. In addition, bismuth with selenium can also be used in non-xerographic systems; with such '' Systems are / are infrared photodetectors, vidicons, Light intensifying panels, electroluminescent and others electro-optical arrangements «

When used in xerography, the above-mentioned materials are evaporated onto a suitable conductive substrate such as brass * aluminum, stainless steel, conductive coated glass or plastic, etc. A uniform electrostatic charge is generated on the xerographic plate thus produced by means of a corona charge in order to sensitize its entire surface. The plate is then placed on an image of activating electromagnetic radiation, for example light, which effectively balances the charge in the exposed areas of the photoconductor, while a latent electrostatic image remains in the unexposed areas. Dax image can be transferred or transmitted to another material, wherein the development is carried out by applying finely divided electrostatic mark particles on the surface of the \ photoconductive material to said image to make it clear. It should be noted that any suitable method "may be used" to generate an electrostatic

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Image. Typical possible techniques consist in the use of a pen matrix in the form of a pen head « & tiftröhren, etc.

In a further embodiment of the invention it is possible to control the degree of order present. Under certain conditions, a second phase of either crystalline, intermediate or long range order can be obtained which is dispersed through the vitreous non-crystalline matrix. This can be achieved firstly by controlling the relative amounts of the two components to be evaporated, secondly by controlling the substrate temperature, and thirdly by subsequent heat treatment. Such two-phase dispersions are also uniform in that they are mixed in the vapor state on an atomic scale. Precipitated second phase in the oxide "£, ^l: lsem are known $ these are, for example," Pyroceram "and heliochromisch.es (Photocromic) Glass j This however are ordinary Oxydgläser which can be prepared from the melt.

In the embodiment in question, the second intermediate or long-range order phase dispersed in the vitreous non-crystalline matrix are obtained, by merely raising the temperature of one of the components to be evaporated to a relatively higher amount than the temperature the other component is increased * For example, a läimiumselenfilin, the selenium is produced on a

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Maintained evaporation temperature of 217 ° C and the evaporation temperature of the cadmium increased to about 375 ° C (compared to a normal evaporation temperature of about 322 ⁰ C). Increasing the evaporation temperature results in the formation of about 30 % of an intermediate or long-range ordered crystalline phase which is dispersed in a vitreous matrix of cadmium and selenium.

Such glassy semiconductors have the same scope "by using semiconductors and semi-insulators \ i or the are. They are - as photoconductors, luminous materials, electroluminescent materials, circuit arrangements, »subconductors,» thermoelectric materials, »ferroelectric materials,» magnetic materials, »electrophotographic receivers,» etc. » usable. The following examples show specific embodiments of the production process according to the invention and the use of vitreous semiconductors. The parts and percentages are "parts by weight" and percentages by weight, unless otherwise stated. The following examples set forth various preferred embodiments of the invention.

Example I.

A 7 micron thick film containing approximately 20 % cadmium and 80 % selenium is produced on a NESA hat by placing 10 gram samples of cadmium and selenium spherical oaks in separate crucibles. The quartz crucibles are placed in a vacuum chamber which is set to a vacuum of about 2x10 ^y Torr

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is evacuated. A NESA glass substrate is placed on a "water-cooled base, which is located about 30 _% hQ cm (12 in) above the quartz crucibles and is maintained at a temperature of about ⁴ h 0 C. The NE3A glass is made with masked by a thin aluminum plate, which is removed when the cadmium and selenium crucibles have reached the evaporation temperature. The cadmium and selenium are then evaporated onto the WESΑ substrate, the temperature of the cadmium crucible being raised to about 322 ⁰ C and the "

ο ^{w the} temperature of the selenium crucible is kept at about 217 "" These conditions are maintained for about 2 1/2 hours, after which the evaporation is stopped. "The vacuum chamber is cooled to room temperature" the vacuum is released and the film is coated NESA plate removed from the chamber. X-ray diffraction does not reveal any crystallinity in the film. When examining the photoconductive spectral sensitivity, it is observed that the photoconductive edge "'is extended by about -900 Angstroms towards longer wavelengths. It is also of interest that the crystallization temperature measured by differential thermal analysis is about 20 % higher lies than that of pure selenium. '.

Example II

The according to the method of Example I with a vitreous Cadmium Selenium Coated Plate is forex- » graphically used * the plate is due to all® corona discharge

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charged to a positive potential of about 300 Y and exposed for about 2 seconds to a ^{100 watt Wolfpam “light source” at a distance of ^ O «6 1} + cm (16 in) in order to generate a latent electrostatic image on its surface. Then Tiird develops the latent image © by! On containing the image Fläch® © in electroscope's sign materials cascaded wircU The gildvt-jiyd transferred to a sheet of paper and ¥ ärmeg®sinfeei? Tg to make permanently to it. Through this process ia®vü®n copies © ines originals of good quality.

Using the method of Example I, a film is produced on a NESA substrate, which has a matrix of vitreous ICadminium and selenium in the approximate range. ¹ ^ -O % of a disP ^er> gi ^eiä ^ ^en -B infe @ 2? Ai®diar or long-range ordered crystalline phase eafeSxalten. Babei, the cadmium-containing Ti © £ gel μό heated a Temperäur of about 375 G ⁰

According to Example I, a film is applied to a NESA substrate which has a matrix of vitreous cadmium and selenium, which contains about 30 % of a dispersed, intermediate or long-range ordered crystalline phase. The substrate is heated ^{to about I 1} K) ^{0 C.}

According to Example I, a film is applied to a NESA substrate.

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brings "which has a matrix of vitreous cadmium and selenium" which is about 30 % of a .dispersed. contains intermediate or long-range crystalline phase. Thereafter, the film and the substrate for about 5 minutes is heated to a temperature of about 12O ⁰ C '.

Example VI

According to the method of Example I "- a 19 micron thick film is applied to a NESA substrate which contains about 5% lead and 95 % selenium 803 ° C. while the crucible containing the selenium is kept at a temperature of 217 ° C. The evaporation is carried out in about 2 hours. X-ray diffraction results in a glass-like structure without any apparent crystallinity. The absorption edge of this material occurs at around 1.1 microns. At around 7000 Angstroms, an increase in the phctc sensitivity is achieved »whereby at over000 / msström a third of the photosensitivity of the peak value 3s is observed. A stationary photoconductivity is observed beyond the absorption edge (approx 1 »2 H5, kron) The absorption edge and the photoconductive edge are far from the corresponding edges of either PbSe or Selenium The ability of the vitreous Biffei-Eelen-I material is between that of selenium and Pb-Se. The electronic properties of this glass material are drastically different from the properties of the

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Components or a crystalline compound of the components different.

Example VII

The plate according to Example VI is then according to the xerographic Process according to Example II charged exposed and developed, in order to produce a legible copy of an original image.

Example VIII -

According to the method of Example I a 2k micron thick film of about 8 ^r ß> zinc and 92% of selenium is produced on an aluminum substrate. During the evaporation of the components is maintained which the zinc-containing crucible at a temperature of about ⁰ C ^ Fil and the crucible containing the selenium at approximately 217 ° C. This film examined by X-ray diffraction shows no crystalline structure. Compared to vitreous selenium, the photoconductivity edge extends by about 700 angstroms towards longer wavelengths. The fundamental absorption edge of crystalline ZnSe is about V700 Angstroms, so that crystalline ZnSe cannot be used for the extended spectral sensitivity.

Example IX

The plate according to Example VIII is made according to the xerographic Method according to Example II charged, exposed and developed, to generate a readable copy of an original image.

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Example X

Following the procedure of Example I, a film having about 25% of cadmium and selenium S 75 is generated. During the evaporation step, the crucible containing the cadmium is kept at a temperature of 356 ^° C. and the crucible containing the selenium is kept at a temperature of 217 ^° C. X-ray diffraction gives a glass-like structure.

Example XI

Following the procedure of Example I, a film containing about 10% Zn and about 90 % selenium is produced. The zinc-containing crucible is maintained at a temperature of about 385 ° C and the i £ Len crucible containing · at a temperature of about 217 ⁰ C. X-ray diffraction shows no crystallinity of this film.

Example XII .

According to the method, a film having nachBeispiel I et \ m is 20% bismuth and 80% selenium prepared. Of the bismuth-containing crucible is maintained at a temperature of about 7:51 ⁰ C and the selenium-containing crucible at a temperature of about 217 ° C. The resulting glass-like film is used as a xerographic infrared photoreceiver by exposing the plate charged according to Example II and developing it. By using filters "which cut off all visible light and only transmit radiation with a wavelength greater than 8200 Angstroms", good images are produced.

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A number of other such selenium-bismuth films have been produced. Femilms are 10 to 30 µm thick and cover a composition range of up to 30 atomic bismuth. Their vitreous character has been confirmed by X-ray and electron diffraction. Most electro-optic measurements were performed on a "sandwich"layers' using gold and banners HESA Elektröden carried out for the compositions tested are the dark conductivities (300 ⁰ K) is between 10 ^"6 0hm" ¹ cm ^"1 and K 10 0hm ^-1 cm " ¹ ^ A change of only about 5 atoms in the bismuth concentration shifts the maximum spectral sensitivity from 0» 9ev to 1 «8ev. The band gaps derived from investigations of the spectral sensitivity correspond to those _s which are obtained from a resistance temperature diagram «

ft *

Additional measurements AEEA i \ x \ product and the cooldown ^ ₀ at hocheingesfcrahlten photon fluxes (no Fankgbereich) gave for ein® composition an effective mirkoskopische mobility of ₍₇ + u / U) 0-10 ^ ^"3 Cm / Volt» seconds.

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The infrared detector material yields Se-Bi D values at a peak sensitivity wavelength (−1.1 / u) of up to 7 × ¹⁰ "10 cm / watt" * seconds ¹ ' ² , which is advantageous compared to the values for PbS cells Response times in the range of 0 ₉ 1 milliseconds to 1 millisecond have been measured.

Following the procedure of Example I, a film is made with about 20 % Wlsmuth and 980 % phosphorus. The bismuth

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containing Tie £ el is maintained at a temperature of about 75l ° C and the phosphorus-containing crucible at about 187 ⁰ C This film shows in X-ray diffraction a glassy structure. .

EXAMPLE XIV

Following the procedure of Example I, a film with about. Produces 15 % zinc and 85 % boron. The crucible containing the zinc is kept at a temperature of about 385 ° ^C and the crucible containing the boron at a temperature of about 2100 ° _Λ . The boron is evaporated by electron bombardment. When examined by X-ray diffraction, no eristallium is found.

Example XV

Following the procedure of Example I, a film containing 25 % cadmium and 75 % sulfur is produced. The cadmium-containing crucible is maintained at a temperature of about 356 ⁰ C and • the sulfur-containing crucible at a temperature of about 100 °. When examined by X-ray diffraction, a glass-like structure is found.

Example Xffl

According to the method of Example I a 10 fo zinc and 9Ü $ l of sulfur is prepared containing film. The zinc-containing crucible is maintained at a temperature of about 385 ⁰ C and the crucible containing denSchwefel on a Jempcratur of about 100 ⁰ C. During an investigation

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by X-ray diffraction ", no crystallinity is found.

Instead of the components and compositions specifically specified in the examples, other suitable materials can also be used and methods as exemplified above were used with similar results. Furthermore can also have more. Materials are added which improve the properties of the panels or otherwise modify.

- patent claims -

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Claims (1)

Patent claims: 1. A method for producing a vitreous semiconductor, characterized in that a metal and a non-metal are heated at the same time to form vapors of these components that the vapors are transported to a substrate and that the vapors auf'dem substrate in the form of a vitreous Semiconductor film are deposited. 2. The method according to claim 1, characterized in that »that the vapors are deposited on a cold substrate whose Temperature is below the melting point of both components. 3. The method according to claim 1 or 2 »characterized in that that the temperature of the sub-cancer is increased, whereby a second intermediate or long-range ordered phase is formed by crystalline material which disperses in a matrix of a vitreous non-crystalline phase will. k. Method according to one of Claims 1 to 3 »characterized in that the semiconductor is reheated to a temperature above its solidification temperature for a period of time which is sufficient to obtain a second intermediate or _long- range ordered phase of crystalline material in a matrix of a vitreous non-crystalline phase. . ^l - 109820 / fSfl- bad 5 »Method according to one of claims 1 - '+, thereby characterized »that the metal concentration is increased to the formation of a second intermediate or long-range ordered Cause phase of a crystalline material in a matrix of the vitreous non-crystalline phase. 6. Semiconductor component produced by a method according to claims 1-5 * characterized by a thin Layer of a vitreous semiconductor, at least one metal and at least one non-ferrous metal that is solid at room temperature contains 7. Semiconductor element according to ^ nspruch 6, characterized s that the metal from the group cadmium, zinc, gallium, lead, thallium, indium and bismuth and that the non-metal is made of the selenium group "boron", arsenic, carbon, phosphorus and Sulfur is selected. 8. The semiconductor element according to _a nspruch 6, characterized in that the metal is selected from de group r, zinc, gallium, lead, thallium, indium and bismuth is selected cadmium and that the metal is selenium. 9 ». Ball) IeIt element according to claim 6, characterized thereby that the metal cadmium and the non-metal selenium. 2.0 * semiconductor element naoh claim 6, characterized gekenndaß the metal 2ink and daa: non-metal is selenium. 11 »Semiconductor element according to claim 6, characterized in that that the metal is bismuth and the non-metal is selenium » 12. Semiconductor element according to "nspruch 6, thereby £ ekennzelehnet, that the metal is gallium and the non-metal is selenium. 13. Semiconductor element according to "Claim 6, characterized in that d'-JS is the metal thallium and the non-metal is selenium . - ■ - ■ '■ ■ You Semiconductor element according to Claim 6, characterized in that that the metal is lead and the non-metal is selenium » 15. Semiconductor element according to Claims 6 to I ¹ +, characterized by a second intermediate or long-range ordered phase of a crystalline material in a matrix of a vitreous non-crystalline phase. 16. ' Xerographic method using a xerographic plate with a conductive substrate which is coated with a photoconductive layer of a vitreous non-crystalline material according to claim 8 »characterized in that an electrostatic charge is consumed on the photoconductive layer and that d5.e on charged Layer for the formation of a latent electrostatic image on it is exposed to ^{a haster of high-energy, activating electromagnetic radiation 1 ".} SAO ORIGINAL «■ 2k - 109820/1595 17 · - Method according to claim 16, characterized in that (\ cS das l:.; T? Ntc- electrostatic image to make it less visible; enliji disgusts we ct. BATH ORIGINAL 109820/1595