CH672778A5 - - Google Patents

Description

DESCRIPTION The invention relates to a method for producing a high-phosphorus polyphosphide coating, an apparatus for carrying out the method and various uses of the coating mentioned.

Substances and materials with chained phosphorus atoms in the sense of the present description include 5 polyphosphides with a high phosphorus content (ie phosphides which remain polymers by their nature), alkali metal polyphosphids, monoclinic phosphorus and new phosphor modifications. The phosphorus substances and polyphosphide substances are produced by vapor transport reactions in crystalline, polycrystalline and amorphous form in substance, in the form of thicker or in the form of thin layers and films. Arc vaporization processes and chemical precipitation reactions from the vapor phase are used to produce thin layers. Solid-state reactions 15 are used to produce single-crystalline and polycrystalline polyphosphides. The methods of diffusion doping can be used to increase the electrical conductivity of the materials. Rectifier transitions are made through appropriate metal contacts on the Werk-20 fabrics. Thin layers of the phosphor materials in question can serve as optical coatings and coatings. Crystal powder and amorphous modifications of the materials serve as flame retardant fillers. The crystalline forms of the materials, in particular 25 in fibrous form, can be used in plastics for reinforcement, in particular to improve tensile strength.

The use of semiconductors has become increasingly widespread and important in recent decades. 30 silicon-based semiconductors are, for example, the basis for a variety of different devices, for example for junction pn junctions with rectifier action (diodes), transistors, controllable silicon rectifiers (SCR), photoelectric cells or light-sensitive diodes. The high cost of producing the required crystalline silicon and the increasing demand for semiconductors for an ever-expanding field of application have created the need to broaden the range of useful semiconductor materials.

The technically usable semiconductors of the invention have a bandgap in the range of approximately 1 to 3 eV (more precisely 1.4 to 2.2 eV); a photoconductivity ratio greater than 5 (more specifically between 100 and 10,000); a 45 specific electrical conductivity in the range of approximately 10-5 to 10 "12 (ohm-cm) -1 (more precisely, a specific electrical conductivity in the range of 10 ~ 8 to 10 ~ 9 (ohm-cm)" 1) ; and chemical and physical resistance under operating conditions under normal environmental conditions. Even if numerous materials, which can neither be classified as pure metals nor as pure insulators, are considered semiconductors, only those semiconducting materials can also be regarded as technically usable semiconductors in the sense of the invention which meet the criteria mentioned above.

In view of the demand for the development and development of alternative energy sources that are independent of petroleum, the potential commercial importance of a semiconductor increases sharply if the semiconductor material also has usable photoelectric characteristics, i.e. is able to convert solar energy into electrical potential with reasonable efficiency at economic conditions.

From an economic point of view, amorphous semiconductors, in particular in the form of thin layers, are preferable to semiconductors in the form of single crystals because of the lower production costs for the amorphous layers. Amorphous semiconductors also have polycrystalline properties

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Semiconductors made of the same material have more favorable electrical characteristics when used in a wide variety of semiconductor components.

For the reasons mentioned, the semiconductor industry is committed to an intensive search for new semiconducting materials beyond the field of crystalline silicon.

As crystalline semiconductors containing no silicon, single crystals of GaAs and GaP and InP have been introduced as semiconducting substances in commercial practice.

Many other semiconductor materials have also been used for special applications. For example, CdS and selenium are used as photoconductors in many copiers.

In the context of the present description, the term “semiconductor element” denotes a product, including the bare semiconductor material, regardless of whether this product has or requires electrical contacts, for example is an electronic component, or can be assigned to a non-electronic area, for example an in the copying technology used photoconductor, a phosphor or a phosphor on the screen of a cathode ray tube.

Although it is known per se that some phosphor modifications are semiconducting, most phosphor substances have not found practical application as semiconductors because of their chemical instability, easy oxidizability and high reactivity. No known modification of the phosphor has so far been used successfully as a commercially suitable semiconductor.

Of the substances disclosed below

III-V semiconductors such as gallium phosphide and indium phosphide with their tetrahedral configuration can be clearly distinguished. In particular, the semiconductivity of these III-V semiconductors is not determined by phosphorus-phosphorus bonds, i.e. the electrical conduction in these materials does not take place, or at least not primarily along phosphor-phosphorus bonds.

Furthermore, hydrogenated phosphorus is known to have a structure similar to black phosphorus and to be semiconducting.

One led by H.G. von Schnering's group has done a remarkable job in the field of high phosphorus polyphosphides. The reports from this working group show that the highest link of the phosphor polymeric polyphosphides, which this working group could represent, is a crystalline MPi5, where M stands for an alkaline earth metal. These polyphosphides are made by heating the metal with phosphorus in a sealed ampoule. In Schnering's publications, the polyphosphides are to be understood as substances with atomic bonds in the classic sense due to their crystal structure. The publications state that, in other words, the substances are or should be insulators or semiconductors, but do not show metallic conductance.

The monoclinic phosphor, also known as Hittorf's phosphorus, is produced according to the state of the art from white phosphorus and lead as follows: 1 g of white phosphorus and 30 g of lead are slowly melted in a sealed tube by heating to 630 ° C and then briefly Time kept at this temperature. The solution is then cooled at a rate of 10 ° / d over 11 days to 520 ° C and then quickly quenched to room temperature. The product obtained is then electrolyzed in a solution of 2 kg of lead acetate in 8 1 6 percent acetic acid, the phosphorus being collected and collected in a watch glass which is under the anode. In this way, almost square plate-like crystals are obtained, the dimensions of which are in the range of approximately 0.2 mm × 0.2 mm × 0.05 mm.

The crystal structure of this known monoclinic phosphor modification has been determined by Thum and Krebs. The unit cell consists of two layers of pentagonal phosphor columns, all of which are aligned parallel to each other and on these two layers a second pair of layers of pentagonal phosphor columns that are parallel to each other, the columns in the second pair of layers being arranged perpendicular to the phosphor columns in the first pair of layers. The analysis of the crystal structure also determines the space group, the bond angle and the bond spacing. The summary of this prior art can be found in the "Phosphorus" section in the 1974 book "The Structure of the Elements" by Jerry Donahue.

No publications have appeared on the electrical properties of the crystals of Hittorf see phosphor. This is probably due to the fact that the crystals, which are only available in small dimensions, can hardly be measured electrically.

The production of high-purity phosphor with a grade corresponding to electronic requirements is an unusually complicated and time-consuming process according to the prior art, so that phosphor with electronic grade quality is extremely expensive.

On the other hand, the prior art also shows a need for stable phosphorus compounds which are used in particular as flame retardants and flame retardants. The crystalline forms can also be used to reinforce plastics, glasses and other materials.

The processes, apparatuses and high phosphorus-containing polyphosphide coatings according to the invention are characterized in the preceding patent claims.

In the context of the invention, a “polyphosphide” is understood to mean a material whose characteristics are determined by multiple phosphorus-phosphorus bonds. A “usable semiconductor” is understood in the sense already explained above not only as a material whose specific electrical conductivity lies in the intermediate range between an insulator and a metal, but as a material that also has a variety of other usable characteristics and properties:

- stability

- Elastic material structure

- Bandgap in the usable range (typically 1 to 2.5 eV)

- High specific electrical resistance, but can be doped

- good photoconductivity

- Luminescence with good efficiency

- Possibility to form junction junctions, especially for rectification purposes

- Can be produced at relatively low temperatures (for semiconductors) by a process that can be carried out on an enlarged scale for industrial production

- Ability to form large amorphous layers

- Possibility to form supple polymer fibers.

The polyphosphides which are the subject of this patent request are now surprisingly materials which all have the features mentioned above.

It is equally important that the usable properties of the material over a wide range of che5

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mixing composition and physical modification (crystalline and amorphous) are preserved.

As far as the applicant is aware, the polyphosphides are the only practically usable semiconductors in which the characteristic data measured in the single crystal are retained even in the amorphous state of the material. This is of the greatest technical importance because the amorphous modifications are generally more accessible. This feature is also important for applications with larger-sized devices, for example photoelectric cells, large-area display screens and electrostatic copiers.

The main problem which has hitherto opposed the extensive use of amorphous semiconductors in the prior art is that a stable single-phase material cannot be produced with the known materials, or not easily. However, even if the amorphous material can be manufactured in a single phase, such amorphous materials generally have to accept the loss of important characteristic data which show the single-crystalline phase.

The most important known semiconductor, silicon, has a crystal structure with tetrahedral coordination. Any attempt to produce amorphous silicon has so far still led to the breaking of the tetrahedron-coordinated bond structure, in the wake of which unsaturated valences occur, which decisively adversely affect the semiconductor properties of the silicon. Pure amorphous silicon is technically worthless. It is unstable and crumbly. Attempts to saturate the unsaturated valences of amorphous silicon with hydrogen or fluorine have so far been only partially successful.

It must be assumed that the preservation of the technically interesting and usable properties of the polyphosphides is due directly to the structure of these materials, which in turn is due to the very specific properties and behavior of phosphorus, in particular its ability to form polymers , which are characterized by three covalent phosphor-phosphorus bonds in the vast majority of all phosphor sites in the lattice.

In crystalline form, the MP15 polyphosphides (with M = Li, Na, K, Rb, Cs) have a structure consisting of a phosphor structure with parallel phosphor columns with a pentagonal cross section. These phosphor columns with a free inner channel are linked to one another in the manner shown in FIGS. 4, 5 and 6 via P-M-P bridges. The assembly for this atomic MP] 5 framework can be viewed as a P8 structure (composed of two rigid P4 assemblies) and an MP7 assembly (composed of a rigid MP3 assembly and a P4 assembly).

On the basis of the assemblies or clusters described above, Kosyakov (Russian Chemical Review, 48 (2), 1979) theoretically showed that the polyphosphides can be regarded as polymers in which the basic assemblies can be regarded as monomers. It should therefore be possible, at least in principle, to construct a large number of atomic structures with the same phosphorus skeleton.

During the work on the present invention, the applicant has synthesized MPi5 crystals and substances of the type (MP7) a- (P8) b synthetically using the various processes described in more detail below, the parameter b being substantially larger than the parameter a. These new substances with a high phosphorus content were originally obtained in the form of "fibers", "whiskers" or "tapes" and are referred to briefly as MPX in the context of the present description, the parameter x having a value of substantially greater than 15. These materials with a low metal concentration are produced by transport reaction via the vapor phase in the form of thick layers (greater than 10 [in polycrystalline fibers) and large spheres (with a volume greater than 1 cm3) with an amorphous character. The polycrystalline fibers show the same morphological behavior as the KP15 whiskers.

The structure of the first crystalline MPx material (x much larger than 15) that the applicant was able to produce is determined by a phosphorus framework that is similar to the phosphorus framework of the MPI5 substances.

Measurements have shown that the usable electrical and optical data of the crystalline materials MP] 5 and MPX (with x much larger than 15) are similar and comparable. The properties of these materials are therefore determined by the numerous covalent P-P bonds of the phosphorus framework, this phosphorus framework having a coordination number of slightly less than 3. Surprisingly, however, the applicant has found that the usable electrical and optical properties of these materials, namely for MPI5 and MPX (with x much larger than 15), which are present in the crystalline material, are also retained in the corresponding amorphous material.

In contrast to other previously known materials, a rigid one-dimensional structure is present in this case, which can only be described as elastic in the sense explained below. The crystal symmetry of the polyphosphides is very low (triclinic). Obviously, this slightly symmetrical material is able to adapt to the increasing structural disorder that characterizes the amorphous state in the transition from the crystalline to the amorphous structure. During this transition there is no breaking or breaking of strong tetrahedral bonds (coordination number 4) as in silicon, since the phosphorus with its significantly lower coordination number can absorb greater structural disorder than silicon without forming unsaturated valences. The polyphosphides are polymeric in nature. An amorphous polymer structure is thus obtained in the transformation, which has no detectable maxima in the X-ray diffraction spectrum. Nevertheless, the local ordering structures go further than is the case in conventional amorphous semiconductors. All observations indicate that the transition from the crystalline to the amorphous phase in the case of the polyphosphides in the structural sense results in a gradual onset of the amorphous state, this gradual onset and entry into the amorphous state being the reason for the retention of the crystalline material properties and characteristics to be observed also in the amorphous state of the polyphosphides.

The chemical composition and the structure of the family of polyphosphides clearly differentiate these substances from all previously known usable semiconductors:

Group 4a (crystalline Si, amorphous Si'.H, etc.)

3a-5a (III-V) (GaAs, GaP, InP, etc.)

2b-6a (II-VI) (CdS, CdTe, HgCdTe, etc.)

Chalcogenides (As2Se3)

lb-3a-6a (CuInSe2)

The alkali polyphosphides (MPX, M = Li, Na, K, Rb, Cs; with x = 15 and x much larger than 15) are characterized by a particularly high phosphorus content. Substances with

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especially large values for x are almost pure phosphorus. Nevertheless, due to their crystal structure (parallel pentagonal columns or tubular columns) and their properties (chemical and physical stability, band gap, specific electrical conductivity, photoconductivity), these substances are also clearly of all known phosphor modifications (black, white / yellow, red and violet / Hittorf) distinguished. The structural relationships among these various modifications are discussed in detail below.

The many allotropic forms of elementary phosphorus are evidence of the diversity and complexity of the bonding relationships and structures that phosphorus can assume or that are accessible with phosphorus. Nothing is currently known about the exact mode of action of the alkali metal in the development of the individual phosphor structures, but the data available to date indicate that the alkali metal stabilizes the phosphorus in such a way that a single specific structure from the variety of potentially possible and available structures are set and stabilized.

Without the presence of at least some alkali metal, the following undesirable phenomena are observed:

A) The phosphor is unstable (e.g. white phosphor).

B) To the extent that phosphorus can be present as a single fiber at all, it can only do so at high temperatures and with a grain size (for example violet phosphorus) limited from the range of the microcrystals, or

C) at high pressure (e.g. black phosphorus).

D) Without the presence of alkali metal in a particular batch, the MPx structure is not formed by the vapor phase transport reaction. Instead, the phosphorus is obtained in the form of the twisted fiber that was found in the course of the work on the present application. However, this crystalline phase is metastable and the structure is not particularly well developed, as shown by the X-ray diffraction spectra, the Raman spectrum and the photoluminescence data.

The presence of alkali metal during the vapor phase transport reaction promotes the formation of strictly parallel undistorted phases. Under these conditions, the formation of large monoclinic phosphor crystals at different temperatures is also favored.

The predominant role of the structure and not the composition as the decisive determinant for the properties of the substance can be seen from the fact that KPx (6x much larger than 15) has properties (band gap, photoluminescence, Raman spectra), which are essentially the data from KP15 correspond, but differ from the corresponding data of monoclinic phosphorus.

It should be emphasized that even the smallest amounts of alkali metal can be used to select the formation of stable phosphor phases. However, the question remains whether other elements that are not alkali metals can do this. Krebs reports on alkali metal-free polyphosphides with hollow column structures of the formula 2b-4a-P14 (2b = Zn, Cd, Hg and 4a = Sn, Pb). How do these structures come about?

It would be conceivable that the hollow column structure is formed with these substances because the element of the fourth main group of the periodic table of the elements is am-photer and can replace phosphorus atoms on phosphorus sites.

On the basis of the ionization energies of the alkali metals, which are all equal to or less than 5.1 eV, the apparent electron affinity in the P15 lattice, better P15 partial lattice, can be calculated. These results can then also be used to calculate the apparent ionization potentials for the other possible compositions, for example also for the 2b-4a-P14 substances. All substances in this group of materials investigated by Krebs have apparent ionization potentials of less than or at most equal to 4.8 eV.

The present development is based on the initial finding that KP13 whisker single crystals are stable semiconductors with a band gap of 1.8 eV in the red range and have both photoconductivity and photoluminescence with sufficient efficiency. This data is characteristic of semiconductors that are potentially suitable for practical use in the field of electronics and optics. The whiskers of the other MP15 substances containing alkali metal also have these characteristics (M = Li, Na, Rb, Cs).

In the following, special processes for the production of the polyphosphides with different compositions and morphological characteristics are described.

A. Condensed Phase (CP) Synthesis

This means a process in which an initial charge is first heated isothermally, then annealed at a constant temperature and then cooled again, this heat treatment being carried out in a container with the smallest possible volume. Under these conditions there is practically no vapor phase transport. This process (“CP”) is used to manufacture crystalline and polycrystalline MP15 in bulk.

B. Synthesis by vapor phase transport using a single source (1S-VT)

The starting reaction mixture is located in a zone of an evacuated tube that is heated to a temperature Tc that is greater than a temperature Td, where Td is the temperature or temperatures of one or more other zones of the evacuated tube where the target product is from the vapor phase precipitates. This process can be used to produce: Crystalline MP] 5; crystalline, polycrystalline (in substance and in the form of thin layers) and in substance amorphous MPX with large values for x; monoclinic phosphor; star-shaped fiber material; and twisted phosphor fibers.

C. Synthesis by vapor phase transport using two different sources (2S-VTJ

The starting substances with which an evacuated reaction chamber is charged are physically separated from one another, the precipitation zone for the product being arranged between the two source zones. The two sources are heated to temperatures which are higher than the temperatures of the precipitation zone in order to obtain at least amorphous material; (see below). The precipitation zone need not be the coldest zone in the system, but the coldest zone in the reactor should only be able to condense a single component of the vapor phase. 2S-VT was the first process to produce thin amorphous layers of KP15. Polycrystalline and amorphous thin layers of MP] 5 and thin polycrystalline layers and amorphous substance of MPX with high x values can be produced in this way.

D. Quenching from the melt

An exit feed is sealed in a

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and the evacuated tube is heated (if possible isothermally) to a temperature which is greater than the melting point determined by the differential thermal analysis. The feed is kept at this temperature for some time. The tube is then removed from the oven and quickly cooled. In this way, a CsP7 glass was made.

E. Rapid evaporation

The powdery feed material is placed under slowly flowing argon in a receptacle that is heated at high frequency in the range of the radio frequencies. The temperature of the collecting vessel is kept at temperatures higher than approximately 800 ° C. Inside the vessel, the material is passed through a labyrinth in which it at least theoretically comes into contact with the hot surfaces. The feed should be evaporated quickly and completely in such a way that the resulting steam flow has the same composition as the powder applied. The vapor stream is then directed into an evacuated chamber where it encounters colder surfaces where the product condenses. In this way, amorphous layers can be obtained.

F. Chemical vapor phase precipitation reaction (CVD)

This term is generally used for a process for the production of materials, in which at least two starting components are mixed in the vaporous state in which they are to react chemically with one another to form the target products. For example, Applicants K and P4 independently and dosed into furnaces where they evaporated rapidly and were carried away to cooler zones of the reactor by a stream of argon. There the substance of the intermixed steam flows was reflected as a chemical reaction product and target product in the condensed phase.

The importance of deposition from the vapor phase after chemical reaction in the vapor phase (CVD) is that this method is ideally suited for the technical scale and for doping in situ, i.e. for doping the target product simultaneously with its manufacture. This process was used to produce thin KP15 layers in the course of the tests carried out here.

G. Precipitation from a Molecular Stream (M FD)

This vapor phase transport process is a process in which the starting substance is evaporated from several sources and essentially corresponds to a combination of the 2S-VT process type and epitaxial growth from a molecular beam («MBE»). Independently heated evaporation sources are used to evaporate the starting substance, the flow of the evaporated molecular particles or fragments being controlled in a manner not achievable in the 2S-VT method in such a way that the molecular flow reaches the likewise independently heated substrate at exactly predetermined rates. The precipitation takes place in an evacuated chamber, the progress of the current condensation from the vapor phase being monitored in a manner which is also not achieved in the 2S-VT method. The reaction chamber can either be hermetically sealed or continuously evacuated to monitor the vapor pressure.

A large variety of polyphosphides of various physical forms and chemical compositions were produced at the beginning of the applicant's investigations.

In the course of the work, interest shifted from single crystal growth to the production of amorphous materials, both in substance and in the form of large thin layers, for reasons of practical application.

Among all MP] 5 materials, KP15 is a crystalline material with a high phosphorus content, which in the K-P system 10 of the MPx systems with x values equal to or greater than 7 is unusual due to its characteristics. (In contrast, the other alkali metals with phosphorus only form substances in which x has the value 7 or 11, for example CsP7, NaP7, RbPn, etc.). KP ,, and KP7 cannot be isolated as 15 substances of solid chiometry. For this reason, the K-P system can be monitored and controlled more easily than other alkali metal-phosphorus systems, in which several different, stychometrically composed substances can form.

20 Furthermore, the experimental work of the applicant shows that in all cases in which potassium and phosphorus are evaporated, regardless of the means or method by which this evaporation is carried out, and in a corresponding 25 atomic evaporation ratio ([P] / [K] equal to or greater than 15) are transported into a zone whose temperature is in the correct and usable temperature window, amorphous KP15 is formed. The “temperature window” is a temperature that is low enough to prevent crystallization of KP15 and at the same time large enough to prevent KPX from precipitating with x much larger than 15.

Based on these findings and this teaching, it can be seen that all different synthetic processes in the case of the production of KP] 5 can be operated according to the same basic principle. Each of these methods uses only different means for regulating and controlling the evaporation source and regulating or controlling the precipitation of the target product. The evaporation processes, which work with two sources (2S-VT, CVD and MFD) are particularly economical to use, since the decisive process parameters can be controlled and regulated independently of one another.

45 On the basis of the considerations given above, amorphous KP15 in the form of thin layers has been selected by the applicant as a model substance for the development of new usable semiconductor materials in the field of polyphosphides.

50 Potassium polyphosphide whiskers approximately 1 cm in length were made by evaporation using a single evaporation source to further investigate the properties of the polyphosphides. X-ray diffraction studies ensure that the single crystals obtained and measured are actually KP15 crystals. The semiconducting behavior of these whiskers is also checked. When the whiskers thus produced are exposed to an argon laser at 4 K, a photoluminescence occurs which corresponds to a energy emitted of 1.8 eV when measured. This value indicates that a band gap in the same energy range can be expected for the investigated material.

To measure the specific electrical conductivity of these whiskers, electrical connection wires are attached with Sil-65 ber contact pastes. The safe contact from the supply lines via the silver paste to the crystal is monitored microscopically during the conductivity measurement. It is surprisingly shown that

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slide the monitored crystals in the microscope and thus different electrical conductivities are measured when the exposure of the crystals changes. Accurate measurements have shown a photoconductivity ratio of 100, while the specific electrical conductivity of the unlit whiskers is approximately 10 ~ 8 (ohm-cm) "'. The specific electrical photoconductivity as a function of the wavelength, the optical absorption, was then used to determine the bandgap of the whisker material measured as a function of the wavelength and the temperature dependence of the specific electrical conductivity of the whiskers. All these measurements confirmed the photoluminescence measurements at 4 K in that the whisker material has a bandgap of approximately 1.8 eV. In this way it could be ensured that the KPl5- Whisker crystals were to be classified in the circle of potentially usable semiconductor materials. An amorphous coating is formed on the inner wall of a quartz tube during the production of the KP15 whiskers by vapor phase transport. A band gap of the order of magnitude is also formed for this amorphous layer ng of 1.8 eV and a photoconductivity ratio of the order of magnitude of approximately 100 was measured. Like the crystalline whiskers, the amorphous layer has a specific electrical conductivity of approximately 10-8 (ohm-cm) -1. In this way, it was experimentally ensured that the amorphous material is at least a potentially exploitable semiconductor material.

The applicant then faced the question of whether KP] 5 could also be grown in the form of larger single crystals, such as silicon, and would be accessible in this form for the production of semiconductor material. It was also examined whether polycrystalline or amorphous layers of KPI5 could be produced reproducibly and were suitable and usable for the production of semiconductors. Then the material produced during the vapor phase transport tests had to be precisely analyzed and identified and the question had to be clarified whether analog materials would also have the same practically usable characteristics.

After numerous vapor phase transport experiments, the applicant was then astonished to find that the substances obtained using only one single vapor and potassium mixture containing phosphorus mixed with one another resulted from heating the source and condensing the vapor phase reaction product at the other end of a closed reaction tube were obtained did not correspond to the composition KP15, but corresponded to the composition KPX on the basis of the chemical wet analysis carried out, where x was in the range from approximately 200 to approximately 10,000 according to the wet analytical results.

The subsequent intensive systematic investigations by the applicant have led to the surprising result that the affinity of the phosphorus for potassium or any other alkali metal in vapor phase transport reactions using a single evaporation source leads to the initial deposition of MP1S as the most stable polyphosphide. In the presence of excess phosphorus, however, a new form of phosphorus then forms as condensate, which corresponds to the chemical composition MPX with x values of much greater than 15. These new forms of phosphor surprisingly have the same electronic characteristics and qualities as KP] 5 and can be classified as valuable semiconductor materials.

The intensive tests carried out for the production of thin layers of polycrystalline and amorphous KP] 5 and the analogous substances with other alkali metals have shown that such layers do not form if the starting substances are mixed with one another for carrying out the vapor phase transport reaction from a single evaporation source were evaporated. For this reason, the applicant has developed a process for the synthesis of the substances by vapor phase transport reaction, in which the starting substances are evaporated from two separate evaporation sources. According to these processes, the alkali metal and the phosphorus are thus heated separately and independently of one another and evaporated from sources arranged independently of one another. With simultaneous control and regulation of the temperature of a thermally separated intermediate precipitation zone, thin MP15 layers can be obtained in polycrystalline and amorphous form, wherein in the above formula M can be any alkali metal. This two-source process also made it possible to produce thin layers of polycrystalline and thick layers of amorphous phosphor material of the new form, as well as other obviously polymeric materials of the formula MPX, in which M is an alkali metal and x has a value that is much larger than 15.

The processes of extremely rapid evaporation, precipitation after chemical reaction from the vapor phase and precipitation using a molecular stream were also used to produce the materials.

The uniform general chemical formula MPX is used to label all polyphosphides produced by the process according to the invention. Practically usable semiconductors are obtained for values of the parameter x in the range from 7 to infinity. The alkali metal polyphosphides to which the chemical formulas MP7, MPn and MP15 correspond are known. Substances of the general chemical formula MPX in which the parameter x has values of much greater than 15 are described and new for the first time in the context of the present invention.

Vapor phase transport reactions are also used to produce these substances, in which a single evaporation source is used to evaporate the starting substances. By regulating the precipitation temperature and in particular by keeping the precipitation temperature constant over larger precipitation areas, these processes, which are known in principle, are decisively improved. This also enables large-area thick layers and spherical substances in polycrystalline and amorphous form with the chemical composition MPX to be obtained, in which x has values of much greater than 15.

Large quantities of crystalline and polycrystalline material with the chemical composition MP] 5, where M is an alkali metal, have been prepared in such a way

that stoichiometric proportions of alkali metal and phosphorus were mixed together and heated isothermally. This process for producing condensed phases leads to excellent material of the composition MPX with values of the parameter x in the range from 7 to 15. This process can be carried out well in vapor phase transport reactors with an evaporation source. This process can be made more effective by homogeneously mixing and grinding the alkali metal and the phosphorus in a ball mill before charging the evaporation source. The ball mill is preferably heated to a temperature in the range around 100 ° C. for mixing. Surprisingly, relatively stable powder mixtures are obtained.

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The product studies have shown that all polyphosphides with structures that are characterized by parallel hollow columns, bandgaps in the range of 1.8 eV, photoconductivity ratios of much larger than 5 with measured ratios in the range of 100 to 10,000 and a low conductivity in the range from 10 ~ 8 to 10-9 (ohm-cm) -1.

This shows that the amorphous forms of all these materials, i.e. the alkali metal phosphide MPX with x values greater than 6, which are formed in the presence of an alkali metal, have at least essentially the same semiconductor properties, so that it is obvious that the short-range order of the amorphous materials is similar to the short-range order of the crystalline materials and overall parallel pentagonal tubular columns are marked over essentially the entire area of the amorphous phase.

In all polyphosphides, the three covalent homoatomic phosphorus-phosphorus bonds dominate and determine the electrical conduction paths through the structure on the vast majority of all phosphorus sites and are much more important than all other bonds, with the phosphorus-phosphorus bonds overall establishing semiconductor properties.

All of the material's phosphorus atoms, which are cross-linked and interconnected by covalent bonds, together form the predominant electrical conduction path through the material, whereby the crystalline short-range regions characterized by the parallelism of the alignment give rise to the good semiconductor properties. The phosphorus atoms are trivalent in these structures, the chaining of the atoms leading to the formation of spirals or columns with an internal hollow channel. The alkali metal atoms, if present in the structure, connect the individual chain sections of the structure to one another. Atoms other than phosphorus, especially if they are trivalent and are capable of forming three covalent homoatomic compounds, should also be able to form semiconductors of this type.

So described are new forms of phosphorus and processes for their preparation, solid layers of amorphous or polycrystalline MPX and process and a device for their production, process and device for the production of metal phosphides by vapor phase transport processes with multiple controlled temperatures using a single evaporation source, process and Device for the production of polyphosphides with a high phosphorus content by vapor phase transport processes using several separate evaporation sources, process and device for the production of MP15 in polycrystalline form by solid-state reactions, semiconductor components which contain polyphosphide groups with at least seven phosphorus atoms covalently interconnected and arranged in pentagonal hollow columns and a band gap of greater than 1 eV and having a photoconductivity ratio in the range of 100 to 10,000, semiconductor devices, d ie contain a substance of the composition MPX, in which M is an alkali metal and x is greater than 6, and materials with bandgaps of greater than 1 eV and photoconductivity ratios of 100 to 10,000, semiconductor components, made from a material that contains very large proportions of one consists of chain-linked, covalently bonded trivalent atoms, preferably phosphorus-containing material, in which the chain-connected atoms are linked to one another by several covalent bonds and have short-range order, which contains layers of linked atoms which are arranged parallel to one another in each of the layers, and wherein the Layers are also arranged parallel to one another, and the linkages preferably form pentagonal hollow columns, semiconductor components which contain an alkali metal and the above-mentioned linked structures, in which the number of successive covalent linked bonds is sufficient nd greater than the number of bonds that are not in the chain, that the material is semiconducting, semiconductor components made from compounds which contain at least two linked assemblies, each of which has a framework of at least 7 atoms covalently linked to one another, preferably phosphorus atoms, and There are alkali metal atoms which conductively connect the framework of one unit to the framework of another unit, junction components, methods for producing such semiconductor components, methods for doping such semiconductor components, methods for conducting an electrical current and finally methods for generating electrical potential differences using such devices.

The main idea is therefore to create or make available a new class of substances of valuable semiconductor materials, within which a part of the individual compounds is new and is described here for the first time, while another part of the substances included in the class itself is known, but has not been recognized as a substance equipped with technically applicable and utilizable semiconductor properties.

All of these materials have a band gap in the range of 1 to 3 eV, preferably in particular in the range of 1.4 to 2.2 eV, particularly preferably around 1.8 eV. The photoconductivity ratios are at values greater than 5, in fact in the range between 100 and 10,000. The specific electrical conductivity of these materials is in the range from approximately 10 "5 to 10 ~ 12 (ohm-cm) ~ ', so it has one Magnitude in the range of 10 ~ 8 (ohm-cm) -1.

On the basis of the present description, the person skilled in the art will readily recognize that the alkali metal component M of the polyphosphides or other corresponding trivalent “ide”, which are capable of forming homoatomic covalent bonds and correspond to the general chemical formula MY, can also contain a number of akali metals Combinations of these metals can contain, which can «simulate» a binding behavior corresponding to the binding behavior of the alkali metals, and which contain these metals in arbitrary proportions, without changing the basic pentagonal hollow column structure and without thereby significantly influencing the electronic semiconductor characteristics of the material.

Also described is a method for doping the materials according to the invention with iron, chromium and nickel to improve the specific electrical conductivity of the substances. Contact barrier layers were produced and measured using Al, Au, Cu, Mg, Ni, Ag and Ti using silver contact paste and point probes.

The incorporation of arsenic into the polyphosphides with parallel hollow columns also leads to an increase in the specific electrical conductivity.

The semiconductor materials and the devices and components of the invention can be used in a variety of ways. The following may be mentioned in areas of application for the materials of the invention: photoconductors, in particular in photocopiers; Light emitting diodes; Transistors, diodes and integrated circuits; Photoelectric application5

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areas; Metal oxide semiconductor devices; optical sensors and scanners; Phosphors for excitation by photons or electrons as well as numerous other semiconductor applications.

In the context of the present invention, the applicant has for the first time also produced large monoclinic phosphor single crystals. These crystals are obtained using the vapor phase transport technology, starting with MPi5 feeds or feeds in the form of mixtures of M and P with various variations in the concentration ratio (M-P). Surprisingly, these large monoclinic single crystals of phosphorus contain considerable amounts of alkali metals (500 to 2000 ppm were observed). These crystals cannot be grown under the same conditions if there is no alkali metal in the feed.

Two different crystal habit are observed for these large phosphor crystals.

The crystals of one habit have a truncated pyramidal crystal shape. These crystals are particularly difficult to split. The other habit corresponds to the platelet-shaped crystal formation, which is easily split.

The largest crystals had dimensions of the order of 4 mm • 3 mm • 2 mm (height). The largest crystals that could be obtained in the habit shown in Fig. 40 are approximately square, have an edge length of approximately 4 mm and a thickness of 2 mm.

The crystals have a metallic appearance in the reflection and are dark red in transmission. Chemical analysis shows that the crystals contain in the range of 500 to 2000 ppm alkali metal. The X-ray diffraction diagrams obtained from polycrystalline powder samples, the Raman spectra and the differential thermal analysis all have at least essentially identical structures and data such as the known Hittorf see phosphorus.

The photoluminescence spectrum of the crystals grown in the presence of cesium and of the crystals grown in the presence of rubidium show luminescence maxima at 4019 cm-1 and 3981 cm-1, respectively. This results in a band gap of approx. 2.1 eV at room temperature for this monoclinic form of the phosphor.

The invention is explained in more detail below on the basis of exemplary embodiments in conjunction with the drawings. Show it:

1 shows a schematic representation and partly in section of a device for carrying out the vapor phase transport reaction with a single evaporation source;

FIG. 2 shows a schematic illustration of part of the vapor phase transport reactor according to FIG. 1;

3 shows a schematic representation of a further simple device for carrying out the vapor phase transport reaction;

4 shows a schematic illustration of an experimental reactor tube for the vapor phase transport reaction with two evaporation sources;

5 shows the temperature profile in the reactor according to FIG. 4;

6 shows the course of the concentration ratio of phosphorus to potassium in the experimental reactor shown in FIG. 4;

7 shows a schematic representation of a device for carrying out the vapor phase transport reaction using two evaporation sources;

FIG. 8 shows a schematic representation of one of the elements of the device shown in FIG. 7;

9 shows a schematic illustration of a further reaction tube for carrying out the vapor phase transport reaction using two evaporation sources;

10 shows a schematic illustration of a ball mill, as can advantageously be used 5 to implement the invention;

11 shows a schematic illustration of a closable ampoule for producing monoclinic phosphorus;

12 is a side view and a schematic representation of a device for immediate substance evaporation; FIG. 13 shows a section according to 48-48 in FIG. 12;

FIG. 14 shows a cross section according to 49-49 in FIG. 13; and

15 shows a schematic representation of a device for carrying out syntheses by precipitating the product after a chemical reaction from the vapor phase. 15 Wherever possible, the same reference numbers are used for the same parts in the figures.

In the manner shown in FIG. 1, an oven 10 which can be operated with two temperature zones is used, the outer iron jacket 12 of which is wrapped with thermal insulation 14, for example 20 asbestos.

A mixture of phosphorus and potassium in a molar ratio of 12 to 1 is used as the starting substance 36. For example, 5.5 g of red phosphorus and 0.6 g of potassium are introduced into a glass tube 32 under nitrogen. Before that, the phosphorus is repeatedly washed with acetone and then air-dried. However, the washing process is not mandatory, but can be carried out optionally, if necessary also with another solvent.

30 After the starting mixture 36 has been charged, the reactor tube 32 is evacuated, in this case to 10-4 mbar, melted and then introduced into the furnace 10. In this case, the tube 32 is arranged in the furnace at a slight incline in such a way that the feed with the starting substances 36 to be evaporated are lower than the tube head shown on the left in FIG. 1. The zones of the furnace are supplied with electrical energy via supply lines 24 and 26 in such a way that the temperature gradient from the heating zone 28 to the heating zone 40 30 drops from, for example, 650 ° C. to 300 ° C. The part of the reactor tube is in the region of the higher temperature zone 28, in which the starting substances 36 are arranged.

If the furnace 10 has been operated under the conditions mentioned for a sufficiently long time, for example approximately 42 hours, the supply of electrical energy via the leads 24 and 26 is stopped and the pipe 32 gradually cools down. After reaching the ambient temperature, the tube 32 is opened under a nitrogenate atmosphere and the contents of the reactor tube 32 are removed. The reaction product is washed with CS2 to extract pyrophoric fractions. This leaves approximately 2.0 g of stable end product. This corresponds to a yield of approximately 33%.

55 When using this type of synthesis, different product phases are formed, which occur at precisely defined locations within the reaction tube 32 (FIG. 2). A dark gray-black precipitate 40 in connection with a yellow-brown film 42 typically occurs at the extreme 60th end of the hot zone 28, where the starting mixture 36 is initially arranged. When advancing in the direction of lower temperatures within the tube 32, a black to purple thin precipitate 42, which is 65 as a polycrystalline material, is then observed at these areas 40 and 42. Following this precipitation layer 42, a sharply delimited dark ring of massaged crystallites 44 occurs. Immediately adjacent to crystallites 44 is a bright zone, in which whiskers 46

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have grown. This is followed by a highly reflective precipitation layer 48, which is formed on the lower part of the reaction tube 32 at the beginning of the colder zone 30. A deep red precipitate 50 occasionally appears over the rainfall layer 48, the occurrence of this fog depending on the temperature maintained in the cooler zone. The precipitates 48 and 50 can be polycrystalline, amorphous or mixed polycrystalline and amorphous, depending on the type of substances used and the temperatures set in the individual case. At the outer end of the cooler temperature zone 30, a purely amorphous material 42 is deposited as substance or fitting.

Since a continuous temperature gradient occurs in the arrangement shown in FIGS. 1 and 2 from the hot to the cold zone in the reaction tube, the type of material deposited is also subject to a continuous change from high-quality single-crystal whiskers to polycrystalline and amorphous materials. For better control of the reaction and for the specific creation of certain precipitation areas with larger and uniform areas, a three-zone oven of the type shown in FIG. 3 is preferably used instead of the two-zone oven. This three-zone furnace 54 is essentially the same as the furnace 10 shown in FIG. 1 and consists of an outer iron jacket 56, a refractory inner tube 60 and the reaction tube or ampoule 58. For better clarity, the asbestos insulation of the Outer jacket 56 and the insulation of the tube 58 not shown in FIG. 3. The furnace 54 differs from the furnace 10 in that the tube 58 is significantly longer than the reaction tube 32, in this case 48 cm long. In addition, the furnace 54 has three separate heating zones 62, 64 and 66, which can be controlled individually, so that a better-defined temperature gradient can be set over the length of the furnace inner tube 60. The inner tube 60 of the furnace can be mounted on asbestos blocks 68 and 70 in such a way that the inner tube 60 and the reaction tube 58 located in it are given an incline which drops towards the hot zone 62 in order to ensure that the feed 36 is adequately stored.

Method 1 (see FIG. 3)

The 50 cm long reactor tube, which contains the reactants, is stored within a second quartz tube in the 61 cm long heating chamber of the furnace. By setting the control points of the three heating zones of the furnace accordingly, an at least substantially linearly falling temperature gradient can be generated. A temperature gradient AT / d can thus be generated, where T is the temperature and d is the respective axial distance in the furnace, is at least approximately constant between the centers of the two outer heating elements. This linear temperature gradient, which is applied over the longer dimension of the reaction tube, serves the purpose of separating the various product materials formed during the reaction. The products appear in a very specific pattern and in a very specific sequence with decreasing deposition temperature: first dark purple to black polycrystalline films, then a ring of massaged crystallites; Single crystals or whiskers, red layers with small grain size and polycrystalline morphology; and, in the coldest temperature range of the reactor tube, a dark gray amorphous material.

A series of experiments has shown that this amorphous material does not form in the sealed reaction tubes if the coldest temperature of the tube is greater than approx.

Is 375 ° C. Similarly, the occurrence of the red polycrystalline material can be significantly suppressed by maintaining the lowest temperature on the reactor tube at or above 450 ° C. Furthermore, the applicant has determined that polycrystalline MP15 cannot be manufactured in devices that operate with a single evaporation source. The polycrystalline and amorphous substances formed here are substances with high values of x, in which x is much larger than 15.

Procedure 2

The brackets wound from the woven tape not only serve to align the reaction tube, but also as effective barriers against the heat transfer between the three heating zones. These barriers cause a steeper temperature drop between the zones, but at the same time a flatter gradient within the central zone. As a result, a stepped temperature profile is obtained which can be set and manipulated in such a way that specific target products can be obtained selectively by setting the corresponding precipitation temperatures.

A) In von Schnering's announcement of the production of single crystals (whiskers) by KPI5, he described the production from the elements in that the heating of the elements, namely potassium and red phosphorus, in a «temperature gradient» of «600/200 C» in one about 20 cm long quartz tube. He further states that the crystals formed in the temperature range from “300 to 320 ° C”. The furnaces used were obviously single-heater furnaces where the temperature gradient is caused by the heat loss that occurs at one end of the tube that protrudes from the furnace.

As a first step in improving this method, a three-zone furnace of the type shown in FIG. 3 is used to carry out the method according to the invention, in which the heating of the output elements can be monitored and controlled independently of one another. In addition, the heating chamber of the three-zone oven used (Lindberg model 54 357) has a length of 61 cm, making the temperature gradient applied easier to monitor and regulate. By storing the reaction tube, which now had a length of approximately 52 cm, in a second quartz tube open on both sides, which is supported on asbestos blocks. In this device, a generally linear profile of the temperature gradient AT / d is set, which is at least approximately constant between the two centers of the two outer sides of the heating elements of the furnace. The electrical power input to the furnace is monitored using a Lindberg controller (model 59 744 / A). This device uses three independent controllable controllers, which contain independent controllable silicon rectifiers and band controllers, which control the oven temperature according to the manual preselection.

The linearly falling gradient, which is maintained and imprinted over the long dimensions of the reaction tube, serves to cleanly separate the various products that are formed in the course of the reaction. These products occur in a characteristic sequence of precipitation with decreasing temperature: dark purple to black polycrystalline films, a ring of massaged crystallites, single crystals or «whiskers»; fine-grained red films with polycrystalline morphology and, in the coldest area of the reaction tube, dark gray amorphous substance.

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Example I

A three zone oven (Lindberg, Model 54 357) as shown in Fig. 3 with heating elements buried in a refractory material, in separate cylindrical sections 15.3 cm, 30.6 cm and again in lengths 15.3 cm (corresponding to 61 cm in total) is used to carry out this example. The diameter of the heating chamber is 8 cm. The temperature is taken from thermocouples, not shown in the figure, which are arranged, measured over the length of 61 cm of the inner stovepipe.

The sides of the heating chamber are clogged with glass wool to minimize heat loss from the stove. A quartz tube with a length of 60 cm and a diameter of 4.5 cm is inclined at a slight angle and placed on asbestos blocks in the heating chamber.

The quartz reaction tube has a round base in axial section, is 49 cm long and has a diameter of 2.5 cm. The reaction tube then has a section with a narrow cross section, which is 10 cm long and has a diameter of 1.0 cm. 6.51 g of red phosphorus and 0.62 g of potassium are introduced into the tube under a dry nitrogen atmosphere. The atomic ratio of phosphorus to metal is 13.3 to 1. The phosphorus has analytical purity. The tube is evacuated to a pressure of 10 ~ 4 mbar and tightly closed by melting the extension tube. A few centimeters of the extension pipe remain. The total length of the pipe including the neck is 51.5 cm after melting. The reaction tube thus sealed is placed in the three-zone furnace described above. The temperature in the three heating zones is set to 650 ° C, 450 ° C and 300 ° C. This temperature distribution is used for heating for 5 hours. The temperature is then held for a further 164 hours. Then the power supply is switched off so that the furnace can cool down to room temperature. This takes place at the cooling rate inherent in the arrangement. The reactor tube is then cut open in a glove box under a dry nitrogen atmosphere. Condensed phases with crystalline, polycrystalline and amorphous morphology are obtained as products.

Polyphosphides have been produced in two fundamentally different types of plants, both of which are referred to in this description as "two-source plants" with reference to the production process with two independent sources, because in both plant types the metal and the phosphorus are heated separately and independently from each other on both sides of the precipitation zone. All tests described here were carried out in the K-P system.

According to the first method, which is shown schematically in FIG. 4, the phosphorus batch and the potassium batch are arranged at the two opposite ends of a fused glass tube 100. The tube is exposed to a temperature profile of the type shown in FIG. 5, this temperature profile being generated in a three-zone furnace. The profile brings the independent and separately arranged feeds to an increased temperature, namely increased relative to the central zone, which is arranged between the two zones which contain the starting components. In this central zone, the components of the starting products are combined to form the product precipitate KP15, in the form of coatings on the walls of the reactor tube.

The second type of system is shown schematically in FIG. 7. An essential part 102 of the reactor tube 134 protrudes from the three-zone furnace 104 and is at ambient temperature. This section contains a control valve 106 and a spherical ground joint 108 for leak adjustment of certain negative pressures at which the reaction is to be carried out. With this alternative technique of closing the reactor tube, this closing section does not need to be exposed to the same high temperatures as during melting. The wide access opening to the tube also allows the introduction of glass boats that contain the phosphorus or the metal, which is not possible due to the tapered neck of the melted reaction tubes. The boat 112 (FIG. 8) is also constructed in such a way that metals deposited on a glass substrate 114 (FIG. 7) can be brought into the condensation zone, on which the product layers can and should be deposited. These film / substrate configurations serve as the starting point for the construction of components, as will be explained in more detail below.

The section of the reactor tube outside the furnace serves as a cold trap for the vapor particles. In particular, the phosphorus located in the zone of the reactor tube closest to the outlet side is deposited in large quantities in this outer section, generally in the highly pyrophoric form of the white phosphorus. Due to the presence of this cold trap, the vapor pressure conditions in the system of FIG. 7 are significantly different than in the closed-heated system described above. From this it is readily understandable that the temperature conditions selected for the manufacture of the products in the system described above can in no way be successfully transferred to the system described here. The reaction parameters, in particular temperature parameters, suitable for the two-source method described here had to be determined again.

Example V

A 54 cm long and 2.5 cm diameter quartz tube 100 with a 10 cm long and 1.0 cm diameter side nozzle 116 (FIG. 4) is charged with phosphorus and potassium under dry nitrogen, the substances lying opposite each other Ends of the tube are filled. The molar atomic ratio of the phosphorus to potassium feed is 15 to 1. The potassium (99.95% pure) is initially charged in such a way that a small piece of potassium, which weighs 0.28 g, is introduced into a collecting beaker 118, the longitudinal axis of which is directed coaxially to the longitudinal axis of the reactor tube. The potassium pieces filled into the cup are then melted and solidified again in the cup. The phosphorus (degree of purity 99.9999%) is then introduced in pieces in an amount of 3.33 g into the reactor tube and without difficulty around the cup 118. The reactor tube is then melted under reduced pressure on neck 116. The pressure during melting is 7 • 10 ~ 5mbar.

The reactor tube, which has been charged and melted, is then placed in a three-zone furnace of the Lindberg Model 54 357-S type in such a way that the three temperature zones are centrally symmetrical to the furnace tube. In contrast to the oven model No. 54 357 used in the previous experiments, the zone lengths of 15.2, 30.5 and

15.2 cm, the zone lengths in the S model used for this experiment are 20.3, 20.3 and

20.3 cm. Two asbestos fabric tapes spirally wound on the reactor tube support the reactor tube in the transition areas between heating zones 1 and 2 or 2 and

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3. These asbestos tapes not only carry the reactor tube, but they also isolate the central area from the higher temperatures of the adjacent outer zones. The temperature profile obtained and set in this way is shown schematically in FIG. 5. The three heating zones are operated under the guidance of a computer (Honeywell model DCP-7700) in such a way that they generate temperatures of 450, 300 and 450 ° C in the three zones after heating, these gradient temperatures being maintained for 72 hours. Following this dwell time, the system is systematically controlled and regulated to room temperature over the course of 15 h.

The product substances obtained in the reactor tube are analyzed. For this purpose, the reactor tube is first cut into 7 sections of equal length in a dry nitrogen atmosphere, using a silicon carbide cutting disc. The coatings found in the sections on the pipe walls are removed and individually examined by X-ray. The rest of the product yield in each area is subjected to wet chemical analysis.

The P / K ratios of the precipitates which were determined in the individual sections of the reactor tube identified in FIG. 6 are also shown in FIG. 6. For the medium range, in which the temperature T is approximately 300 ° C., the substance compositions have a ratio of approximately 14 to 1. Within the accuracy of the methods used for the analysis, this analytical value falls within a range that can be expected for the substance KP15. The X-ray diffraction diagrams recorded on powder samples were more unambiguous for the substances, for which a ratio P to K of approximately 14 was determined by wet chemistry, the X-ray recordings unquestionably matching the spectra of KPi5, both in the form of the single-crystal whiskers and for the polycrystalline material. Furthermore, the X-ray diffraction patterns clearly detect the presence of both crystalline and amorphous material, in a ratio of approximately 1 to 1. This estimate is based on the observed broadening of the diffraction reflections.

example VI

The system also used in example V is used. The quartz tube 119 is provided with additional “nozzles” 120 and 122, which separate the two side chambers from the middle chamber (FIG. 16). Under dry nitrogen, 0.47 g of molten potassium with a purity of 99.95% is added to the outer chamber of the reactor tube shown on the right in FIG. 9 and marked with “K”, the melted KaHum then being solidified there. The feed pipe 124 is then sealed by fusing. Subsequently, on the other side of the chamber, identified by “P” in FIG. 9, phosphorus in a quantity of 5.58 g with a purity of 99.9999% is added. Then the entire reactor tube is evacuated to 10 -5 mbar and sealed by melting. After the individual nozzle 126 has melted, the reactor tube contains phosphorus and KaHum in a molar atomic ratio of 15 to 1.

The sealed reactor tube 119 is a total of 41 cm long and is arranged centrally in the three successive 20.3 cm long heating zones of the three-zone furnace (Lindberg, model 54 357-S). Two heat barriers (TB) made of woven asbestos tape, which is wound around the pipe in increasing spirals, hold the pipe at the transitions from Zone 1 to Zone 2 and from Zone 2 to Zone 3. In addition, the middle zone is separated from the two outer ones Zones thermally insulated by the asbestos holders. A computer is used to control the three time zones of the furnace (Honeywell, model DCP 770). The three zones of the furnace are heated to 500, 355 and 700 ° C under computer control. The phosphor is heated to 500 ° C, the KaHum to 700 "C. The middle zone is heated up to only 300 C by the temperature preselection, but due to the incomplete insulation by the fabric band, heat transfer from the side hot zones occurs the inner colder zone so that the actual temperature in this central precipitation zone is 355 ° C. This temperature profile is maintained for 80 h and then the furnace is cooled in the course of 24 h.

The reactor tube 119 is then sawn open under dry nitrogen, using a silicon carbide cutting disc. This shows that the nozzle 122 between the potassium zone and the central zone was blocked with a substance which, according to optical assessment, resembled a multi-fiber KPI5. Thin red fittings, thicker dark red fittings and a number of relatively large pieces of monolithic substance were found in the central zone. The two largest pieces each had a length of around 4 cm, a width of 1 cm and a maximum thickness of about 4 mm. One side of each of these pieces was relatively flat, while the opposite side was convex, since this side grew on the round walls of the reaction tube.

Wet analysis of this material showed that the substance has an extremely low potassium content, after analysis of the substance less than 60 ppm. Electron spectroscopic examination and analysis (ESCA) shows that the potassium content of this substance increases with distance from the reactor tube walls on which the precipitate initially began to form

decreases rapidly. At a distance of 10 nm, the P / K ratio is already approximately 50. The ESCA measurements of the P-K ratio on the final surface of the deposited material show a value of the order of 1000. The X-ray studies show that the substance is amorphous.

Example VII

Under dry nitrogen, 0.19 g of potassium melt (99.95% pure) are placed in one of the outer sections 128 (5 cm long) of a Pyrex boat 112 (FIG. 15). The metal is solidified there. Two flat glass substrates 114 (see FIG. 7), each about 7.5 cm long and 1 cm wide, are placed side by side in the boat so that they fill the 15.3 cm long central section 130. Then 1.36 g of phorphor (99.9999% pure; obtained from Johnson Matthey) are introduced on the opposite side 132 of the boat. The phosphorus is granular, with a mixed grain size. The granular phosphorus is flowable and easily fills the bottom of section 132 of the boat. The cross dividers 113, which are also made of Pyrex glass, prevent the phosphorus and the potassium as well as the substrates in the boat 112 from slipping into one another. The boat 112, which is a total of 35 cm long, is then carefully pushed into a Pyrex tube which serves as the reactor chamber 134 and is 60 cm long and 2.5 cm in diameter (FIG. 7). The boat is pushed into the reactor tube until the section 128 of the boat, which is filled with the KaHum, abuts the round bottom 136 of the Pyrex tube 134, which is closed on one side. An size 124 O-ring made from butadiene nitrile rubber is then inserted into the O-ring coupling 102. The Teflon control valve 106 (ChemVac, Ine) is then

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tightly closed. After connecting to a vacuum line, the control valve 106 is then opened again and the chamber is pumped down to a pressure of 10-3 mbar. After reaching this pressure, the valve is closed again and the reactor chamber is hermetically sealed.

The reactor chamber is arranged in a three-zone furnace (Lindberg, model 54357-S). In the manner shown in FIG. 7, two ribbons 137 and 139 made of glass fiber fabric are spirally wound around the tube and carry the reactor tube at the transitions from zone 1 to zone 2 and from zone 2 to zone 3. These ribbon windings form thermal barriers (TB ) and are arranged so that they are completely within the central zone of the furnace. A third spirally wound tape roll 138 serves as a support and thermal insulation at the point where the reactor tube exits the furnace heating chamber. A cylindrical plug 140 made of a ceramic-like material serves to reduce heat losses from the opposite furnace opening.

The arrangement is dimensioned such that section 128 of boat 112, which contains the potassium, lies in the region of the third furnace zone, while section 130, which contains the substrates, lies in the central region, i.e. lies in the second heating zone of the furnace, and the section 132 of the boat containing the phosphorus lies in the first heating zone of the furnace. In addition, a relatively large section of the reactor plant protrudes from the furnace and is at room temperature.

The three heating zones of the oven are computer controlled (Honeywell, model DCT 7700). During a warm-up period, the temperature in the three heating zones is brought to 100, 150 and 100 ° C. in the phosphor zone, the substrate zone and the potassium zone. The mixture is then heated to the target temperature profile of 500, 300, 400 ° C as quickly as possible, approximately in 18 minutes. The set temperature profile is maintained for approximately 8 hours. The furnace then cools down with its own characteristics until the temperature profile 100, 100, 100 ° C is reached after about 10 hours. The oven is then allowed to cool further to room temperature.

After reaching room temperature, the reactor tube 134 is removed from the furnace. The pipe section outside the furnace contains deposits of white, yellow and yellow-red substances, which are most likely phosphorus in various degrees of polymerization. The heating zone, which originally contained the phosphorus, was free of substance at this point. In contrast, the potassium zone contained a wide variety of substances, the colors of which varied from dark brown to yellow to orange.

The substances in the potassium zone also extended slightly into the area of the central zone, which was otherwise covered over its half length, adjacent to the potassium zone, with a dark coating which is transparent to red light when a corresponding light source was viewed in a transparent manner. The rest of the center of the boat was substance-free. The reactor tube is opened under dry nitrogen, the boat 112 is pulled out and the substrates covered with the red coating are removed from the boat and placed in a tightly closed vessel for later analysis. When the material remaining in the reactor tube is exposed to the ambient air, the phosphor deposits in the released areas of the tube burn relatively violently, even if those areas closest to the phosphorus source did not show as much reactivity. The substances remaining in the potassium zone or in the area of the potassium source reacted violently if they did so

Exposure to moisture. Most of them burned down violently, which is obviously due to the formation of hydrogen through water reduction.

Boundary conditions are set for the production of the dark, red-translucent layers. If the temperatures in the two source zones are slightly reduced, for example in Experiment No. 49 in Table XII, the amount of product material formed decreases drastically, which is reflected in a reduction in the length of the deposit or the precipitation in the central zone. In the same way, the subtle differences in the performance characteristics of the two otherwise identical models of the three-zone furnaces used for these tests must be taken into account. For example, the temperature of the phosphorus source had to be kept higher in the second oven (B) (cf. Experiments No. 50, 51 and 52). Increasing the temperature of the phosphorus source to 550 ° C leads to good results, while increasing to only 225 ° C leads to much better results.

The analysis of the substances obtained in experiments No. 46, 47 and 48 is carried out with a scanning electron microscope using the electron diffraction analysis (SEM-EDAX). The analysis showed that the layers are KP15 layers with a thickness of the order of 6 to 7 ^ m. The layers are amorphous without any structural elements being recognizable in the scanning electronic micrographs.

(3) The use of thermal barriers to improve temperature gradient design;

(4) using heat plugs on the face of the stovepipe; and

(5) Use of tube extension sections with a narrower cross section for the production of cylindrical substance pieces.

The following process parameters must be observed for the single-source vapor phase transport process:

(1) reaction zone temperatures in the range of 650 to 550 ° C; the cold precipitation zone should have temperatures in the range of 450 to 300 ° C;

(2) The precipitation temperature for KP15 single crystals is in a range of ± 25 ° C around a central value of 465 to 475 ° C.

(3) The precipitation temperature for polycrystalline layers is in the range from 455 ° C down to 375 ° C;

(5) The precipitation temperature for the amorphous forms of the new phosphor forms are in the range from approximately 375 ° C down to at least 300 ° C (the applicant has not yet tested any lower temperatures).

The framework for the process parameters for the two-source vapor phase transport process for the production of solid KP, 5-substance pieces in a device according to FIG. 4 can be specified as follows: phosphorus source temperature at 450 ° C., potassium source temperature at 450 ° C and precipitation zone at 300 ° C. The precipitates are relatively thick layers of mixtures of polycrystalline and amorphous KPI5. For the production of lumpy amorphous KPX (x much larger than 15; a new form of phosphor; device according to FIG. 9) phosphor at 500 ° C, potassium at 700 ° C and precipitation zone at 355 ° C. The potassium source tends to clog, the precipitate is massive amorphous KPX. For thin amorphous KP15 layers (device according to FIG. 7): phosphorus at 500 ° C, potassium at 400 ° C and substrate at 300 ° C.

For thin layers of KP15, the temperature of the phosphorus source can be raised up to 525 ° C, whereby amorphous KP15 is still formed. If the temperature of the phosphorus source drops below 475 ° C, in the

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System no KP] 5 received. If the temperature of the potassium source drops below 375 ° C, the KP15 will also no longer be retained in the system. The substrate temperature can be raised to 315 ° C, with good yields of KP15 being obtained even at this temperature. KP15 will no longer be obtained if the substrate temperature is raised above 325 ° C.

Production of polycrystalline metal phosphides in large quantities by the solid-state reaction process

Even if the alkali metal polyphosphides of the types MP15, MP7 and MPn cannot be produced in a physical state that enables direct exploitation of the semiconductor properties, which are in a favorable range, these substances can, however, in gram quantities and larger quantities by the process known as the solid-state reaction getting produced. Before the process is carried out, the reaction components are mixed well with one another in a ball mill. Amounts of the order of 10 and more grams of the elements are placed in a ball mill under nitrogen in the required molar atomic ratio of phosphorus to metal, for example P / M 15 to 1 for MP15. After the ball mill has been firmly closed, milling is carried out for at least 14 hours in order to comminute, homogenize and convert the starting elements into a free-flowing powder. The ball mills are preferably heated to approximately 100 ° C. for approximately 20 hours during milling. This measure can improve the flowability of the metal component during milling.

A portion of the milled mixture, generally at least 10 g, is transferred to a quartz vial and sealed under dry nitrogen. The quartz ampoule usually has a diameter of approximately 2.5 cm and a length in the range from 6.5 to 25 cm, depending on the size of the feed to be processed. The ampoule is closed under reduced pressure, generally at pressures of less than 10 -4 mbar.

The reaction is carried out in such a way that the sealed ampoule is heated under isothermal conditions until a temperature in the range from 500 to 525 ° C. is reached. In the context of the description, “isothermal conditions” means that the entire mass of the material, as far as this is possible and feasible, is always at the same temperature in order to suppress the transport of steam from hot to cold areas in the feed, which is the reason for this Formation of non-homogeneous reaction products would give. The highest temperature at which the feed is annealed is maintained for a long time, during which time the powdery polycrystalline or the coarse crystalline product forms at the annealing temperature. The dwell time for annealing is usually 72 hours. The longer the reaction is carried out at the annealing temperature, the more crystalline the product becomes, which results in an increase in the grain size, a sharpening of the X-ray diffraction reflections and other corresponding characteristic data. The cooling of the hot reaction tube or the ampoule to room temperature usually takes place over a longer cooling period, which is preferably in the range of greater than 10 h. The slow cooling is not important for the reaction, but prevents cracking of the quartz ampoule due to different coefficients of thermal expansion of the product formed and the material of the ampoule, namely the quartz.

Both the heating period and the cooling period should, if possible, be designed to be relatively long, preferably at least 10 hours, with a tempering phase at intermediate temperatures of, for example, 200, 300, 400, 450 ° C. for 4 to 6 hours. If these rules are not followed, the sealed ampoules tend to explode. However, the products of the solid state reactions are the same as 5 for slow cooling, with the exception that the small amounts of residual phosphorus are white instead of red.

Example VIII

19.5 g of a mixture 10 of analytically pure phosphorus and potassium ground in a ball mill in a molar atomic ratio of 15 to 1 are placed in a quartz ampoule with a length of 6.5 cm and a diameter of 2.5 cm. The ampoule ends in an 8 cm long neck, which has a diameter of 1.0 cm. The feed is carried out in a dry nitrogen atmosphere. The ampoule is then melted under reduced pressure (10-4 mbar), leaving about 1 cm of the narrowed area.

The sealed tubular ampoule is held in the middle zone of a three-zone oven (Lindberg, model 54357) in a second quartz tube or lining, which in turn is mounted on asbestos blocks on the central axis of the oven tube. The heating elements of the three-zone oven are controlled by a computer (Honeywell, model 25 DCP 7700), which can be used to reproducibly control a pre-programmed heating program. The reaction tube or the ampoule are reproducibly subjected to the following temperature profile: 100 DC, 1h; 450 ° C, 6h; 500 ° C, 18h; 525 ° C, 72h; 300 ° C, 2h and 200 ° C, 30 4h. If all three zones of the furnace are set to the same temperature, the central zone of the furnace is extremely isothermal, with a temperature variance of less than 1 ° C over the entire zone.

After the furnace has cooled down again to ambient temperature 35 with its own characteristics, the ampoule is removed from the furnace and opened under dry nitrogen with a silicon carbide saw. A dark purple polycrystalline mass is removed from the ampoule. The wet analysis of the product shows a P / K ratio of around 40.2 to 14.2 to 1, this value corresponding to the theoretical value of 15 to 1 within an accuracy of approximately 6%.

While the type of alkali metal used does not appear to be particularly critical for this crystal growth 45, the temperature at which the feed is kept is obviously of greater importance for crystal growth. In the case of the Cs / Pu feed, where the feed was previously ball milled and mixed, large single crystals are obtained when the feed is kept at a temperature in the range of 555 ° C to 554 ° C. However, if the feed is kept at temperatures around 565 ° C or around 554 ° C, large monoclinic phosphor single crystals can no longer be produced.

55 FIG. 11 shows the preferably used apparatus with which the tests are carried out.

RbPi5 produced by solid-state reaction in an amount of 0.6 g is melted in a vacuum into a glass tube 270 which has an outer diameter of 12 mm, a 60 inner diameter of 6 mm and a length of 8 cm. The top of the glass ampoule is melted in such a way that a flat glass surface 272 measuring 16 mm in diameter is obtained. A single nozzle 274 is provided with a constriction 276, on which the ampoule 65 is melted off after loading.

The ampoule filled and melted in this way is exposed to a temperature gradient in such a way that the flat surface 272 at the upper section of the ampoule or

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of the reactor tube is kept at a temperature of 462 ° C, while the feed at the bottom of the tube is kept at a temperature of 550 ° C. After a dwell time of 140 hours at this temperature, approximately half of the feed originally abandoned has been transported from the floor to the flat upper surface.

A button-like piece of substance is obtained as the product, which is split and tested. This piece of substance consists practically exclusively of homogeneous light red fibers and not the large monoclinic phosphor single crystals actually expected.

The differential thermoanalytical data are similar to the data obtained for polycrystalline material with high x values in the MPX system. The DTA examinations showed a first heat plateau in the form of a single endothermic level at 622 ° C (on average). A second heat plateau consists of a single endothermic level in both cases at 599 ° C. The DTA data previously recorded on polycrystalline material with large X values secured for this material a first, non-split endothermic plateau at 614 ° C and a second, also non-split endothermic heat plateau at 590 ° C. In other words, the DTA studies on the twisted fibers showed essentially the same results as those obtained for fibrous phosphorus obtained from 99.9999% pure red phosphorus and polycrystalline phosphorus-rich material of the MPX system. Stable thin layers in the form of amorphous coatings on glass and nickel-coated glass as substrate material can be produced using the rapid evaporation method («flash evaporation»). A device with which such rapid evaporation can be carried out is shown in FIG. 12. The evaporation device 302 essentially consists of a glass cylinder 304 which can be connected via a line 306 to a vacuum system, not shown in the figure. The inlet connection 308 is supplied with argon via a feed line 310. A reservoir 312 is charged with powdery KP15, which has previously been produced by a solid-state reaction. The feed is moved with a vibrator 314. The shaken feed is then carried along by the argon stream through the venturi 316. The entrained feed substance then enters reactor 304 via the feed line

317 in a steel vessel 318. The steel receptacle

318 is heated to a temperature of at least 900 ° C. by a high-frequency coil 319, the KP1S carried in the argon stream evaporating immediately. At the end of the line 317, nozzles 320 with a plurality of small openings 321 are arranged by inserting a plurality of narrow-sized tubes. The line 317 and the tubes 320 are made of aluminum oxide, the tubes 320 being anchored in the tube 317 with magnesium oxide cement 322.

The KPI5 dissociates into its components during evaporation. The vapor thus formed is discharged from the argon through the nozzle-like openings 321. The product layer is then deposited on a cooler substrate 324 arranged in front of the nozzles. The substrate can be heated with the aid of heating wires 326, which are fed via electrical connecting wires 328. The alumina tube 317 has an outer diameter of approximately 0.64 cm and an inner diameter of approximately 0.32 cm. The tubes 320 each have an outer diameter of approximately 0.16 cm and are approximately 0.64 cm long. They have small through holes.

The system is operated in a vacuum at pressures from 0.1 to 0.9 mbar. Amorphous layers of thickness up to 1 | jm can be obtained when the system is operated for up to 15 minutes. At the end of each run, the substrate 324 reaches a temperature of 200 to 300 ° C, depending on what temperature the substrate is at the beginning of the precipitation, at room temperature, or whether it is preheated to 200 ° C.

Thin KP 15 layers are also produced by chemical reaction in the vapor phase with subsequent precipitation of the product (CVD).

A typical CVD reactor is shown in FIG. 15. The reactor is made of Pyrex glass. The reactor chamber 401 has an outer diameter of 26 mm and is 27.0 cm long. A long tube is arranged inside the reactor, on the central axis of the reactor, which has an inner diameter of 6.0 mm and is 30.0 cm long. This long tube 402 serves both as a heat source and as a substrate holder. The heat source is held in place by an adjustable O-ring collar 403. A vent pipe 404 allows an exhaust gas to be continuously withdrawn. It is connected to a cold trap, not shown in the figure, in which the unreacted phosphorus is precipitated before the extracted gas stream is supplied to the surrounding atmosphere. The vent pipe 404 and the O-ring collar 403 are connected to the reactor chamber 401 via a flange connection 405 with an interposed O-ring and an inner diameter of 2.0 cm. The reactor chamber 401 is placed in an electrical resistance heating furnace 406.

Molten phosphorus is measured into the evaporation chamber 408 by means of a piston pump, not shown in the figures, via a capillary 407, which has an inner diameter of 1.0 mm. The molten phosphorus is evaporated in the evaporation chamber 408 by a jet of argon which is blasted in via an inlet connector 409 with an inner diameter of 6.0 mm. The gaseous phosphorus / argon stream enters the reactor chamber through a nozzle 410. The nozzle 410 has an opening of 4.0 mm. The evaporation chamber 408 is housed in a resistance heating furnace 411.

A gaseous mixture of potassium and argon is metered into the reactor chamber 401 via a feed nozzle 412 with an inner diameter of 6.0 mm. Pure argon, which serves as the carrier gas for the potassium / argon flow, enters the system via the nozzle 413, which has an inner diameter of 6.0 mm. Both the potassium / argon flow and the pure argon flow enter the reactor chamber 401 at the inlet port 414. The potassium / argon line 412 and the line 413 carrying pure argon are accommodated in an electrical resistance furnace 415.

The substrate 416 is held on the thermal source 402. The temperature of the substrate 416 is measured with the aid of a thermocouple 417, which is arranged directly below the substrate 416 on the thermal source 402.

During operation, the furnaces 406, 411 and 415 are regulated separately to the corresponding temperatures. The gaseous reactant streams arrive at the inlet ports 410 and 414 in the reactor chamber. The exhaust gas mixture leaves the reactor chamber via the vent pipe 404. The product layers that are produced in the reactor are deposited on the substrate 416.

The substrates are kept at a temperature in the range of 310 to 350 ° C. This temperature is maintained with an accuracy in the range of ± 2 ° C.

For a typical run, 1.24 g of white phosphorus and 0.13 g of potassium are added to the reactor over 2 hours. The total argon flow is adjusted to a volume flow of 250 ml / min.

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A number of experiments are carried out in which phosphorus / argon and potassium / argon are added to the reactor simultaneously. The phosphor / argon flow is maintained at a temperature of approximately 290 ° C while the potassium / argon flow is set at approximately 410 ° C. The calculated molar atomic ratio of the reactants in the reactor is adjusted so that P / K is approximately equal to 15. The reactor is kept at a temperature of 300 to 310 ° C in total. In a typical course of the experiment, the liquid phosphorus is added at a rate of 0.34 mg / h.

KP15 amorphous layers are produced using nickel-coated glass substrates. The KP] 5 layers obtained under these conditions are approximately 0.3 mm thick.

With a test run lasting 1 h, a thin layer is obtained, for which the nominal composition KPI5 is confirmed. The thickness of the layer depends on the arrangement and position of the substrate in the reactor. The scanning electron microscopic examination shows that the layers are extremely well homogeneous.

Cleaning the phosphor:

50 g of "99.95% pure" phosphorus is exposed to a temperature profile in the range of 450-300 ° C for 75 days. After this relatively long residence time, 21% of the material left behind remains in the feed and 60% of the feed is obtained as massive amorphous precipitates.

Analyzes carried out on the input material showed that the phosphorus is not even 99.90% pure, but much closer to a purity of 99.80%, this phosphorus with aluminum, calcium, iron, magnesium, sodium and silicon as main impurities which were all present in an amount of greater than 0.01% by weight, some even in concentrations of greater than 0.05% by weight. This material has a purchase price of approximately $ 220 per kg. In comparison, a phosphor sold only with the "99%" purity level has a purchase price of only US $ 37.5 per kg.

The use of the phosphorus substances as flame retardants is known. Due to the high stability of the phosphorus-rich substances containing Al-10 potassium metals, which are described in the present description, the substances described here are recommended for this purpose. Form of adherent thin films can be deposited. These films are ductile, non-porous, polymeric and 15 non-brittle.

The materials disclosed in the above description are therefore ideally suited to be used in the form of coatings and thin films. 20 The description therefore discloses a completely new class of semiconductor materials with a high phosphorus content. These semiconductor materials contain covalently bonded atoms in chains, these covalent bonds forming chains forming the primary electrical conduction path 25 in the material. The atoms linked into chains form parallel columns as the predominant near-order feature. The atoms in these chains are preferably trivalent with bond angles that enable the formation of tubular spiral or hollow channel-like columns 30. The columns can be joined together by atoms of one or more different elements in pairs or in large numbers to form linked chains.

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3 sheets of drawings

Claims (17)

672778 1. Process for producing a high phosphorus-containing polyphosphide coating by means of flash evaporation, characterized by the following process steps: Passing material through a heated vessel to evaporate the material, said flowing material comprising phosphorus and an alkali metal. 2. The method according to claim 1, wherein the flow through the material is carried out by transporting powdered material in a gas stream. 2nd PATENT CLAIMS 3. Apparatus for performing the method according to claim 1, comprising a heatable vessel and devices for allowing material to flow through the vessel, said devices for flowing material comprising means for introducing powdered material into said gas stream, - An electric winding heater around the said vessel to heat it by induction, and - A line through said vessel, which line ends in a multiple nozzle. 4. Highly phosphorus-containing polyphosphide coatings, produced by means of the method according to claim 1. 5. A method of vapor deposition of high phosphorus polyphosphides comprising driving separate streams of vaporized phosphorus and alkali metal over a condensation substrate. 6. Apparatus for carrying out the chemical vapor deposition according to claim 5, comprising: A. a heated chamber, B. a substrate in said chamber, C. Means for the gas exit from said chamber, a gas stream of a first steam component entering the chamber being surrounded by a stream of gas and a second gas stream of a second steam component also entering said chamber. 7. Coating, produced by means of the vapor deposition method according to claim 5. 8. Coating according to claim 7, characterized in that it is a protective coating. 9. Coating according to claim 7, characterized in that it is an optical coating. 10. Coating according to claim 7, characterized in that it is an anti-reflective coating. 11. Coating according to one of claims 8 to 10, applied to a glass or on a metal substrate. 12. Coating according to one of claims 8 to 10, wherein said coating is amorphous. 13. Flame retardant material obtained by the process according to claim 5. 14. filler obtained by the process according to claim 5. 15. Semiconductor material obtained by the method according to claim 5. 16. Crystalline polyphosphide in the form of rods arranged in a star shape, obtained by the process according to claim 5. 17. Use of single-crystalline polyphosphide according to claim 16 for embedding in a glass or in a plastic matrix.