DE1621328B2 - Process for the production of a semiconducting layer - Google Patents

Description

The invention relates to a method for producing a semiconducting layer, in which a binary Semiconductor is evaporated onto a substrate.

Such a method is already known from US Pat. No. 2936252. With this well-known Process which is intended for the production of layers from electroluminescent materials, In a first process step, electroluminescent monocrystals are made from the sulfides or oxides of cadmium or zinc, these monocrystals being formed by evaporation of the basic components generated in an atmosphere containing hydrogen sulfide or oxygen. These fumes are deposited on a substrate under conditions conducive to the formation of monocrystals allow. In the second process stage of this known process, the previously formed Monocrystals evaporated in a high vacuum and deposited on a translucent substrate, this substrate being heated sufficiently to allow the recrystallization of the vapor-deposited materials to ensure monocrystals.

This known method is disadvantageous in that it requires considerable technical effort and is specially designed for the production of electroluminescent layers, so that with Products manufactured with the help of the known method are not easily used for rectifiers, detectors, Photocells, transistors, etc. are suitable.

Semiconductors preferred in technology consist either of pure elements such as silicon, Germanium and selenium or from chemical compounds such as copper (I) oxide, Lead sulfide, silicon carbide, lead telluride, etc.

In semiconductor materials such as silicon and germanium, the smallest trace amounts of selected Impurities and / or crystal vacancies play a significant role in the semiconductor properties to influence or change the material.

The impurities lead to the creation of relatively freely movable electrons, which are located below Move cargo transport. On the other hand, the impurities can also get electrons out of their normally remove occupied lattice space, whereby a flaw is formed in the lattice, which is filled by a neighboring electron, whereby a new lattice defect is formed, which is then replenished in turn. The resulting flaw migration comes one electrical line in one sense of the direction, the opposite of that sense of direction that occurs during the migration of electrons.

As already mentioned, the known method for producing semiconducting layers requires a considerable technical effort, which in terms of costs is reflected in the relatively high prices of the known Expresses semiconductor layers produced in a manner.

The invention is therefore based on the object of creating a method of the type mentioned at the outset, which in a technically simple and inexpensive way enables the production of semiconductor materials or semiconducting layers permitted.

This object is inventively achieved in that a semiconductor-forming metal and a semiconductor forming solid under normal conditions nonmetal simultaneously vaporized and the vapors on a substrate, of the held anticipated semiconductor to a temperature below the melting point, deposited who ^the ·

According to one embodiment of the invention, as

Metal cadmium, zinc, gallium, lead, thallium, indium or bismuth and as a non-metal boron, arsenic, Carbon, phosphorus, sulfur or preferably selenium is used.

It has been found to be particularly advantageous that after receiving the semiconducting layer Vapor deposition at a temperature of the support which is above the melting point of the expected Semiconductor is, is continued until a crystalline layer is obtained on the amorphous semiconducting layer will.

According to a further embodiment of the invention, after receiving the semiconducting Layer to be heated above the melting point of the semiconductor until one amorphous and one crystalline semiconducting layer can be obtained on the support.

It turned out that particularly favorable

permanent process results can be achieved that more metal than the stoichiometric Amount corresponds to the layer substrate is deposited.

The semiconducting layers produced with the aid of the method according to the invention contain one thin layer of a vitreous semiconductor that we-. at least one metal and at least one at room temperature contains solid non-metal. When the evaporated components are deposited on the substrate the various atoms are randomly connected to one another, forming a continuous one and homogeneous non-crystalline film mixed on the support. These films can be used with any Thickness can be generated. Film thicknesses in the range from about 1000 Angstroms up to 200 μm and thicker are the cheapest for semiconductor purposes, but leave it alone such films can also be produced which are only a few 100 angstroms thick.

The semiconducting layers produced according to the invention can best be used as glass-like semiconductors or semi-isolators. These process products possess electrical properties that differ from those of the pure components or differ from stoichiometric compounds of these components. Obtained from these substances X-ray diffraction grids are found to be of the vitreous or non-crystalline type. This glassy Semiconductors can be described as thermodynamically metastable, although they have a high Have a degree of phenomenological stability and maintain their structure at relatively high temperatures. In some cases, the crystallization temperature of these glassy semiconductors is higher than that of the respective individual components.

The semiconducting layers produced in the manner according to the invention contain at least one solid layer or liquid metal and at least one solid non-metal. The metals cadmium, zinc, Gallium, neodymium, mercury, copper, silver, manganese, aluminum and bismuth can be considered. As according to the invention non-metals to be used are selenium, boron, arsenic, carbon, phosphorus and sulfur suitable.

The invention is explained in more detail below with reference to the drawing.

This shows an apparatus for carrying out the method according to the invention.

As can be seen from the drawing, a bell 10 rests on a base plate 11, which has vacuum lines 12 and control valves 13 encloses. For heating evaporation crucibles 16 and 17, which are to be evaporated Containing materials 18 and 19, resistance heating circuits 14 and 15 are provided. At a a bracket containing a water-cooled base 21

A water cooling device 22 is provided. A substrate 23 to be vaporized is of the water-cooled base 21 held. One at the base

21 hinged aluminum mask 24 is used to rest on the layer support 23 around the same cover until the materials to be evaporated 18 and 19 have been heated to a suitable temperature are.

The metal and the non-metal are each in a separate inert crucible, for example from Introduced quartz or hard glass. When evaporating the components, it is advantageous to adjust the temperature to keep the components mentioned between their melting point and their boiling point. Intended to For example, an amorphous cadmium-selenium layer is produced with about 20% cadmium and about 80% selenium so has a temperature of about 217 ° C for the selenium and of about 322 ° C for the Cadmium was found to be sufficient. If the amount of selenium in the film-like layer is to be increased, see above the temperature of the selenium container is increased and /

5 or the temperature of the cadmium container is lowered. However, if the amount of cadmium in the Layer are increased, the aforementioned temperature changes are carried out in the opposite sense. If a very slow evaporation rate is to be achieved, the evaporation temperature becomes one or both components are kept at a temperature below their melting points.

The vacuum chamber is maintained at a vacuum of about 2 X 10 ^-5 to 2 X 10 ~ ⁸ Torr, although a vacuum may also be used satisfactorily above or below this range. With the above conditions, a layer thickness of about 5 to 30 μm is obtained if

ao the evaporation is carried out for a time of about 1 to 3 hours, at.einem vacuum of about 2XlO " ⁵ Torr. Obviously, the amount of a certain component in the vitreous film depends primarily on the amount of the evaporated metal or non-metal, which in a It should be noted that a vitreous layer can also be formed by vapor transport or sputtering without the use of a vacuum.

The semiconducting layers can be on any conductive or insulating suitable Layer support are vapor-deposited. Brass, aluminum, and rust-free materials are used as conductive layers Steel, conductive coated glass or plastic etc. are possible. Quartz, hard glass, Mica, polyethylene etc. are suitable. In some cases it can be advantageous to use the support to be eliminated completely.

Semiconductors are usually composed of a metal and a non-metal. When laying down the boundary between metals and non-metals is a diagonal boundary known as the Zintl boundary line drawn through the periodic system to separate the metals from the non-metals. According to According to the invention, at least one element is chosen from each side of this line, which evaporates Materials are characterized by the fact that they are non-stoichiometric. Although semiconductors are made of crystalline Compounds that can exhibit slight deviations from the stoichiometry are those according to the invention Manufactured semiconductors are formed without taking into account the stoichiometry, so that considerable deviations of the stoichiometric composition of corresponding crystalline compounds general rule and a stoichiometric composition are only an exception.

The structure of semiconductors made according to the invention is more glassy than crystalline. The structure is characterized by the absence of an intermediate or long-range ordering phase, and the X-ray diffraction grids are of the so-called vitreous or non-crystalline type. These Connections cannot normally be made like glasses; H. cooled from the melt and it is not known that vitreous materials or glasses are ever made from these systems have been manufactured. However, there have been reports of unsuccessful attempts to produce them

Materials before. In particular, from "The Structure of Glass", Vol. 2, page 410, by Kolomietes et al, Consultant's Bureau, New York (1960) shows that glasses cannot be obtained when copper, Silver, gold, zinc, cadmium, mercury, gallium, indium, thallium, germanium, tin or lead together heated to 900 ° C with selenium, sulfur or arsenic and then precipitated.

With regard to their electrical properties, the materials produced according to the invention can be used as Semiconductors or semi-isolators describe what means that they have a valence and conduction band, which is separated by a forbidden energy range is. Their electronic properties are of those of the pure components and of those a stoichiometric crystalline compound of these components different. Though they are considered thermodynamic can be called metastable, they have a high degree of phenomenological Stability and retain their structure even at temperatures above room temperature lie. In some cases, their crystallization temperature is higher than the crystallization temperature of the individual components.

These vitreous materials cannot be melted by any melting technique, but only by Precipitation can be obtained from the vapor phase. In fact, many of these materials are in liquid form State immiscible well above the boiling point of one of the components. They even became glassy Systems with a metal content of up to 30 atomic percent are obtained without the support was cooled below room temperature.

According to a typical embodiment of the invention, the non-metal is selenium and one is die Elements cadmium, zinc, gallium, lead, thallium, indium and bismuth comprehensive group of metals obtained a group of vitreous semiconductors, which are especially useful in electrophotography are. These compounds show a photoconductive spectral behavior in the wavelength range of visible light up to and including infrared light. The above metals form in combination with Selenium vitreous semiconductors that can absorb an electrostatic charge and generate an electrostatic latent image when exposed to light. This image can be developed in a known electrophotographic manner, as described, for example, in U.S. Patent No. 2297691.

The material obtained by simultaneous evaporation of bismuth and selenium is for infrared radiation sensitive and can therefore be used in an electrophotographic system which uses Radiation outside the visible spectrum works. In addition, the combination of bismuth / Selenium can also be used in non-electrophotographic systems; acts in such systems these are infrared photodetectors, vidicons, light intensifying panels, electroluminescent and others electro-optical devices.

When used in electrophotography, the above materials are added to an appropriate one conductive support such as brass, aluminum, stainless steel, conductive coated Vaporized glass or plastic etc. On the electrophotographic plate thus produced a uniform electrostatic charge through a Corona discharge generated to sensitize its entire surface. The plate then comes with a Image of activating electromagnetic radiation, for example light, which exposes the charge selectively equalizes in the exposed areas of the photoconductor - while in the unexposed A latent electrostatic image remains in areas. The image can be developed or on some other material be transferred, with the development through

ίο Application of finely divided electrostatic particles on the surface of the photoconductive material takes place in order to make the so-called latent image visible do. It should be noted that any suitable method can be used to obtain an electrostatic image. Typical possible techniques exist in the use of a pen matrix in the form of a pen head, pen tubes, etc.

The inventive method allows an adjustment of the degree of order achieved, because under

ao certain conditions can have a second phase with their crystalline, intermediate or nature Long-range order can be obtained, which second phase disperses in the vitreous non-crystalline matrix is. This can firstly be achieved through suitable

»5 position the relative quantities of the two to be evaporated Components, secondly by adjusting the temperature of the substrate or thirdly by a subsequent heat treatment can be achieved. Such two-phase dispersions are considered to be uniform if they have been mixed in the vapor state in the atomic range. Secluded second phases in oxide glasses are known; these are, for example, photochromic Glasses. However, these are ordinary oxide glasses which can be produced from the melt.

In the context of the method according to the invention, the second intermediate or long-range order phase can be carried out can thereby be obtained dispersed in the vitreous non-crystalline matrix that, as mentioned above, the temperature of one of the components to be evaporated higher than the temperature the other component is increased. For example, if a cadmium-selenium layer is produced, so the selenium is kept at an evaporation temperature of 217 ° C and the evaporation temperature of the cadmium to about 375 ° C compared to a normal evaporation temperature of about 322 ° C elevated. This increase in the evaporation temperature leads to the formation of about 30% of an intermediate crystalline phase with long-range order, which is in a vitreous matrix of cadmium and Selenium is dispersed.

Such vitreous semiconductors have the same variety of possible uses as before

used semiconductors and semi-isolators. They are used as photoconductors, luminescent materials, electroluminescent

; nescent materials, circuit elements, superconductors

: ter, thermoelectric materials, ferroelectric materials, magnetic materials, in electropho-

tographic receivers etc. usable. The following Examples serve to further illustrate the process according to the invention and leave their use of the semiconductor produced according to the invention

recognize layers. The parts and percentages are.

Unless otherwise specified, parts and percentages by weight. The following examples illustrate various preferred embodiments of the invention.

example 1 Example 5

In this example, a 7 μm thick semiconducting layer with about 20% cadmium and 80% selenium is to be formed on a layer support. This layer support is a Nesa glass plate. 10 g each of cadmium and selenium were placed in separate quartz crucibles in the form of pellets. The quartz crucible was placed in a vacuum chamber in which a vacuum has been produced of about 2 X 10 ^-5 Torr. The support was applied to a water-cooled base which is positioned approximately 30.48 cm above the quartz crucible and is kept at a temperature of approximately 54 ° C. The substrate was covered with a thin aluminum mask, which was then removed when the cadmium and selenium crucibles reached their vaporization temperature. The cadmium and selenium were then evaporated onto the substrate, the temperature of the cadmium crucible being kept at about 322 ° C. and that of the selenium crucible at about 217 ° C. by means of resistance heating elements. The evaporation process ended after about _{2/2 hours.} The vacuum chamber was then cooled to room temperature and the vacuum was released, and the coated support was removed from the chamber. When examined by X-rays, the layer produced was found to be non-crystalline. When the photoconductivity properties were checked, an extension of the sensitivity range by 900 Angstroms towards longer wavelengths was found. Furthermore, with the help of the thermal analysis it was found that the crystallization temperature is around 20 ° C. higher than that of pure selenium.

Example 2

The product obtained according to Example 1 was corona discharge to a positive potential of about 300 V and for about 2 seconds a 100-watt power supply that is 16 inches away Tungsten light source exposed to a latent electrostatic on the surface of the semiconducting layer Generate image. The latent image is then developed, including on the surface containing the image an electroscopic drawing material is cascaded. The image is transferred to a sheet of paper and fixed by the action of heat. The copies of an original thus produced were of good quality.

Example 3

In the manner explained in Example 1, a semiconducting layer was deposited on the substrate, which layer has a matrix of vitreous cadmium and selenium, in which about 40% of a dispersed, intermediate or long-range ordered crystalline phase was contained. This was done the crucible containing the cadmium is heated to a temperature of about 375 ° C.

Example 4

According to Example 1, a layer was applied to the substrate, which has a matrix of vitreous Cadmium and selenium, about 30% of which were dispersed, intermediate or long-range ordered crystalline phase existed. For this purpose, the substrate was heated to around 140.degree.

According to Example 1, a layer was applied to the substrate, which has a matrix of vitreous Cadmium and selenium possessed about 30% from a dispersed, intermediate or long-range ordered crystalline phase existed. Thereafter, the coated substrate was left for about 5 minutes heated to a temperature of about 120 ° C for a long time.

Example 6

According to the method according to Example 1, a 19 μm thick layer was applied to the substrate, which contained about 5% lead and 95% selenium.

^J 5 During the evaporation, the crucible containing the lead was kept at a temperature of about 803 ° C, while the crucible containing the selenium was kept at a temperature of 217 ° C. The evaporation ended in about 2 hours. X-ray diffraction showed a glass-like structure with no crystalline portions. The absorption edge of this material occurred at about 1.1 μm. Photosensitivity peaked at about 7,000 angstroms, with one third of the peak photosensitivity being observed at 8,000 angstroms. A stationary photoconductivity was observed beyond the absorption edge (about 1.2 μm). The absorption edge and the photoconductive edge were far from the corresponding edges for PbSe and Se. The conductivity of the vitreous lead-selenium material was between that of selenium and that of Pb-Se. The electronic properties of this vitreous material were markedly different from the properties of the components or a crystalline compound of the components.

Example 7

The semiconductor of Example 6 was manufactured according to the electrophotographic method of Example 2 charged, exposed and developed to produce a legible copy of an original image.

Example 8

According to Example 1, a 24 μm thick layer with about Produces 8% zinc and 92% selenium. During the evaporation of the components, the one containing the zinc became Crucible at a temperature of about 411 ° C and the crucible containing the selenium at about Maintained 217 ° C. The layer examined by X-ray diffraction showed no crystalline Structure. The photoconductivity edge extends approximately 700 angstroms compared to vitreous selenium towards longer wavelengths. Since the fundamental absorption edge of crystalline ZnSe at is about 4700 Angstroms, it becomes clear that the

advanced spectral sensitivity not on crystalline ZnSe is based.

Example 9

The product obtained in Example 8 was charged, exposed and developed according to Example 2, to create a readable copy of an original image.

Example 10

According to Example 1, a film was produced with about 25% cadmium and 75% selenium. During the evaporation step the crucible containing the cadmium was kept at a temperature of 356 ° C and the crucible containing the selenium was kept at a temperature of 217 ° C. An X-ray diffraction indicated the presence of a vitreous structure.

Example 11

According to Example 1, a layer with about 10% Zn and about 90% selenium was produced. The one containing the zinc The crucible was kept at a temperature of about 385 ° C and the crucible containing the selenium on one Maintained temperature of about 217 ° C. An X-ray diffraction showed that the layer was free from crystalline proportions.

Example 12

According to Example 1, a layer with about 20% bismuth and 80% selenium was produced. The bismuth The crucible containing the selenium was kept at a temperature of about 751 ° C and the crucible containing the selenium kept at a temperature of about 217 ° C. The vitreous layer thus formed was considered to be electrophotographic Infrared photoreceiver used by charging the layer according to Example 2, exposed and developed. By using filters that remove all visible light filtered away and only allowed radiation with a wavelength of more than 8200 Angstroms to pass through produces good images.

A number of other such selenium-bismuth layers were produced which were 10 to 30 µm thick and contained up to 30 atomic percent bismuth. Its vitreous character has been confirmed by X-ray and electron diffraction. Most of the electro-optical measurements were carried out on "sandwich" layers using gold and transparent electrodes. For the compositions examined, the dark conductivities (300 ° K) were between 10 ~ ⁶ ohms " ¹ cm" ¹ and <10 " ¹⁴ ohms" ¹ cm " ^1. A change of only about 5 atomic percent in the bismuth concentration shifted the maximum spectral sensitivity from 0 , 9ev to 1. 8ev. The band gaps derived from investigations of the spectral sensitivity corresponded to those obtained from a resistance temperature diagram.

Additional measurements of the μτ product and the decay time τ ₀ in the case of highly irradiated photon flows (no capture range) resulted in an effective microscopic mobility for a composition

of (μ _π + μ _ρ ) ~ 10 " ⁵ cm ² / volt-seconds. As an infrared detector material, Se-Bi D * values at a peak sensitivity wavelength (~ 1.1 μ) of up to 7 X 10" ¹⁰ cm / watt -Seconds ^m , which are advantageous compared to the values for PbS cells.

ίο There were response times in the range of 0.1 milliseconds measured up to 1 millisecond.

Example 13

According to Example 1, a layer with about 20% bismuth and 80% phosphorus was produced. The crucible containing the bismuth was maintained at a temperature of about 751 ° C and the crucible containing the phosphorus was maintained at about 187 ° C. This film showed a glass-like structure by X-ray diffraction .

Example 14

According to Example 1, a layer with about 15% zinc and 85% boron was produced. The one containing the zinc Crucible was at a temperature of about 385 ° C

and the crucible containing the boron is maintained at a temperature of about 2100 ° C. The boron was evaporated by electron bombardment. When examined by X-ray diffraction were no crystalline portions found.

Example 15

According to Example 1, a layer with 25% cadmium and 75% sulfur was produced. The the cadmium The crucible containing the sulfur was kept at a temperature of about 356 ° C Keep crucible at a temperature of about 100 ° C. For X-ray diffraction examinations a glass-like structure emerged.

Example 16

According to Example 1, a layer containing 10% zinc and 90% sulfur was produced. The that The crucible containing zinc was kept at a temperature of about 385 ° C and that containing the sulfur Keep the crucible at a temperature of about 100 ° C. When examined by X-ray diffraction, no crystalline portions were found.

The invention is not restricted to the above examples, since these are merely illustrative serve the method according to the invention.

1 sheet of drawings

Claims (5)

Patent claims: 1. Process for the production of a semiconducting layer, in which a binary semiconductor on a layer support is vapor-deposited, characterized in that a semiconductor-forming Metal and a semiconductor-forming non-metal which is solid under normal conditions evaporated at the same time and the vapors on a substrate kept at a temperature below the melting point of the expected semiconductor is held down. 2. The method according to claim 1, characterized in that the metal is cadmium, zinc, Gallium, lead, thallium, indium or bismuth and, as non-metals, boron, arsenic, carbon, phosphorus, Sulfur or preferably selenium is used. 3. The method according to claim 1, characterized in that after receiving the semiconducting Layer the vapor deposition at a temperature of the support which is above the melting point of the expected semiconductor lies, is continued until the amorphous semiconducting layer a crystalline layer is obtained. 4. The method according to claim 1, characterized in that after receiving the semiconducting Layer of substrate is heated above the melting point of the semiconductor until an amorphous and a crystalline semiconducting layer can be obtained on the support. 5. The method according to claim 1, characterized in that more metal than the stoichiometric Amount corresponds to the layer substrate is deposited.