GB2111534A - Making photoresponsive amorphous alloys and devices by reactive plasma sputtering - Google Patents

Abstract

A reactive plasma is formed between at least one solid phase material target (44) having one or more elements (Si) to be incorporated in the deposited alloy body and a substrate (28) spaced therefrom. The reactive plasma is formed from a gas including at least fluorine or a fluorine containing compound which etches the element(s) from the target which react with the fluorine and are deposited on the substrate with the fluorine. Other structural, compensating or altering elements can be added during the deposition, either simultaneously or sequentially. The deposition rate can be controlled by the introduction of oxygen into the plasma and removal rate of the element(s) can be controlled by the introduction of hydrogen. The deposition rate can be further controlled by varying the bias on the target. The deposits can be used as doped semi conductors for solar cells, photoelectric diodes and photocopying materials. <IMAGE>

Description

SPECIFICATION Chemical phase deposition process for making photoreponsive amorphous alloys and devices This invention relates to a method of making new and improved amorphous alloys by a new method of film deposition herein referred to as chemical phase deposition. According to a preferred method of the present invention a reactive plasma is formed with fluorine or a fluorine containing gas and allowed to interact with solid phase materials to incorporate the solid phase materials in the plasma. Advantageously the plasma results in the deposition of an alloy film with properties which reflect both the plasma and the solid phase materials to provide a solid state material having controlled and improved properties.Preferably other gases, such as hydrogen, can be independently introduced into the deposition environment to provide the controlled incorporation of the same in the deposited film. Advantageously the alloys have desired electrical and photoresponsive characteristics and can be used to form devices of many kinds including transistors, photovoltaic cells, photo sensors, photo copying materials, and diodes to name just a few. The invention has its most important application in making new and improved photoresponsive alloys of high purity and desired composition and devices made therefrom for various photoresponsive applications including photoreceptive devices such as solar cells of a p-i-n, p-n, Schottky or MIS (metal-insu lator-semiconductor) type; photoconducting medium such as utilized in xerography; photodetecting devices and photodiodes including large area photodiode arrays.

Silicon is the basis of the huge crystalline semiconductor industry and is the material which has produced expensive high efficiency (1 8 per cent) crystalline solar cells for space applications.

When crystalline semiconductor technology reached a commercial state, it became the foundation of the present huge semiconductor device manufacturing industry. This was due to the ability of the scientist to grow substantially defect-free germanium and particularly silicon crystals, and then turn them into extrinsic materials with p-type and n-type conductivity regions therein. This was accomplished by diffusing into such crystalline material parts per million of donor (n) or acceptor (p) dopant materials introduced as substitutional impurities into the substantially pure crystalline materials, to increase their electrical conductivity and to control their being either of a p or n conduction type. The fabrication processes for making p-n junction crystals involve extremely complex, time consuming, and expensive procedures.Thus, these crystalline materials useful in solar cells and current control devices are produced under very carefully controlled conditions by growing individual single silicon or germanium crystals, and when p-n junctions are required, by doping such single crystals with extremely small and critical amounts of dopants.

These crystal growing processes produce such relatively small crystals that solar cells require the assembly of many single crystals to encompass the desired area of only a single solar cell panel.

The amount of energy necessary to make a solar cell in this process, the limitation caused by the size limitations of the silicon crystal, and the necessity to cut up and assemble such a crystalline material have all resulted in an impossible economic barrier to the large scale use of crystalline semiconductor solar cells for energy conversion. Further, crystalline silicon has an indirect optical edge which results in poor light absorption in the material. Because of the poor light absorption, crystalline solar cells have to be at least 50 microns thick to absorb the incident sunlight. Even if the single crystal material is replaced by polycrystalline silicon with cheaper production processes, the indirect optical edge is still maintained; hence the material thickness is not reduced.The polycrystalline material also involves the addition of grain boundaries and other problem defects.

In summary, crystal silicon devices have fixed parameters which are not variable as desired, require large amounts of material, are only producible in relatively small areas and are expensive and time consuming to produce.

Devices based upon amorphous silicon alloys can eliminate these crystal silicon disadvantages.

Amorphous silicon alloys have an optical absorption edge having properties similar to a direct gap semiconductor and only a material thickness of one micron or less is necessary to absorb the same amount of sunlight as the 50 micron thick crystalline silicon. Further, amorphous silicon based alloys can be made faster, easier, with less energy, and in larger areas than can crystalline silicon.

Accordingly, a considerable effort has been made to develop processes for readily depositing amorphous semiconductor alloys or films, each of which can encompass relatively large areas, if desired, limited only by the size of the deposition equipment, and which could be readily doped to form p-type and n-type materials where p-n junction devices are to be made therefrom equivalent to those produced by their crystalline counterparts. For many years such work was substantially unproductive. Amorphous silicon or germanium (Group IV) films are normally four-fold coordinated and were found to have microvoids and dangling bonds and other defects which produce a high density of localized states in the energy gap thereof.The presence of a high density of localized states in the energy gap of amorphous silicon semiconductor films results in a low degree of photoconductivity and short carrier lifetime, making such films unsuitable for photoresponsive applications. Additionally, such films cannot be successfully doped or otherwise modified to shift the Fermi level close to the conduction or valence bands, making them unsuitable for making p-n junctions for solar cell and current control device applications.

In an attempt to minimize the aforementioned problems involved with amorphous silicon and germanium, W. E. Spear and P. G. Le Comber of Carnegie Laboratory of Physics, University of Dundee, in Dundee, Scotland, did some work on "Substitutional Doping of Amorphous Silicon", as reported in a paper published in Solid State Communications, Vol. 1 7, pp. 11 93-1196, 1975, toward the end of reducing the localized states in the energy gap in amorphous silicon or germanium to make the same approximate more closely intrinsic crystalline silicon or germanium and of substitutionally doping the amorphous materials with suitable classic dopants, as in doping crystalline materials, to make them extrinsic and of p or n conduction types.The reduction of the localized states was accomplished by glow discharge deposition of amorphous silicon films wherein a gas of silane (SiH4) was passed through a reaction tube where the gas was decomposed by an r.f. glow discharge and deposited on a substrate at a substrate temperature of about 500-6000K (227-3270C). The material so deposited on the substrate was an intrinsic amorphous material consisting of silicon and hydrogen. To produce a doped amorphous material a gas of phosphine (PH3) for n-type conduction or a gas of diborane (B2H6) for p-type conduction were premixed with the silane gas and passed through the glow discharge reaction tube under the same operating conditions. The gaseous concentration of the dopants used was between about 5 x 10-6 and 1 o6 parts per volume.The material so deposited included supposedly substitutional phosphorus or boron dopant and was shown to be extrinsic and of n or p conduction type.

While it was not known by these researchers, it is now known by the work of others that the hydrogen in the silane combines at an optimum temperature with many of the dangling bonds of the silicon during the glow discharge deposition, to substantially reduce the density of the localized states in the energy gap toward the end of making the electronic properties of the amorphous material approximate more nearly those of the corresponding crystalline material.

The incorporation of hydrogen in the above method not only has limitations based upon the fixed ratio of hydrogen to silicon in silane, but, most importantly, various Si:H bonding configurations introduce new antibonding states which can have deleterious consequences in these materials. Therefore, there are basic limitations in reducing the density of localized states in these materials which are particularly harmful in terms of effective p as well as n doping. The resulting density of states of the silane deposited materials leads to a narrow depletion width, which in turn limits the efficiencies of solar cells and other devices whose operation depends on the drift of free carriers. The method of making these materials by the use of only silicon and hydrogen also results in a high density of surface states which affects all the above parameters.

After the development of the glow discharge deposition of silicon from silane gas was carried out, work was done on the sputter depositing of amorphous silicon films in the atmosphere of a mixture of argon (required by the sputtering deposition process) and molecular hydrogen, to determine the results of such molecular hydrogen on the characteristics of the deposited amorphous silicon film. This research indicated that the hydrogen acted as an altering agent which bonded in such a way as to reduce the localized states in the energy gap. However, the degree to which the localized states in the energy gap were reduced in the sputter deposition process was much less than that achieved by the silane deposition process described above. The above described p and n dopant gases also were introduced in the sputtering process to produce p and n doped materials.These materials had a lower doping efficiency than the materials produced in the glow discharge process. Neither process produced efficient p-doped materials with sufficiently high acceptor concentrations for producing commercial p-n or p-i-n junction devices. The n-doping efficiency was below desirable acceptable commercial levels and the p-doping was particularly undesirable since it reduced the width of the band gap and increased the number of localized states in the band gap.

The prior deposition of amorphous silicon, which has been altered by hydrogen from the silane gas in an attempt to make it more closely resemble crystalline silicon and which has been doped in a manner like that of doping crystalline silicon, has characteristics which in all important respects are inferior to those of doped crystalline silicon. Thus, inadequate doping efficiencies and conductivity were achieved especially in the p-type material, and the photovoltaic qualities of these silicon films left much to be desired.

Greatly improved amorphous silicon alloys having significantly reduced concentrations of localized states in the energy gaps thereof and high quality electronic properties have been prepared by glow discharge as fully described in U.S. Patent No. 4,226,898, Amorphous Semiconductors Equivalent to Crystalline Semiconductors, Stanford R. Ovshinsky and Arum Madan which issued October 7, 1980, and by vapor deposition as fully described in U.S. Patent No. 4,217,374, Stanford R. Ovshinsky and Masatsugu Izu, which issued on August 12, 1980, under the same title. As disclosed in these patents, which are incorporated herein by reference, fluorine is introduced into the amorphous silicon semiconductor to substantially reduce the density of localized states therein.

Activated fluorine especially readily diffuses into and bonds to the amorphous silicon in the amorphous body to substantially decrease the density of localized defect states therein, because the small size, specificity, and high reactivity of the fluorine atoms enables them to be readily introduced into the amorphous body. The fluorine bonds to the dangling bonds of the silicon and forms what is believed to be a partially ionic stable bond with flexible bonding angles, which results in a more stable and more efficient compensation or alteration than is formed by hydrogen and other compensating or altering agents.Fluorine is considered to be a more efficient compensating or altering element than hydrogen when employed alone or with hydrogen because of its exceedingly small size, high reactivity, specificity in chemical bonding, and highest electronegativity, which is of particular importance because it is the most extremely electronegative element. Hence, fluorine is qualitatively different from other halogens and so is considered a super-halogen.

Fluorine also acts by its inductive effect to control the hydrogen bonding of these materials in a preferable manner.

As an example, compensation may be achieved with fluorine alone or in combination with hydrogen with the addition of these element(s) in very small quantities (e.g., fractions of one atomic percent). However, the amounts of fluorine and hydrogen most desirably used are much greater than such small percentages so as to form a silicon-hydrogen4luorine alloy. Such alloying amounts of fluorine and hydrogen may, for example, be in the range of 1 to 5 percent or greater. It is believed that the new alloy so formed has a lower density of defect states in the energy gap than that achieved by the mere neutralization of dangling bonds and similar defect states.Such larger amount of fluorine, in particular, is believed to participate substantially in a new structural configuration of an amorphous silicon-containing material and facilitates the addition of other alloying materials, such as germanium. Fluorine, in addition to its other characteristics mentioned herein, is believed to be an organizer of local structure in the silicon-containing alloy through inductive and ionic effects. It is believed that fluorine also influences the bonding of hydrogen by acting in a beneficial way to decrease the density of defect states which hydrogen contributes while acting as a density of states reducing element. The ionic role that fluorine plays in such an alloy is believed to be an important factor in terms of the nearest neighbor relationships.

Applicants herein have discovered a new and improved process for making amorphous semiconductor alloys containing at least fluorine to take advantage of all of the previously described superior characteristics of fluorine in such alloys. This new process, herein referred to as chemical phase deposition, facilitates the formation of new alloys having desired electrical and photoresponsive characteristics. Fluorine alone or other desired elements in addition to fluorine can be incorporated into the semiconductor alloy bodies in desired amounts without exposing the deposition conditions to deleterious impurities. Thus, not only new alloys can be formed, but also, alloys of very high purity.

One process somewhat related to the process of the present invention has been reported by E. Kay and A. Dilks in an article titled "Plasma Polymerization of Fluorocarbons in RF Capacitively Coupled Diode System", J. Vac. Sci. Technol., Vol.

18, No. 1, Jan.JFeb. 1981, pp. 1-1 1. This work dealt with the interrelationship between plasma etching and plasma polymerization with emphasis on the plasma-surface interaction leading to polymerization. Particular reference is made to the synthesis of metal containing fluoropolymers by simultaneous plasma etching and polymerization in the same system. However, the preparation of active semiconductor materials is not reported by these authors apparently due to the highly polymerized nature of the synthesized materials.

The material had long polymeric carbon-fluorine chains rendering such materials virtually useless for electronic applications.

Generally, the present invention relates to a method of making a solid phase alloy comprising forming a reactive plasma from fluorine gas between a substrate and at least one solid phase material target to cause the plasma to deposit a film of the alloy, the plasma containing at least one element which is to be incorporated in the alloy.

Accordingly the present invention provides a method of making a solid phase alloy, said method comprising forming a reactive plasma from fluorine gas between a substrate and at least one solid phase material target having at least one element to be incorporated in said alloy to cause said at least one element to be incorporated into said plasma and to cause said plasma to deposit a film of said alloy, said alloy having properties which are dependent upon both said plasma and said at least one element to provide a solid phase alloy material with controlled properties.

The present invention also relates to the manufacture of amorphous devices made from the alloys made by the method of the present invention.

In a preferred form of the invention, an electric field is formed between a solid phase material target having an element to be incorporated in the deposited alloy body on a substrate spaced from the target. A gas including at least fluorine or a fluorine containing compound is introduced between the substrate and target. A plasma is thereafter formed between the substrate and target for removing the element from the target.

The element is thereby deposited on the substrate to form the alloy body. Preferably, the element reacts with the fluorine in the plasma so that the element and the fluorine are deposited on the substrate to form the alloy body. The target can include one or a multiple number of elements such as, for example, silicon and the gas introduced between the substrate and target can be, for example, pure fluorine, because fluorine is an easily dissociatable gas which can result in reactive atoms of particular use. Other gases can be introduced with the fluorine to moderate the reactivity such as by their degree of inertness. For example, fluorine can be dissociated by an electric field created plasma or by ion beam of thermal dissociation as well.Because the materials introduced into the plasma reaction can be positively and accurately controlled by the composition of target or targets, alloy bodies of high purity can be formed.

Radical formation is an initial step; however, the length of time the radicals can survive, that is, their ability to avoid recombination depends upon the pressure of the gas. The distance the radicals must travel is very important and recombination processes, such as third body constituents and surfaces are available to facilitate recombination.

All of these must be taken into consideration in designing a desired alloy. The resulting amorphous materials made by this process can be extremely clean materials. The control of impurities and the ability to properly bond the constituent elements in ways not available by ordinary plasma decomposition (glow discharge) are important in this approach. The kinetics of the radical processes are affected by lifetime and recombination processes, and therefore diluent gases (which can be inert) can play an important role.

The amorphous alloy as a result incorporates at least one density of states reducing element, preferably fluorine. Other structural, compensating or altering elements can be added during deposition. To control the deposition rate, a first scavenging gas can be added in the plasma to scavenge the element to be incorporated in the alloy. In the case of a silicon based alloy, the first scavenging gas can be oxygen or other gasses to scavenge the silicon and reduce the deposition rate. Also, a second scavenging gas, such as hydrogen or an inert gas, may be added to scavenge the fluorine for reducing the fluorine etching of the target. The electric field between the target and the substrate can be either a unidirectional, RF, or audio frequency field and the bias between the target and substrate can be varied to control the deposition rate.The alloy has a substantially reduced number of states in the band gap because of the presence of fluorine in the alloy.

The presence of fluorine in the alloy of the invention provides an amorphous silicon alloy which differs physically, chemically and electrochemically from other amorphous silicon alloys, most notably amorphous silicon alloys compensated with hydrogen, because fluorine not only bonds to the silicon, but also effects in a positive manner the structural short range order of the material. This allows other elements such as altering or doping elements effectively to be added to the alloy, because fluorine forms stronger and more stable bonds than does hydrogen. Fluorine compensates or alters silicon more efficiently than hydrogen, because of the stronger more thermally stable bonds and more flexible bonding configurations due to the ionic nature of the fluorine bonding. Fluorine also has a stabilizing effect on the hydrogen bonding configurations and the resulting alloy.Because of the influence of fluorine, the new alloy maintains substantially high electronic qualities and photoconductivity and has excellent doping efficiency, and furthermore, possesses better structural stability for photovoltaic energy conversion applications.

Hydrogen further enhances the fluorine compensated or altered alloy and can be added during deposition with fluorine or after deposition.

as can fluorine and other alterant elements. The post deposition incorporation of hydrogen is advantageous when it is desired to utilize the higher deposition substrate temperature allowed by fluorine.

The present invention further provides a method of making an alloy by chemical phase deposition comprising forming an electric field between at least one solid phase material target which has at least one element to be incorporated in the deposited alloy and a substrate spaced apart therefrom, introducing a gas including at least fluorine or a fluorine containing compound between the substrate and the target, and forming a plasma between the substrate and target for etching the element to be incorporated in the deposited alloy body from the target and thereby deposit at least that element on the substrate to form the alloy body.

An embodiment of the invention will now be described by way of example, with reference to the drawings accompanying this specification in which: Fig. 1 is a diagrammatic representation of a chemical phase deposition system for making the amorphous alloy bodies in accordance with the present invention; Fig. 2 is a sectional view of a portion of the system of Fig. 1 taken along the line 2-2 therein; Fig. 3 is a diagrammatic representation, similar to Fig. 1, of a chemical phase deposition system having a plurality of targets with corresponding shutters for incorporating a plurality of elements into the alloy bodies either simultaneously or sequentially; Fig. 4 illustrates an application wherein the deposition of the amorphous alloy and the application of the activated fluorine and hydrogen may be carried out as separate steps and in separate enclosures; ; Fig. 5 illustrates exemplary apparatus for diffusing activated hydrogen into a previously deposited amorphous alloy; Fig. 6 is a fragmentary sectional view of an embodiment of a Schottky barrier solar cell to illustrate one application of the amorphous semiconductor photoreceptive alloys made by the process of the invention; Fig. 7 is a fragmentary sectional view of a p-n junction solar cell device which includes a doped amorphous semiconductor alloy made by the process of the invention; Fig. 8 is a fragmentary sectional view of a photo-detection device which includes an amorphous semiconductor alloy made by the process of the invention; Fig. 9 is a fragmentary sectional view of a xerographic drum including an amorphous semiconductor alloy made by the process of the invention; Fig. 10 is a fragmentary sectional view of a p-i-n junction solar cell device;; Fig. 11 is a fragmentary sectional view of an n-i-p junction solar cell device.

Referring now more particularly to Fig. 1, there is shown a chemical phase deposition system 10 including a housing 12. The housing 12 encloses a vacuum chamber 14 and includes an inlet chamber 16 and an outlet chamber 18. A cathode backing member 20 is mounted in the vacuum chamber 11 through an insulator 22.

The backing member 20 includes an insulating sleeve 24 circumferentially enclosing the backing member 20. A dark space shield 26 is spaced from and circumferentially surrounds the sleeve 24. A substrate 28 is secured to an inner end 30 of the backing member 20 by a holder 32. The holder 32 can be screwed or otherwise conventionally secured to the backing member 20 in electrical contact therewith.

The cathode backing member 20 includes a well 34 into which is inserted an electrical heater 36 for heating the backing member 20 and hence the substrate 28. The cathode backing member 20 also includes a temperature responsive probe 38 for measuring the temperature of the backing member 20. The temperature probe 38 is utilized to control the energization of the heater 36 to maintain the backing member 20 and the substrate 28 at any desired temperature.

The system 10 also includes an electrode 40 which extends from the housing 12 into the vacuum chamber 14 spaced from the cathode backing member 20. The electrode 40 includes a shield 42 surrounding the electrode 40 and which in turn carries a target 44 mounted thereon. The electrode 40 includes a well 46 into which is inserted an electrode heater 48. The electrode 40 also includes a temperature responsive probe 50 for measuring the temperature of the electrode 40 and hence the target 44. The probe 50 is utilized to control the energization of the heater 48 to maintain the electrode 40 and the target 44 at any desired temperature, independently of the member 20.

A plasma is developed in a space 52 between the substrates 28 and target 44 by the power generated from a regulated R.F., audio frequency or unidirectional power source coupled to the cathode backing member 20 across the space 52 to the electrode 40 which is coupled to a biasing control 53. The vacuum chamber 14 is evacuated to the desired pressure by a vacuum pump 54 coupled to the chamber 14 through a particle trap 56. A pressure gauge 58 is coupled to the vacuum system and is utilized to control the pump 54 to maintain the system 10 at the desired pressure.

The inlet chamber 1 6 of the housing 12 preferably is provided with a plurality of conduits 60 for introducing materials into the system 10 to be mixed therein and to be deposited in the chamber 14 in the plasma space 52 upon the substrate 28. If desired, the inlet chamber 16 can be located at a remote location and the gases can be premixed prior to being fed into the chamber 14. The gaseous materials are fed into the conduits 60 through a filter or other purifying device 62 at a rate controlled by a valve 64.

When a material initially is not in a gaseous form, but instead is in a liqud or solid form, it can be placed into a sealed container 66 as indicated at 68. The material 68 then is heated by a heater 70 to increase the vapor pressure thereof in the container 66. A suitable gas, such as argon, is fed through a dip tube 72 into the material 68 so as to entrap the vapors of the material 68 and convey the vapors through a filter 62' and a valve 64' into the conduits 60 and hence into the system 10.

The inlet chamber 16 and the outlet chamber 18 preferably are provided with screen means 74 to confine the plasma in the chamber 14 and principally between the substrate 28 and target 44.

The gas materials fed through the conduits 60 are mixed in the inlet chamber 16 and then introduced or fed into the space 52 to maintain the plasma. The alloy body deposited on the substrate can incorporate silicon, fluorine, oxygen and the other desired alterant elements, such as hydrogen, and/or dopants or other desired materials.

In operation, and by way of a first example for making an intrinsic amorphous silicon alloy, the target 44, comprising elemental silicon is first placed onto the shield 42. An R.F., unidirectional or audio frequency field is then formed between the substrate 28 and the target 44. The system 10 is then pumped down to a desired deposition pressure, such as less than 60 mtorr. Fluorine gas is then fed into the inlet chamber 16 through one of the conduits 60 and then introduced into the space 52. A reactive plasma of the fluorine is then formed in the space 52. The plasma causes the fluorine gas to form charged free radicals or ions by the reaction; F + e~ e F-. The negatively charged fluorine ions bombard the silicon target 44 to etch silicon from the target.The etched silicon then reacts with the fluorine and the same are deposited as an intrinsic amorphous siliconfluorine alloy body on the substrate 28. Hydrogen can be independently introduced into the deposition environment through one of the conduits 60. In this manner, a controlled amount of hydrogen can also be incorporated into the film as desired.

As another example, the intrinsic amorphous silicon alloy body can be formed by using silicon tetrafluoride gas instead of pure fluorine gas.

Again negatively charged free fluorine radicals will be produced in the plasma to etch the silicon from the target. Here, the fluorine will not only react with the removed silicon but also the silicon resulting from the disassociation of the siliconfluorine bonds of the gas. As a result, an intrinsic amorphous silicon-fluorine alloy body will be deposited on the substrate.

Radical formation is an initial step. However, the length of time the radicals can survive and avoid recombination depends upon the pressure of the gas. The distance the radicals must travel is very important and recombination processes, such as, third body constituents and surfaces are available to facilitate recombination. All of these must be taken into consideration in designing a desired alloy. The resulting amorphous materials made by this process can be extremely clean due to control of impurities and the ability to properly bond the constituent elements which may not be available by ordinary plasma decomposition (glow discharge). Since the kinetics of the radical processes are affected by lifetime and recombination processes, diluent gases (which can be inert) can play an important role.

For either example, if it is desired to decrease the deposition rate, a first scavenging gas such as oxygen or other gasses can be introduced into the space 52. The oxygen will scavenge a portion of the silicon and thus reduce the rate in which the silicon alloy is deposited. The deposition rate also can be varied by varying the biasing between the target 44 and the substrate 28 with the bias control 53. Additionally, if it is desired to reduce the fluorine etching or removal of the silicon from the target 44, a second scavenging gas such as hydrogen gas can also be introduced into the space 52. The hydrogen will form relatively stable HF bonds with the fluorine and thus reduce the amount of free fluorine available for bombarding the silicon target.

To form a wide band gap p-doped amorphous silicon alloy, the target can be powdered boron, aluminum, gallium, indium or thallium held within a boat to replace the target 44. The reaction gases can be silicon tetrafluoride and carbon tetrafluoride, nitrogen, or ammonia gas (NH3).

Hydrogen gas also can be optionally used to control the fluorine etching and as an additional compensating element. The carbon or nitrogen serves to increase or alter the band gap of the silicon and the boron removed from the target substitutionally dopes the amorphous silicon to form a p-type alloy.

This last example clearly shows how flexible the process of the invention is. Traditionally, diborane (B2H6) has been used as a p-type dopant gas. The boron and hydrogen have a fixed ratio. By virtue of the present invention, the deposition is not tied to any fixed ratio. Any amount of boron with hydrogen can be incorporated into the alloy body.

To form an n-type amorphous silicon alloy body, the target can be powdered phosphorus, arsenic, antimony, or bismuth in a boat and the fluorine containing reaction gas can be silicon tetrafluoride. Again, hydrogen and/or other gasses can also be used to control deposition and etching rates. The dopants also can be incorporated in the target or targets 44.

The system of Fig. 1 and the process of the present invention can also be utilized to form a narrow band gap intrinsic amorphous silicon alloy body. As disclosed in U.S. Patent No. 4,342,044 issued July 27, 1 982, in the names of Stanford R.

Ovshinsky and Masatsugu Izu and titled "Method for Optimizing Photoresponsive Amorphous Alloys and Devices", germanium or tin can be incorporated into an amorphous silicon-fluorine alloy to decrease or adjust the band gap of the alloy to optimize the same. The germanium or tin can be incorporated into the alloy without increasing the density of states in the band gap thereof due to the presence of fluorine in the alloy.

Here, such an alloy can be made by using a target of tin, lead, or powdered germanium in a boat and introducing silicon tetrafluoride into the space 52. Again, as in the case of each preceding example, hydrogen and/or other gasses can be introduced into the plasma to control the etching and deposition rates, respectively. Also, by varying the biasing on the target, the amount of germanium, lead, or tin incorporated into the film can be selectively varied to grade the band gap of the resulting alloy body.

Referring now to Fig. 3, the apparatus there illustrated is substantially identical to the apparatus of Fig. 1. As a result, reference characters are repeated to indicate corresponding like elements.

In addition to the structure of Fig. 3 previously described with respect to Fig. 1 , the system of Fig. 3 further includes a pair of targets 44a and 44b and a corresponding number of shutters 45a and 45b, respectively. As will be appreciated, any number of targets and corresponding shutters can be provided. Each target 44a and 44b comprises a boat 47a and 47b and a solid phase material 49a and 49b contained therein each of which includes at least one element to be incorporated in an alloy body to be deposited on the substrate 28.

The shutters 45a and 45b when closed as illustrated, preclude the bombardment of the target materials 49a and 49b by the free fluorine negatively charged ions. Hence, the materials in this condition are not etched or removed and thus not incorporated into the alloy body to be deposited on the substrate 28.

When a shutter is opened, the solid phase material in its corresponding boat will be exposed to the fluorine and hence will be etched to react with the fluorine and be incorporated into the deposited alloy body. If both shutters 45a and 45b are opened, the at least one element of the solid phase materials contained therein will be simultaneously removed and incorporated into the deposited alloy body. Sequential opening and closing of the shutters 45a and 45b will result in sequential incorporation of the elements into the deposited alloy bodies to provide different alloy compositions. Hence, new alloy bodies of substantially unrestricted composition can be prepared by the process of the present invention.

As an example of the foregoing, a wide band gap p-type alloy can be made by placing powdered boron in one boat and carbon in the other boat. Both shutters are opened and then silicon tetrafluoride (SiF4) gas is introduced into space 52. As in the previous examples, fluorine will be disassociated from the silicon to form negatively charged radicals to etch and remove boron and carbon from the boats. As a result, the silicon, fluorine, boron, and carbon will react in the plasma and be deposited as an amorphous siliconfluorine-boron-carbon alloy body on the substrate 28 to form the wide band gap p-type amorphous alloy. Other band gap increasing elements may also be used in place of boron in powdered form including aluminum, gallium, indium, or thallium.

As another example, the narrow band gap intrinsic alloy can be prepared by placing solid phase silicon in one boat, powdered germanium, tin, or lead in the other boat, and using fluorine or silicon tetrafluoride gas in the plasma. If it is desired to incorporate more than one of these elements into the alloy body, additional boats can also be utilized. The foregoing merely illustrates that many different combinations of materials can be utilized in practicing the present invention and that alloys of virtually limitless different compositions can be prepared.

There are two different mechanisms by which the elements of the target can be removed for incorporation into the deposited alloy. The first mechanism as previously mentioned is by the fluorine etching the target materials. The second mechanism is by sputtering. The fluorine can, depending upon deposition parameters such as power or biasing, bombard the targets with such high momentum that the target materials are sputtered onto the substrate. Either mechanism can be utilized independently or in combination depending on the desired deposition rate or structural characteristics of the prepared alloy bodies. For example, if it is desired to enhance the etching mechanism, the bias can be made more positive. Conversely, if it is desired to enhance the sputtering mechanism, the bias can be made more negative when using a gas such as argon in place of fluorine.

As previously mentioned, the process of the present invention results in alloys of very high purity. The purity of the prepared amorphous silicon alloys can be further enhanced by coating the internal surfaces of the deposition chamber with silicon. This can be accomplished by sputtering silicon placed in one of the boats.

Oxides of constituent elements can also be deposited on the substrate 28 by the process of the present invention. Such oxides are particularly useful, for example, in Schottky barrier photovoltaic cells as enhancement layers and certain oxides are also useful as antireflection layers. Oxides of tin, germanium, silicon or most any other constituent element may be deposited by using the oxides as a solid phase target or by using the constituent element as the target and introducing oxygen or a gas along with the fluorine or fluorine containing compound gas into the plasma. Although the presence of oxygen may reduce the deposition rate, only very thin oxide layers are usually required.

As previously indicated, although it is preferred that the compensating and other elements be incorporated into the amorphous alloy as it is deposited, in accordance with another aspect of the invention, the amorphous alloy deposition process and the process of injecting the compensating and other agents into the semiconductor alloy can be done in a completely separate environment from the depositing of the amorphous alloy. This can have an advantage in certain applications since the conditions for injecting such agents are then completely independent of the conditions for the alloy deposition. Also, as previously explained, if the deposition process produces a porous alloy, the porosity of the alloy, in some cases, is more easily reduced by environmental conditions quite different from that present in the deposition process.To this end, reference should now be made to Figs. 4 and 5 which illustrate that the amorphous deposition process and the compensating or latering agent diffusion process are carried out as separate steps in completely different environments, Fig. 5 illustrating apparatus for carrying out the post compensation diffusion process.

As there shown, a low pressure container body 100 is provided which has a low pressure chamber 102 having an opening 104 at the top thereof. This opening 104 is closed by a cap 106 having threads 108 which thread around a corresponding threaded portion on the exterior of the container body 100. A sealing O-ring 110 is sandwiched between the cap 106 and the upper face of the container body. A sample-holding electrode 1 12 is mounted on an insulating bottom wall 1 14 of the chamber 100. A substrate 11 6 upon which an amorphous semiconductor alloy 11 8 has already been deposited is placed on the electrode 112. The upper face of the substrate 11 6 contains the amorphous alloy 118 to be altered or compensated in the manner now to be described.

Spaced above the substrate 11 6 is an electrode 120. The electrodes 1 12 and 120 are connected by cables 122 and 124 to a DC or RF supply source 126 which supplies a voltage between the electrodes 112 and 120 to provide an activated plasma of the compensating or altering gas or gasses, such as fluorine, hydrogen, and the like, fed into the chamber 102. For purposes of simplicity, Fig. 5 illustrates only molecular hydrogen being fed into the chamber 102 by an inlet conduit 128 passing through the cap 106 and extending from a supply tank 130 of molecular hydrogen. Other compensating or altering gasses (such as fluorine and the like) also may be similarly fed into the chamber 102. The conduit 128 is shown connected to a valve 132 near the tank 130. A flow rate indicating gauge 134 is shown connected to the inlet conduit 128 beyond the valve 132.

Suitable means are provided for heating the interior of the chamber 102 so that the substrate temperature is elevated preferably to a temperature below, but near the crystallization temperature of the film 118. For example, coils of heating wire 136 are shown in the bottom wall 114 of the chamber 102 to which coils connect a cable (not shown) passing through the walls of the container body 100 to a source of current for heating the same.

The high temperature together with a plasma of gas containing one or more compensating elements developed between the electrodes 11 2 and 120 achieve a reduction of the localized states in the band gap of the alloy. The compensating or altering of the amorphous alloy 118 may be enhanced by irradiating the amorphous alloy 11 8 with radiant energy from an ultraviolet light source 138, which is shown outside of the container body 100 directing ultraviolet light between the electrodes 112 and 120 through a quartz window 140 mounted in the side wall of the container body 100.

The low pressure or vacuum in the chamber 102 can be developed by a vacuum pump (not shown) such as the pump 56 in Fig. 1. The pressure of the chamber 102 can be on the order of .3 to 2 Torr with a substrate temperature on the order of 200 to 4500 C. The activated fluorine (and hydrogen) as well as other compensating or altering elements also can be produced from compounds containing the elements instead of from a molecular gas source, as previously mentioned.

Various applications of the improved amorphous alloys produced by the unique processes of the invention are illustrated in Figs. 6 through 11. Fig. 6 shows a Schottky barrier solar cell 142 in fragmentary cross-section. The solar cell 142 includes a substrate or electrode 144 of a material having good electrical conductivity properties, and the ability of making an ohmic contact with an amorphous alloy 146 compensated or altered to provide a low density of localized states in the energy gap.The substrate 144 may comprise a low work function metal, such as aluminum, tantalum, stainless steel or other material matching with the amorphous alloy 146 deposited thereon which preferably includes silicon, compensated or altered in the manner of the alloys previously described so that it has a low density of localized states in the energy gap of preferably no more than 1016 per cubic centimeter per eV. It is most preferred that the alloy have a region 148 next to the electrode 144, which region forms an n-plus conductivity, heavily doped, low resistance interface between the electrode and an undoped relatively high dark resistance region 150 which is an intrinsic, but low n-conductivity region.

The upper surface of the amorphous alloy 146 as viewed in Fig. 6, joins a metallic region 152, an interface between this metallic region and the amorphous alloy 146 forming a Schottky barrier 154. The metallic region 152 is transparent or semi-transparent to solar radiation, has good electrical conductivity and is of a high work function (for example, 4.5 eV or greater, produced, for example, by gold, platinum, palladium, etc.) relative to that of the amorphous alloy 146. The metallic region 152 may be a single layer of a metal or it may be a multi-layer. The amorphous alloy 146 may have a thickness of about .5 to 1 micron and the metallic region 152 may have a thickness of about 100 A in order to be semitransparent to solar radiation.

On the surface of the metallic region 152 is deposited a grid electrode 156 made of a metal having good electrical conductivity. The grid may comprise orthogonally related lines of conductive material occupying only a minor portion of the area of the metallic region, the rest of which is to be exposed to solar energy. For example, the grid 1 56 may occupy only about from 5 to 10% of the entire area of the metallic region 1 52. The grid electrode 156 uniformly collects current from the metallic region 152 to assure a good low series resistance for the device.

An anti-reflection layer 158 may be applied over the grid electrode 1 56 and the areas of the metallic region 152 between the grid electrode areas. The anti-reflection layer 158 has a solar radiation incident surface 160 upon which impinges the solar radiation. For example, the anti-reflection layer 158 may have a thickness on the order of magnitude of the wavelength of the maximum energy point of the solar radiation spectrum, divided by four times the index of refraction of the anti-reflection layer 1 58. If the metallic region 152 is platinum of 100 A in thickness, a suitable anti-reflection layer 158 would be zirconium oxide of about 500 A in thickness with an index of refraction of 2.1.

The Schottky barrier 154 formed at the interface between the regions 150 and 152 enables the photons from the solar radiation to produce current carriers in the alloy 146, which are collected as current by the grid electrode 156.

An oxide layer (not shown) can be added between the layers 150 and 152 to produce an MIS (metal insulator semiconductor) solar cell.

In addition to the Schottky barrier or MIS solar cell shown in Fig. 6, there are solar cell constructions which utilize p-n junctions in the body of the amorphous alloy forming a part thereof formed in accordance with successive deposition, compensating or altering and doping steps like that previously described. These other forms of solar cells are generically illustrated in Fig. 7 as well as in Figs. and 11.

These constructions generally include a transparent electrode 164 through which the solar radiation energy penetrates into the body of the solar cell involved. Between this transparent electrode and an opposite electrode 166 is a deposited amorphous alloy 168 formed in accordance with the invention, preferably including silicon, initially compensated in the manner previously described. In this amorphous alloy 168 are at least two adjacent regions 170 and 172 where the amorphous alloy has respectively oppositely doped regions, region 170 being shown as a n-conductivity region and region 172 being shown as a p-conductivity region.The doping of the regions 170 and 1 72 is only sufficient to move the Fermi levels to the valence and conduction bands involved so that the dark conductivity remains at a low value achieved by the band adjusting and compensating or altering method of the invention. The alloy 1 68 has high conductivity, highly doped ohmic contact interface regions 174 and 176 of the same conductivity type as the adjacent region of the alloy 168. The alloy regions 174 and 176 contact electrodes 164 and 166, respectively.

Referring now to Fig. 8, there is illustrated another application of an amorphous alloy utilized in a photo-detector device 178 whose resistance varies with the amount of light impinging thereon.

An amorphous alloy 180 thereof is compensated or altered in accordance with the invention, has no p-n junctions are in the embodiment shown in Fig. 7 and is located between a transparent electrode 182 and a substrate electrode 184. In a photo-detector device it is desirable to have a minimum dark conductivity and so the amorphous alloy 180 has an undoped, but compensated or altered region 186 and heavily doped regions 188 and 190 of the same conductivity type forming a low resistance ohmic contact with the electrodes 182 and 1 84, which may form a substrate for the alloy 180.

Referring to Fig. 9 an electrostatic image producing device 192 (like a xerography drum) is illustrated. The device 192 has a low dark conductivity, selective wavelength threshold, undoped or slightly p-doped amorphous alloy 194 deposited on a suitable substrate 196 such as a drum.

As used herein, the terms compensating agents or materials and altering agents, elements or materials mean materials which are incorporated in the amorphous alloy for altering or changing the structure thereof, such as, activated fluorine (and hydrogen) incorporated in the amorphous alloy containing silicon to form an amorphous silicon/fluorine/hydrogen composition alloy, having a low density of localized states in the energy gap. The activated fluorine (and hydrogen) is bonded to the silicon in the alloy and reduces the density of localized states therein and due to the small size of the fluorine and hydrogen atoms they are both readily introduced into the amorphous alloy without substantial dislocation of the silicon atoms and their relationships in the amorphous alloy.This is true most particularly because of the extreme electronegativity, specificity and reactivity of fluorine, all of which characteristics organize the local chemical order of the alloys through the inductive powers of fluorine. The ability of fluorine to bond with both silicon and hydrogen results in the formation of alloys with a minimum of localized defect states in the energy gap.

Referring now to Fig. 10, a p-i-n solar cell 198 is illustrated having a substrate 200 which may be glass or a flexible web formed from stainless steel or aluminum. The substrate 200 is of a width and length as desired and preferably at least 3 mils thick. The substrate has an insulating layer 202 deposited thereon by the process of the present invention or by a conventional process such as chemical deposition, vapor deposition or anodizing in the case of an aluminum substrate. The layer 202 for instance, about 5 microns thick can be made of a metal oxide. For an aluminum substrate, it preferably is aluminum oxide (Al203) and for a stainless steel substrate it may be silicon dioxide (SiO2) or other suitable glass.

An electrode 204 is deposited in one or more layers upon the layer 202 to form a base electrode for the cell 198. The electrode 204 layer or layers is deposited by vapor deposition, which is a relatively fast deposition process. The electrode layers preferably are reflective metal electrodes of molybdenum, aluminum, chrome or stainless steel for a solar cell or a photovoltaic device. The reflective electrode is preferable since, in a solar cell, non-absorbed light which passes through the semiconductor alloy is reflected from the electrode layers 204 where it again passes through the semiconductor alloy which then absorbs more of the light energy to increase the device efficiency.

The substrate 200 is then placed in the deposition environment. The specific examples shown in Figs. 10 and 11 are illustrative of some p-i-n junction devices which can be manufactured utilizing the improved methods and materials of the invention. Each of the devices illustrated in Figs. 10 and 11, has an alloy body having an overall thickness of between about 3,000 and 30,000 angstroms. This thickness ensures that there are no pin holes or other physical defects in the structure and that there is maximum light absorption efficiency.A thicker material may absorb more light, but at some thickness will not generate more current since the greater thickness allows more recombination of the light generated electron-hole pairs. (It should be understood that the thicknesses of the various layers shown in Figs. 6 through 11 are not drawn to scale.) Referring first to forming the n-i-p device 198, the device is formed by first depositing a heavily doped n+ alloy layer 206 on the electrode 204.

Once the n+ layer 206 is deposited, an intrinsic (i) alloy layer 208 is deposited thereon. The intrinsic layer 208 is followed by a highly doped conductive p+ alloy layer 210 deposited as the final semiconductor layer. The amorphous alloy layers 206, 208 and 210 form the active layers of the n-i-p device 198.

While each of the devices illustrated in Figs. 10 and 11 may have other utilities, they will be now described as photovoltaic devices. Utilized as a 'photovoltaic device, the selected outer, p+ layer 210 is a low light absorption, high conductivity alloy layer. The intrinsic alloy layer 208 preferably has an adjusted wavelength threshold for a solar photoresponse, high light absorption, low dark conductivity and high photoconductivity. The bottom alloy layer 204 is a low light absorption, high conductivity n+ layer. The overall device thickness between the inner surface of the electrode layer 206 and the top surface of the p+ layer 210 is, as stated previously, on the order of at least about 3,000 angstroms. The thickness of the n+ doped layer 206 is preferably in the range of about 50 to 500 angstroms.The thickness of the amorphous intrinsic alloy 208 is preferably between about 3,000 angstroms to 30,000 angstroms. The thickness of the top p+ contact layer 210 also is preferably between about 50 to 500 angstroms. Due to the shorter diffusion length of the holes, the p+ layer generally will be as thin as possible on the order of 50 to 150 angstroms. Further, the outer layer (here p+ layer 210) whether n+ or p+ will be kept as thin as possible to avoid absorption of light in that contact layer.

A second type of p-i-n junction device 212 is illustrated in Fig. 11. In this device a first p+ layer 214 is deposited on the electrode layer 204' followed by an intrinsic amorphous alloy layer 216, an n amorphous alloy layer 218 and an outer n+ amorphous alloy layer 220. Further, although the intrinsic alloy layer 208 or 216 (in Figs. 10 and 11) is an amorphous alloy the other layers are not so restricted and could, for instance, be polycrystalline, such as layer 214. (The inverse of the Figs. 10 and 11 structure not illustrated, also can be utilized.) Following the deposition of the various semiconductor alloy layers in the desired order for the devices 198 and 212, a further deposition step is performed, preferably in the same deposition environment.In this step, a TCO layer 222 (transparent conductive oxide) is added which, for example, may be indium tin oxide (ITO), cadmium stannate (Cd2SnO4), or doped tin oxide (SnO2). The TCO layer will be added following the post compensation of fluorine (and hydrogen) if the films were not deposited with one or more of the desired compensating or altering elements therein. Also, the other compensating or altering elements, above described, can be added by post compensation.

An electrode grid 224 can be added to either of the devices 198 or 212 if desired. For a device having a sufficiently small area, the TCO layer 222 is generally sufficiently conductive such that the grid 224 is not necessary for good device efficiency. If the device is of a sufficiently large area or if the conductivity of the TCO layer 222 is insufficient, the grid 224 can be placed on the layer 222 to shorten the carrier path and increase the conduction efficiency of the devices.

Each of the device semiconductor alloy layers can be deposited upon the base electrode substrate by the process of the present invention and within the same chamber. It is only necessary to introduce the appropriate fluorine containing gas and other gases and open the shutters as previously described in serial relation to form the alloy layers of proper conductivity and thickness.

The semiconductor material is deposited onto the substrate which is heated to the desired deposition temperature for each alloy layer. The doped layers of the devices are deposited at various temperatures in the range of 2000C to about 1000 C, depending upon the form of the material used. The upper limitation on the substrate temperature in part is due to the type of metal substrate utilized. For aluminum the upper temperature should not be above about 6000C and for stainless steel it could be above about 10000 C.

The doping concentrations are varied to produce the desired p, p+, n or n+ type conductivity as the alloy layers are deposited for each device. For n or p doped layers, the material is doped with 5 to 100 ppm of dopant material as it is deposited. For n+ or p+ doped layers the material is doped with 100 ppm to over 1 per cent of dopant material as it is deposited.

As previously mentioned, the alloy layers other than the intrinsic alloy layer can be other than the amorphous layers, such as polycrystalline layers.

(By the term "amorphous" is meant an alloy or material which has long range disorder, although it may have short or intermediate order or even contain at times some crystalline inclusions.) Modifications and variations of the present invention are possible in light of the above teachings. It is therefore, to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.

Claims (62)

1. A method of making a solid phase alloy, said method comprising forming a reactive plasma from fluorine gas between a substrate and at least one solid phase material target having at least one element to be incorporated in said alloy to cause said at least one element to be incorporated into said plasma and to cause said plasma to deposit a film of said alloy, said alloy having properties which are dependent upon both said plasma and said at least one element to provide a solid phase alloy material within controlled properties.

2. The method according to claim 1 further comprising the step of introducing hydrogen gas between said substrate and said solid phase material target.

3. A method of making an alloy by chemical phase deposition, said method comprising: forming an electric field between at least one solid phase material target having at least one element to be incorporated in a deposited alloy body and a substrate spaced therefrom; introducing a gas, including at least fluorine or a fluorine containing compound, between said substrate and target; forming a plasma between said substrate and target for etching said at least one element from at least one target and to thereby deposit at least said element on said substrate to form said alloy body.

4. The method according to claim 3 wherein said at least one element is silicon.

5. The method according to any one of claims 3 or 4 wherein said solid phase material target includes at least one of the group consisting of germanium, tin, or lead.

6. The method according to any one of claims 3 or 4 wherein said solid phase material target includes at least one of the group consisting of boron, aluminum, gallium, indium, or thallium.

7. The method according to any one of claims 3 or 4 wherein said solid phase material target includes at least carbon.

8. The method according to any one of claims 3 or 4 wherein said solid phase material target includes at least one of the group consisting of phosphorus, arsenic, antimony, or bismuth.

9. The method according to any one of claims 3 to 8 wherein said gas is fluorine gas.

10. The method according to any one of claims 3 to 8 wherein said gas is silicon tetrafluoride gas.

11. The method according to any one of claims 3 to 8 wherein said electric field is an RF, unidirectional or audio frequency electric field.

12. The method according to any one of claims 3 or 4 wherein said solid phase material target includes at least silicon and wherein said gas is fluorine gas.

13. The method according to any one of claims 3 or 4 wherein said solid phase material target includes at least silicon and wherein said gas is silicon tetrafluoride gas.

14. The method according to any one of claims 3 or 4 wherein said solid phase material target includes at least boron and wherein said gas is silicon tetrafluoride gas.

1 5. The method according to any one of claims 3 or 4 wherein said solid phase material target includes at least carbon and wherein said gas is silicon tetrafluoride gas.

16. The method according to any one of claims 3 or 4 wherein said solid phase material target includes at least germanium and wherein said gas is silicon tetrafluoride gas.

17. The method according to any one of claims 3 or 4 wherein said solid phase material target includes at least tin and wherein said gas is silicon tetrafluoride.

18. The method according to any one of claims 3 or 4 wherein said solid phase material target includes at least phosphorus and wherein said gas is silicon tetrafluoride gas.

19. The method according to any one of claims 3 to 18 further comprising the step of introducing a first scavenging gas between said substrate and target for reducing the rate of deposition of said alloy body on said substrate.

20. The method according to claim 19 wherein said first scavenging gas is oxygen.

21. The method according to any one of claims 19 or 20 further comprising the step of introducing a second scavenging gas between said substrate and target for reducing the rate of removal of said at least one element from said target.

22. The method according to claim 21 wherein said second scavenging gas is hydrogen.

23. The method according to any one of claims 3 to 22 further comprising the step of establishing a bias voltage between said substrate and target and varying said bias voltage for controlling the rate in which said at least one element is incorporated in said deposited alloy body.

24. The method according to any one of claims 3 to 23 further comprising the step of providing a plurality of solid phase material targets, each of said targets having at least one element to be incorporated into said deposited alloy body.

25. The method according to claim 24 further comprising the step of sequentially exposing certain ones of said plurality of targets to said plasma for depositing an alloy body on said substrate having a layered structure of different compositions.

26. The method according to any one of claims 24 or 25 wherein said solid phase material targets include carbon and at least one of the group consisting of boron, aluminum, indium, or thallium, and wherein said gas is silicon tetrafluoride gas.

27. The method according to any one of claims 24 or 25 wherein said solid phase material targets include silicon and at least one of the group consisting of germanium, tin, or lead and wherein said gas is fluorine gas or silicon tetrafluoride gas.

28. The method according to any one of claims 24. 25 or 27 wherein said solid phase material targets include at least silicon, germanium, and tin, and wherein said gas is fluorine gas or silicon tetrafluoride.

29. The method according to any one of claims 3 to 28 wherein said solid phase material target includes the oxide of said at least one element.

30. An amorphous alloy made according to the process of claim 3.

31. An amorphous alloy made according to the process of claim 4.

32. An amorphous alloy made according to the process of claim 5.

33. An amorphous alloy made according to the process of claim 6.

34. An amorphous alloy made according to the process of claim 7.

35. An amorphous alloy made according to the process of claim 8.

36. An amorphous alloy made according to the process of claim 9.

37. An amorphous alloy made according to the process of claim 10.

38. An amorphous alloy made according to the process of claim 11.

39. An amorphous alloy made according to the process of claim 12.

40. An amorphous alloy made according to the process of claim 13.

41. An amorphous alloy made according to the process of claim 15.

42. An amorphous alloy made according to the process of claim 16.

43. An amorphous alloy made according to the process of claim 17.

44. An amorphous alloy made according to the process of claim 18.

45. An amorphous alloy made according to the process of claim 19.

46. An amorphous alloy made according to the process of claim 20.

47. An amorphous alloy made according to the process of claim 21.

48. An amorphous alloy made according to the process of claim 22.

49. An amorphous alloy made according to the process of claim 24.

50. An amorphous alloy made according to the process of claim 25.

51. An amorphous alloy made according to the process of claim 26.

52. An amorphous alloy made according to the process of claim 27.

53. An amorphous alloy made according to the process of claim 28.

54. An amorphous alloy made according to the process of claim 29.

55. The method according to claim 23 wherein said method forms one step in a multi-step process for forming succes#sively deposited alloy layers of opposite (p and n) conductivity type, the n-type layer being formed by exposing to the plasma during the deposition of the layer a solid phase material target including an n-dopant element which is deposited with the deposited layer to produce an n-type layer and the p-type layer being formed by exposing to the plasma during deposition of the layer another solid phase material target including a p-dopant element which is deposited with the deposited layer to produce a p-type layer.

56. The method according to claim 55 wherein there is deposited between said p and n doped layers an intrinsic amorphous alloy layer without a p or n dopant element present therein.

57. The method according to any one of claims 3 to 29 wherein said method includes providing a solid phase material target having a p or n dopant element therein and depositing at least a portion of said alloy with one of a p or n dopant element therein to form a p or n conductivity type alloy.

58. The method according to any one of claims 3 to 29 further comprising reacting the fluorine in the plasma with said removed element and thereafter depositing said removed element with the fluorine on said substrate to form said alloy body.

59. A method of making a solid phase alloy substantially as hereinbefore described with reference to and as illustrated in Figures 1 to 5 of the accompanying drawings.

60. An amorphous alloy when made by the method of any one of Claims 55 to 59.

61. An electronic device including an amorphous alloy as claimed in any one of Claims 30 to 54 or 60.

62. An electronic device when made by the method of any preceding claim and substantially as hereinbefore described with reference to and as illustrated in any one of Figures 6 to 11.