SE455554B - FOTOSPENNINGSDON - Google Patents

Description

By culturing individual monocrystals in silicon or germanium and by doping these single crystals with extremely small and critical amounts of dopant, when PN transitions are required.

These crystal culture processes yield such relatively small crystals that solar cells require the composition of many single crystals to cover the desired area for only a single solar cell panel. The amount of energy required to produce a solar cell in this process, the limitation caused by the size limitations of the silicon crystal, and the necessity of cutting and assembling such a crystalline material have all resulted in an impossible economic obstacle to the large-scale use of crystalline semiconductor crystals. cells for energy conversion. Crystalline silicon also has an indirect optical edge, which results in poor light absorption in the material. Due to the poor light absorption, crystalline solar cells must be at least 50 μm thick to absorb the incident sunlight. Even if the single crystal material is replaced by polycrystalline silicon with cheaper manufacturing processes, the indirect optical edge still remains, so the material thickness is not reduced. The polycrystalline material also includes the addition of grain boundaries and other problematic defects.

A further disadvantage of the crystalline material for solar applications is that the band gap of crystalline silicon of approximately 1.1 eV itself is below the optimal band gap of approximately 1.5 eV. Although a mixture of germanium is possible, this narrows the band gap, which further reduces the sunlight conversion efficiency. In summary, crystalline silicon devices have fixed parameters which are not variable in the desired manner, require large amounts of material, can only be produced with relatively small areas and are expensive and time-consuming to produce. Amorphous silicon-based devices can eliminate these disadvantages of crystalline silicon. Amorphous silicon has an optical absorption edge with properties similar to those of a semiconductor with a direct gap, and only a material thickness of 1 μm or less is necessary for absorbing the same amount of sunlight as crystalline silicon with a thickness of 50 μm. Furthermore, amorphous silicon can be produced faster, easier and with larger areas than crystalline silicon can.

Consequently, considerable efforts have been made to develop processes for easily depositing amorphous semiconductor alloys or films, each of which may, if desired, comprise relatively large areas, limited only by the size of the deposition equipment, and which could be easily doped to form material of P-type and N-type, when production is to take place of PN junctions, which are equivalent to those produced by their crystalline counterparts. For many years this work was largely without result. Amorphous silicon or germanium films (Group IV) are normally quadrupled and were found to have microscopic cavities and "dangling" bonds as well as other defects, which give high density of local states 1 their energy gap.The occurrence of high density of local states in the energy gap for Amorphous silicon semiconductor films result in low-grade photoconductivity and short charge life for charge carriers, making these films unsuitable for photovoltaic applications, and these films can not be successfully doped or otherwise modified to displace Fermi levels close to or valence bands, making them unsuitable for the fabrication of PN junctions for solar cell and current control applications.

In an attempt to minimize the above-mentioned problems associated with amorphous silicon and germanium, W.E. Spear and P.G. Le Comber at Carnegie Laboratory 455 554, 4 of Physics, University of Dundee, Dundee, Scotland, some work on "Substitutional Doping of Amorphous Silicon", as reported in an article published in Solid State Communications, Vol. 17, pp. Ll93- -ll96, 1975, in order to reduce the local conditions in the energy gap in amorphous silicon or germanium in order to make them more closely mimic self-conducting, crystalline silicon or germanium and to substitute the amorphous materials with suitable, classical dopants, as in the doping of crystalline materials, to make them conductive and P- or N-type conductive.

The reduction of the local conditions was accomplished by glow discharge deposition of amorphous silicon films, passing a silane gas (SiH 4) through a reaction tube, where the gas was decomposed by a radio frequency glow discharge and deposited on a substrate at a substrate temperature of about 500 ° C (227-327 ° C). C).

The material deposited on the substrate was a self-conducting amorphous material, consisting of silicon and hydrogen.

To produce a doped amorphous material, a phosphorus gas (PH3) for N-type conductivity or a diborane gas (BZHG) for P-type conductivity were mixed in advance with the silane gas and passed through the glow discharge reaction tube under the same operating conditions.

The gas concentration of the dopants used was between about 5x10 6 and 10-2 parts by volume. The material thus deposited probably contained substituting phosphorus or table tops and was shown to be an interfering conductor and an N- or P-type conductor.

Although these researchers did not know it, it is now known through the work of others that the hydrogen in the silane at an optimal temperature combines with many of the "dangling" bonds in the silicon during the glow discharge deposition to significantly reduce the density of local conditions in the energy gap. in order to bring the electronic properties of the amorphous material closer to the properties of the corresponding crystalline material.

D.I. Jones, W.E. Spear, P.G. Le Comber, S. Li and R. Martins also worked on the production of a-Ge: H from GeH4 using similar deposition techniques. The material obtained testified to a high density of local conditions in the material's energy gap. Although the material could be doped, the efficiency was significantly reduced relative to that which could be achieved with a-Si: H. In this work, reported in Philsophical Magazine B, V01. 39, p. 147 (1979), the authors conclude that due to the high density of gap condition the material obtained is ".... a less attractive material than a-Si for doping experiments and possible applications". .

In working with a similar method for glow discharge fabricated amorphous silicon solar cells utilizing the silane, D.E. Carlson to use germanium in the cells to narrow the optical gap to the optimal solar cell value of approximately 1.5 eV in his best, manufactured solar cell material, which has a “band gap of 1.65 - 1.70 ev. (DE Carlson, Journal of Non Crystalline Solids, Vol. 35 and 36 (1980), pp. 707-717, presented at the 8th International Conference on Amorphous and Liquid Semi-Conductors, Cambridge, Mass., 27-31 August 1979 ). However, Carlson has further announced that the addition of germanium from germangas was not successful, as it causes significant reductions in all the photovoltaic parameters of the solar cells. Carlson stated that the deterioration of the photovoltaic properties suggests that defects in the energy gap are created in the deposited films. (D.E. Carlson, Tech. Dig. 1977 IEDM, Washington, D.C., p 214).

In a recent report on increasing the cell efficiency of several transitions exhibiting (stacked) solar cells of amorphous silicon (a-Si: H), deposited from the silane in the above-mentioned manner, the authors reported that "gglermanium has been found to be a harmful pollution in a-Si: H, which lowers its Jsc exponentially with increasing Ge .... "From their work like Carlsons they drew that conclusion, germanium and" have been shown to have poor photovoltaic properties "and that thus new" photovoltaic film cell materials must be found which have spectral colors of 1 μm for efficient stacked cell combinations with a-Si: H (J.J. Hanak, Pellicane, presented at the 14th IEEE Photovoltaic Specia- that alloys of amorphous silicon, hydrogen response at approx. B. Faughnan, V. Korsun and J.P, lists Conference ", San Diego, California, 7-10 January 1980).

A gradation of the band gap of crystalline photovoltaic PN transition silicon solar cells was proposed in 1960 by Wolf: "Limitations and Possibilities for Improvements of Photovoltaic Solar Energy Converters", Proc IRE, vol 48, pp. 1246-1263, 1960. At the time of his report Wolf concluded that the production of crystalline semiconductor materials was technically possible, but their use in photovoltaic cells did not appear to be very useful due to the loss of Voc: In the above-mentioned article by DE Carlson, nal of Noncrystalline Solids ", vol 35 and 36 (1980), pages 707-717, Carlson also suggested that grading the band gap in the silane-deposited devices" can improve graded energy gaps "Jourdonen properties". No proposal was made on how the band gap would be graded over a significant area other than what Carlson also No proposal other than the proposal for the addition of Ge, has reported as a shortcoming. was submitted on widening the band gap. that the bandgap of amorphous Carlson later suggested silicon solar cells could be graded in a silane environment to provide a potential gradient, which would assist in the collection of photogenerated charge carriers. 455 554 7 However, it was not known how such a grading could be achieved without the addition of germanium to a ~ Si: H, which, as previously pointed out, Carlson realized caused a significant reduction in all the photovoltaic parameters of the solar cells. The inclusion of hydrogen in the above silane process not only has limitations due to the fixed ratio of hydrogen to silicon in the silane but, most importantly, different Si: H bond configurations to new anti-binding states, which can have detrimental consequences therein. material. There are therefore fundamental limitations in the reduction of the density of local conditions in these materials, which limitations are particularly disadvantageous in terms of effective P- as well as N-doping. The resulting state density in silane-deposited materials leads to a narrow depletion width, which in turn limits the efficiencies of solar cells and other devices, the work of which depends on the operation of free charge carriers.

The method of producing these materials by using only silicon and hydrogen also results in a high density of surface conditions, which affect all the above-mentioned parameters. Although the previous attempts to reduce the band gap of the material were successful in terms of gap reduction, they have at the same time further added condition to the gap. The increase in condition in the bandgap results in a decrease or total loss of photoconductivity and is thus counterproductive in the production of photosensitive devices.

After the glow discharge deposition of silane gas silicon gas was developed, work was performed on sputtering deposition 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 this molecular hydrogen on the amorphous properties of the amorphous hydrogen. silicon films. This research suggested that hydrogen acted as a compensatory agent, which was bound in such a way that it reduced the local conditions in the energy gap. However, the degree to which the local conditions in the energy gap were reduced in the sputtering deposition process was much smaller than that achieved by the silane deposition process described above. The P- and N-dopant gases described by Defovan were also introduced in the sputtering process for the production of P- and N-doped materials. These materials had a lower doping efficiency than the materials generated in the glow charging process. Neither process produced efficient P-doped materials with sufficiently high acceptor concentrations for the production of commercial PN or PIN junction devices. The N-doping efficiency was below desired acceptable commercial levels and the P-doping was particularly undesirable, as it reduced the bandgap width and increased the number of local conditions in the bandgap.

The earlier deposition of amorphous silicon, which has been modified with hydrogen from the silane gas in an attempt to make it more closely mimic crystalline silicon and which has been doped in a manner similar to that for crystallization of crystalline silicon, has properties which in all significant respects are worse than those of doped crystalline silicon. Insufficient doping efficiencies and conductivity were thus achieved especially in the P-type material, and the photovoltaic properties of these silicon films left much to be desired.

Significantly improved amorphous silicon alloys with significantly reduced concentrations of local states in their energy gaps and high quality electronic properties have been produced by glow charging, as fully described in U.S. Pat. No. 4,226,898, and by vapor phase deposition, as fully described in U.S. Pat. 217,374. As described in these patents, fluorine is introduced into the amorphous silicon semiconductor to substantially reduce the density of local states therein. Activated fluorine diffuses particularly readily into 455 554 9 and binds to the amorphous silicon in the amorphous body to significantly reduce the density of local defective states therein, since the small size of the fluorine atoms allows them to be easily introduced into the amorphous body. Fluorine binds to the dangling bonds of the silicon and forms what is believed to be a partially ionic, stable bond with flexible bonding angles, resulting in a more stable and more effective compensation or change than that formed by hydrogen and other compensating or altering agents. Fluorine is considered to be a more effective, compensating or altering substance than hydrogen, when used alone or in combination with hydrogen, due to its extremely small size, high reactivity, chemical bond specificity and highest electronegativity. Fluorine is thus qualitatively different from other halogens, and is thus considered a superhalogen.

As an example, compensation can be achieved with fluorine alone or in combination with hydrogen, the substance or substances being added in very small amounts (eg fractions of 1 atom%). However, the amounts of fluorine and hydrogen that are most desirable to use are much greater than these small percentages, so that a silicon-hydrogen-fluorine alloy is formed. These alloying substances of fluorine and hydrogen may, for example, be in the range 1-5 or more.

It is probable that the new alloy formed in this way has a lower density of defective states in the energy gap than is achieved by simply neutralizing dangling bonds and similar defective states. These larger amounts of fluorine in particular are believed to contribute significantly to a new structural configuration of an amorphous, silicon-containing material and facilitate the addition of other alloying materials, such as germanium. In addition to its other properties mentioned here, fluorine is believed to organize the local structure of the silicon containing the alloy through inductive and ionic effects. It is probable that fluorine also affects hydrogen bonding by acting in a beneficial way to reduce the density of defective states, which hydrogen contributes to while acting as a state density reducing substance. The ionic role that fluorine plays in such an alloy is believed to be a significant factor expressed in relation to the nearest neighbor.

An improved spectral response of amorphous photosensitive silicons and improved collection of photogenerated charge carriers therein is achieved in accordance with the present invention by adding one or more bandgap adjusting substances in continuously varying amounts to an amorphous, photosensitive alloy at least in one parts of its photocurrent generating area for grading the bandwidth gap for special applications without significantly increasing the harmful conditions in the gap. The material's high - quality electronic properties are thus not affected by the formation of the alloy with a graded bandgap.

The amorphous alloy includes at least one state density reducing agent, fluorine. The compensating or changing substance, fluorine, and / or other substances may be added during the sale or thereafter.

The adjusting substance or substances can be activated and can be added during vapor deposition, sputtering or glow discharge processes. The band gap can be graded as needed for a particular application by introducing varying amounts of one or more adjusting substances into the deposited alloy, at least in one or more parts of its photocurrent generation area.

The band gap is graded without a significant increase in the number of states in the band gap of the alloy and the devices due to the presence of fluorine in the alloy. The previously silane-deposited films are typically deposited on substrates heated to 250-350 ° C to maximize inside the films. The previous attempts to reduce the band gap by the understanding and compensation of silicon with hydrogen to add germanium to this film failed on the basis because the hydrogen-germanium compound is too weak to be stable in the required temperature for deposition on the substrate.

The presence of fluorine in the alloy of the invention produces a silicon alloy which differs physically, chemically and electrochemically from other silicon alloys because fluorine not only covalently binds to the silicon but also positively achieves the structural alignment of the material. This allows adjusters, such as germanium, tin, carbon or nitrogen, to be effectively added to the alloy, as fluorine forms stronger and more stable bonds than hydrogen does.

Fluorine compensates or changes silicon as well as the band-adjusting substance or substances in the alloy more efficiently than hydrogen thanks to the stronger, more thermally stable bonds and the more flexible bond configurations due to the ionic nature of the fluorine bond. The use of fluorine provides the alloy or film described in U.S. Patent No. 4,217,374, in which the state density of the band gap is much lower than that provided by a combination of silicon and hydrogen, such as from silane. Since the band-adjusting substance or substances are tailored to the material for grading the bandgap without the addition of significant harmful conditions due to the action of fluorine, the new alloy retains high-quality electronic properties and photoconductivity, and also provides an electric field throughout the semiconductor for improving photovoltaic solar energy conversion by increasing the charge carrier collection efficiency. Hydrogen further improves the fluorine-compensated or altered alloy and can be added during deposition together with fluorine or after deposition, as is the case with fluorine and other altering substances. The inclusion of hydrogen after deposition is advantageous, as it is desired to use the higher substrate temperatures for deposition allowed by fluorine. Although the principles of the present invention apply to each of the above-mentioned deposition processes, a vapor and a plasma-activated vapor deposition environment are described herein for the purpose of illustration. The glow discharge systems disclosed in U.S. Patent No. 4,226,898 which can be advantageously used in conjunction with the stem of the present invention have other process variables, principles.

Accordingly, a first object of the invention is to provide a photovoltaic device comprising superimposed layers of various materials, including an amorphous semiconductor alloy body having an active photosensitive region, comprising a bandgap, which region can be struck by radiation to provide a charge carrier, wherein the amorphous alloy comprises at least one state-reducing substance, which is fluorine.

A photovoltaic device of the type indicated in the introduction is characterized according to the invention in that the alloy further comprises in at least one cell germanium as a bandgap adjusting substance in varying amounts at least in the photosensitive range to improve its radiation absorption without significantly increasing the state of the gap. bandgap is graded for a specified photosensitivity wavelength range.

In a preferred embodiment, the bandgap of the photosensitive area may be less than 1.6 eV.

Furthermore, hydrogen can be used as a second state density-reducing substance. The alloy is suitably deposited by glow discharge deposition.

The alloy body advantageously comprises the adjusting substance in substantially discrete layers and / or in varying amounts. The alloy body according to the invention may finally form part of a Schottky barrier solar cell, a MIS solar cell, a PN adapter, a PIN device, a photodetector or a device for producing an electrical image.

The preferred embodiment of the invention will now be described, by way of example, with reference to the accompanying drawings. Fig. 1 illustrates a type of pin solar cell with a bandgap, which is graded in accordance with the present invention. Fig. 2 is a schematic view of more or less conventional vacuum deposition equipment, to which substances have been added for carrying out the addition of fluorine (and hydrogen) by the addition of molecular fluorine or fluorine containing fluorine compounds, such as SiF4, and hydrogen inlets as well as generating units for activated fluorine and hydrogen, which units decompose the molecular fluorine and hydrogen in the evacuated space of the vapor deposition equipment to convert the molecular fluorine and hydrogen to activated fluorine and hydrogen and conducting one or both to the substrate during the deposition of an amorphous alloy containing silicon. Fig. 3 illustrates vacuum deposition equipment similar to that shown in Fig. 2, together with activating means for activated fluorine (and hydrogen), which means comprise a source of ultraviolet light, which irradiates the substrate during the process of depositing the amorphous alloy, this light source replacing the generator units for the activated fluorine and hydrogen shown in Fig. 2 as well as the means for generating the adjusting substance. Fig. 4 illustrates the vacuum deposition equipment of Fig. 2, to which additional means have been added for doping the deposition alloy with a material which provides N- or P-conductivity. Fig. 5 illustrates an application where the deposition of amorphous alloy and the addition of the activated fluorine and hydrogen can be carried out as separate steps and in separate casings. Fig. 6 illustrates an exemplary apparatus for diffusing activated hydrogen into a previously deposited amorphous alloy.

Fig. 7 is a fragmentary cross-sectional view of an embodiment of a Schottky barrier solar cell illustrating an application of the amorphous photosensitive semiconductor alloys produced by the process of the invention. Fig. 8 is a fragmentary cross-sectional view of a PN junction solar device comprising a doped amorphous semiconductor alloy made by the method of the invention. Fig. 9 is a fragmentary cross-sectional view of a photodetector comprising an amorphous semiconductor alloy made by the method of the invention. Fig. 10 is a fragmentary cross-sectional view of a xerography drum comprising an amorphous semiconductor alloy prepared by the method of the invention. Fig. 11 is a fragmentary cross-sectional view of a PIN transition solar cell. Fig. 12 is a fragmentary cross-sectional view of a NIP transition solar device. Fig. 13 is a schematic view of a plasma-activated vapor deposition system for depositing the amorphous alloys together with the adjusting substance or substances according to the invention, which are incorporated in the alloys. Fig. 14 is a solar spectrum radiation diagram illustrating the normal sunlight wavelengths available for various photosensitive applications.

In Fig. 1, to which reference is first made, a pin solar cell is shown with a bandgap which is graduated in a manner according to the present invention. The band gap for the self-conducting region from the N + region to the P + region is graded from 1.2 ev to 1.8 eV, for example by adding one or more band-adjusting substances. The self-conducting (I) region can be formed by amorphous Si: F, deposited in a manner described below. The smallest band gap of 1.2 eV can be achieved by adding germanium or tin to the self-conducting range, as this is deposited. The gap can be increased from that value by decreasing the amount of germanium added during the deposition of the self-conducting layer. The final band gap value of 1.8 eV can be achieved by discontinuing the addition of the band-adjusting substance (s) germanium or tin near the end of the deposition of the self-conducting layer before the deposition of the P + layer. By adding one or more adjusting substances, which increase the band gap such as nitrogen or carbon, the band gap can be further increased to 1.8 eV or more near the P + range. The nitrogen can be added in the form of ammonia (NH3) and the carbon can be added in the form of methane (CH4). As will be described in detail later, the band-adjusting substance or substances can be added to create the graded band gap while maintaining high quality electronic properties and photoconductivity in the cell due to the inclusion of fluorine (and hydrogen) in the alloy.

As a result of the graduated band gap, improved utilization of solar energy is achieved for the generation of electron holes. Furthermore, because the band-adjusting substance or substances can be added in any amounts, a variety of different forms of grading (ie, continuous, intermittent or stepwise grading) can be achieved. In addition, the N + and P + layers can also be graded in the same way or by selective doping. The band gap can be made narrower than 1.2 eV by introducing tin into the alloy.

The graduated band gap not only provides improved solar energy utilization but also creates an electric field substantially throughout the device, which field assists in charge carrier collection. As will be seen, volume recombination in a-Si: F dominates in the absence of electric fields. This reduces the collection efficiency, as photogenerated charge carriers are lost outside the depletion area. However, due to the graduated band gap, a built-in electric field is created, which reduces the transition time compared to the life of the charge carriers, so that substantially all charge carriers are collected, provided that the field exceeds a minimum value throughout the semiconductor region.

It can also be seen from Fig. 1 that the valence band has been tilted. As illustrated, it is inclined from the N + layer to the P + layer. This slight slope allows photon-generating holes to drift toward the P + layer for collection. This slope can be achieved by selective doping in small amounts, when the self-conducting layer is deposited. Such an effect can also be achieved by building a space charge instead of by doping. Once such a space charge region is present, the holes generated will be free to move toward the P + layer for collection.

By grading the band gap in the manner illustrated in Fig. 1, a certain slight decrease in Voc will occur over an alloy with a simple band gap of 1.8 eV, since the lowest band gap in the graded alloy essentially determines Voc. However, Jsc is increased due to the more efficient use of solar energy for the generation of electron aids and the more efficient collection of the generated charge carriers. The overall operation of the device can thus be improved, especially for a use where higher currents but lower voltages are required or acceptable.

A widening of the band gap over 1.8 eV also increases the amount of sunlight available for use in the device.

Fig. 2, to which reference is now made, shows an apparatus 10 for deposition from the vapor phase, which equipment may be conventional vapor deposition equipment, to which are added means described below for injecting activated compensating or changing material.

As illustrated, this equipment comprises a glass bell 12 or similar housing enclosing an evacuated space 14 in which is located one or more crucibles, such as a crucible 16, which contains the amorphous, film-producing semiconductor blank or blanks. to be deposited on a substrate 18. In the described embodiment of the invention, the crucible 16 initially contains silicon to form an amorphous alloy containing silicon on the substrate 18, which may be, for example, a metal, a crystalline or polycrystalline semiconductor. re or other material on which it is desired to form the alloy to be deposited by the process of the present invention. An electron beam source 20 is disposed adjacent to the crucible 16, which schematically illustrated electron beam source typically includes a filament and beam deflection means (not shown) which direct an electron beam toward the silicon in the crucible 16 to vaporize it.

A high voltage DC source 22 supplies a suitably high voltage, for example 10,000 V DC, the positive connection of the source being connected via a control unit 24 and a conductor 26 to the crucible 16. The negative connection of the power source is connected via the control unit 24 and a conductor 28 to the electron beam source. 20 filaments.

The control unit 24 comprises relays or the like for interrupting the connection between the current source 22 and the conductors 26 and 28, when the film thickness of an alloy deposition sensing unit 30 in the evacuated space 14 reaches a given value, which is set by actuation of a manual control means 32 on a control panel 34 of the control unit 24. The alloy sensing unit comprises a cable 36 extending to the control unit 24, which comprises well known means for responding to both the thickness of the alloy deposited on the alloy sensing unit 30 and the rate of alloy deposition. A manual control means 38 on the control panel 34 may be provided to determine the desired rate of deposition of the alloy controlled by the value of the current supplied to the filaments of the electron beam source via a conductor 40 in a well known manner.

The substrate 18 'is supported on a substrate holder 42, on which a heater 44 is mounted. A cable 46 supplies drive current to the heater 44, which controls the temperature of the substrate holder 42 and the substrate 18 in accordance with a temperature setting determined by a manual control means 48 on the control panel 34 of the control unit 24.

The bell 12 is shown as extending upwardly from a support base 50, from which the various cables and other connections to the components within the bell 12 may extend. The support base 50 is mounted on a housing 52 which is connected to a conduit 54 which is connected to a vacuum pump 56. The vacuum pump 56, which can operate continuously, evacuates the space 14 inside the clock 12. The desired pressure in the clock is set by means of a control knob 58 on the control panel 34.

In this form of the invention, this setting controls the pressure level, at which the flow of activated fluorine (and hydrogen) is regulated into the clock 12. If the control knob is set to a clock pressure of 10-4 torr, then the flow of fluorine (and hydrogen) will into the clock 12 to be such that this pressure is maintained in the clock as the vacuum pump 56 continues to operate.

Sources 60 and 62 for molecular fluorine and hydrogen are shown connected via lines 64 and 66, respectively, to the control unit 24. A pressure sensor 68 at clock 12 is connected by means of a cable 70 to the control unit 24. Flow valves 72 and 74 are controlled by the control unit 24 for maintaining the set pressure in the watch. Lines 76 and 78 extend from the control unit 24 and pass through the support base 50 into the evacuated space 14 of the bell 12. Lines 76 and 78 are connected to the units 80 and 82 for generating activated fluorine and hydrogen, which units convert the molecular fluorine respectively. hydrogen to activated fluorine and hydrogen, which may be atomic and / or ionized forms of these gases.

The activated fluorine and hydrogen generating units 80 and 82 may be heated tungsten wires which raise the molecular gases to their decomposition temperature, or a plasma generating unit which is well known in the art for producing a plasma of decomposed gases. Activated fluorine and hydrogen in ionized forms, formed by plasma, can also be accelerated and injected into the depositing alloy by applying an electric field between the substrate and the activating source. In either case, the activated fluorine and hydrogen generating units 80 and 82 are preferably located in the immediate vicinity of the substrate 18, so that the relatively short-lived activated fluorine and hydrogen emitted from the units are immediately injected in the vicinity of the substrate 18. , where the alloy is deposited. As previously stated, at least fluorine will be included in the alloy and hydrogen will also preferably be included. The activated fluorine (and hydrogen) as well as other compensating or altering substances can also be produced from compounds containing the substances, instead of from a source of molecular gas.

For the production of useful amorphous alloys which have the desired properties for use in photosensitive devices, such as photoreceptors, solar cells, PN junction current regulators, etc., provide, as previously indicated, the compensating or altering agents, materials or substances. a very low density of local states in the energy gap without changing the basic self-conducting property of the film. This result is achieved with relatively small amounts of activated fluorine and hydrogen, so that the pressure in the evacuated bell space 14 can still be a relatively low pressure (such as -4 torr). The gas pressure in the generator can be higher than the pressure in the clock by adjusting the size of the generator outlet. The temperature of the substrate 18 is adjusted to obtain the maximum reduction in the density of local conditions in the energy gap for the amorphous alloy in question. The surface temperature of the substrate will generally be such as to ensure high mobility of the depositing materials, and preferably a temperature below the crystallization temperature of the depositing alloy.

The surface of the substrate can be irradiated with radiant energy to further increase the mobility of the depositing alloy material, for example by mounting a source of ultraviolet light (not shown) in the bell space 14. Instead of the generator units 8Q and 82 for activated fluorine and hydrogen in Fig. 2, these units may alternatively be replaced by a source 84 of ultraviolet light, shown in Fig. 3, which source directs ultraviolet energy towards the substrate 18. This ultraviolet light will decompose the molecular fluorine (and 455 554 hydrogen). both separately from and at the substrate 18 to form activated fluorine (and hydrogen), which diffuses into the depositing amorphous alloy, which is condensed on the substrate 18. The ultraviolet light improves: also the surface mobility of the depositing the alloying material.

In Figs. 2 and 3, the bandgap adjusting blanks can be added in gaseous form in an identical manner to the fluorine and hydrogen by replacing the hydrogen generator 82 or by adding one or more generators 86 and 88 (Fig. 3) for activated adjusting blank. As previously mentioned, the amount of the adjusting blank (s) is varied during the deposition to provide the graduated band gap.

Each of these generators 86 and 88 will typically be dedicated to one of the adjusting elements, such as germanium or tin. Generator 36 could, for example, supply germanium such as in the form of german gas (GeH4), or carbon in the form of methane gas (CH4).

Reference is now made to Fig. 4, which illustrates additions to the equipment shown in Fig. 2 for supplying other agents or substances to the depositing alloy. For example, an N-type conductive dopant, such as phosphorus or arsenic, may be added from the beginning to make the moderately self-conducting N-type alloy a more substantial N-type alloy, and then a P-dopant may be added. , such as aluminum, gallium or indium, are added to form a good PN junction inside the alloy. A crucible 90 is shown for receiving a dopant such as arsenic, which is vaporized by being bombarded with an electron beam from an electron beam source 92, such as the previously described radiation source 20. The rate at which the dopant evaporates to the atmosphere at 12 o'clock and which is determined by the intensity of the electron beam generated by the electron beam source 92, is set by means of a manual control means 94 on the control panel 34, which means controls the current supplied to the filament forming part in this radiation source to provide the set the rate of evaporation. The rate of evaporation is measured by means of a thickness sensing unit 96, on which the dopant material is deposited and which generates a signal on a cable 98 extending between the unit 96 and the control unit 24, which signal indicates the rate at which the dopant material is deposited on the unit 96.

After the desired thickness of amorphous alloy with the desired degree of N-conductivity has been deposited, the evaporation of silicon and of the N-type conductivity dopant is completed and the crucible 90 (or another crucible not shown) is provided with a described P-type conductivity dopant, after which the deposition process of the amorphous alloy and the dopant continue as before to increase the thickness of the amorphous alloy by an area in the P-type conductivity alloy.

The band-adjusting substance or substances can also be added by a process similar to that described for the dopant, by using another crucible, similar to crucible 90.

In the case where the amorphous alloys comprise two or more substances which are solid at room temperature, it is usually desirable to individually evaporate each substance, placed in a separate crucible, and to control the rate of deposition of each substance on something. in a suitable manner, for example by means of setting control means on the control panel 34, which in conjunction with the deposition rate and the deposition thickness sensing units control the thickness and composition of the deposition alloy. Although activated fluorine (and hydrogen) are believed to be the most advantageous compensating agents for use in compensating for amorphous alloys comprising silicon, other compensating or altering agents may be used in accordance with the further aspects of the invention. For example, carbon and oxygen may be useful in reducing the density of local states in the energy gap, as these substances are used in small amounts to change the self-conducting property of the alloy.

Although, as previously stated, it is preferred that compensating and other agents be incorporated into the amorphous alloy as it is deposited, the process of depositing amorphous alloy and the process of injecting the compensating and other agents into the semiconductor alloy may be performed in an environment. which is completely separate from the deposition of the amorphous alloy. This can give an advantage in certain applications, since the conditions for injecting such agents are then completely independent of the conditions for the alloy deposition. If the vapor deposition process produces a porous alloy, as previously explained, the porosity of the alloy can in some cases be more easily reduced by means of completely different environmental conditions than those present in the vapor deposition process. For this purpose, reference is now made to Figures 5 and 6, which illustrate the amorphous deposition process, the process for diffusion of the compensating or altering agent being carried out as separate steps in completely different environments; Fig. 6 illustrates an apparatus for performing the compensation diffusion process afterwards.

As shown, a low pressure container body 100 is provided, which has a low pressure chamber 102 with an opening 104 at its upper part. This opening 104 is closed by means of a cover 106 with threads 108, which engage around a corresponding threaded portion on the outer part of the container body 100. A sealing O-ring 110 is inserted between the cover 106 and the upper surface of the container body. A sample holding electrode 111 is mounted on an insulating bottom wall 114 in the chamber 100. A substrate 116, on which an amorphous semiconductor alloy 118 has already been deposited, is placed on the electrode 111. The upper surface of the substrate 455 554 23 116 contains the amorphous alloy 118, which is to be altered or compensated in the manner now to be described.

At a distance above the substrate 116 is an electrode 120. The electrodes 112 and 120 are connected by means of cables 122 and 124 to a direct current or radio frequency supply source 126, which applies a voltage between the electrodes 112 and 120 to provide an activated plasma of the compensating or changing the gas or gases, such as fluorine, hydrogen and the like, which are fed into the chamber 102. For simplicity, Fig. 6 illustrates only the introduction of molecular hydrogen into the chamber 102 by means of an inlet line 128 passing through the housing 106 and extends from a molecular hydrogen storage container 130. Other compensating or changing gases (such as fluorine and the like) may also be similarly fed into the chamber 102. The pipeline 128 is shown connected to a valve 132 near the container 130. A flow rate indicating gauge 134 is shown connected to the inlet line 128 beyond the valve 132. .

Suitable means are provided for heating the interior of the chamber 102 so that the temperature of the substrate is suitably raised to a temperature below but close to the crystallization temperature of the film 118. Heating wire windings 136 are shown in the bottom wall 114 of the chamber 102, to which windings a cable (not shown) is connected, which cable passes through the walls of the container body 100 to a power source for heating the bottom wall.

The high temperature together with a gas plasma, which contains one or more compensating substances and is developed between the electrodes 112 and 120, causes a reduction of the local conditions in the band gap of the alloy. The compensation or change of the amorphous alloy 118 can be enhanced by irradiating the amorphous alloy 118 with radiant energy from a source 138 of ultraviolet light, which source is shown outside the container body 100 and directs 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 may be developed by a vacuum pump (not shown), such as the pump 56 in Fig. 2. The pressure of the chamber 102 may be of the order of 3-2 dry with a substrate temperature of the order of 200-450 ° C . The activated fluorine (and hydrogen) as well as other compensating or altering substances can also be prepared from compounds containing the substances, instead of from a source of molecular gas, as previously mentioned.

A variety of uses of the improved amorphous alloys produced by the unique processes of the invention are illustrated in Figures 7-12.

Fig. 7 shows a Schottky barrier solar cell 142 in fragmentary cross section. The solar cell 142 comprises a substrate or an electrode 144 of a material having good electrical conductivity properties and the ability to make ohmic or barrier-free contact with an amorphous alloy 146, which is compensated or altered to achieve low density of local conditions in the energy gap and has a band gap. , which is optimized by the processes of the present invention. The substrate 144 may comprise a low performance metal, such as aluminum, tantalum, stainless steel or other material adapted to the amorphous alloy 146 deposited thereon, which alloy preferably comprises silicon compensated or altered in the manner of the previously described alloys. so that it has a low density of local conditions in the energy gap of preferably not more than 1016 per cm 3 per electron volt. Most preferably, the alloy has an area 148 closest to the electrode 144, which area forms a heavily doped N + type conductivity interface and with low resistance between the electrode and an undoped area 150 with relatively high dark resistance, which area is a self-conducting area with low N-type conductivity and graded band gap, as previously described.

As seen in Fig. 7, the upper surface of the amorphous alloy 146 connects to a metal area 152, the interface between this metal area and the amorphous alloy 146 forming a Schottky barrier 154. The metal area 152 is transparent or semi-transparent to solar radiation, has good electrical conductivity and has a high work function (e.g. 4.5 possibly or greater, e.g. generated from gold, platinum, palladium, etc.) relative to that of the amorphous alloy 146. The metal region 152 may be a single layer of a metal or may consist of several layers. The amorphous alloy 146 may have a thickness of about 0.5 μm and the metal region 152 may have a thickness of about 100 Å to be semi-transparent to solar radiation.

On the surface of the metal area 152, a grid electrode 156 made of a metal with good electrical conductivity is deposited. The grid may comprise orthogonally related lines of conductive material, which occupy only a small proportion of the area of the metal area, while the rest of the area shall be exposed to solar energy. The grid 156 can, for example, occupy only about 5-10% of the entire area of the metal area 152. The grid electrode 156 uniformly collects current from the metal area 152 to ensure a good, low series resistance for the device.

An anti-reflective layer 158 may be applied over the grid electrode 156 and the areas of the metal area 152 between the grid electrode areas. The anti-reflective layer 158 has a solar radiation receiving surface 160, against which solar radiation is incident. For example, the anti-reflective layer 158 may have a thickness of the same order of magnitude as the magnitude of the wavelength of the point of maximum energy in the solar radiation spectrum, divided by 4 times the refractive index of the anti-reflective layer.158. If the metal area 152 consists of platinum with a thickness of 100 Å, a suitable anti-reflective layer 158 would consist of zirconia with a thickness of approximately 500 Å and a refractive index of 2.1.

The band-adjusting blank (s) is applied to the photocurrent generating area 150 in varying amounts during deposition. The Schottky barrier 154 formed at the interface between regions 150 and 152 allows photons from solar radiation to provide charge carriers in the alloy 146, which are collected as current by the grid electrode 156. An oxide layer (not shown) may be added between layers 150 and 152 to provide - mande of a MIS (metal-insulator-semiconductor) ~ s0lcell.

In addition to the Schottky barrier solar cell or MIS solar cell shown in Fig. 7, there are solar cell structures which utilize PN junctions in the body of the amorphous alloy, which form part of the solar cell and are formed in accordance with successive deposition, compensation or modification and doping steps, such as those previously described. These other forms of solar cells are generally illustrated in Fig. 8 as well as in Figs. 11 and 12.

These structures 162 generally comprise a transparent electrode 164, through which solar radiation energy penetrates into the solar cell body in question. Between this transparent electrode and an opposite electrode 166 an amorphous alloy 168 is deposited, which alloy preferably comprises silicon and is initially compensated in the manner previously described. In this amorphous alloy 168 there are at least two adjacent areas 170 and 172, where the amorphous alloy has oppositely doped areas, the area 107 being shown as an area of N-type conductivity and the area 172 being shown as an area of P-type conductivity. The doping of areas 170 and 172 is only sufficient to move the Fermi levels to the valence and conduction bands in question, so that the dark conduction capacity increases. 455 554 27 becomes at a low value, which is achieved by the band adjustment and compensation or change method according to the invention. The alloy 168 has heavily doped, barrier-free interface areas 174 and 176 with high conductivity and the same conductivity as the alloy_l68 adjacent area. The alloy areas 174 and 176 make contact with electrodes 164 and 166, respectively. The adjusting blank or blanks are added to at least the areas 170 and / or 172 for grading the band gap.

Fig. 9, to which reference is now made, illustrates another use of an amorphous alloy utilized in a photodetector device 178, the resistance of which varies with the amount of light hitting it. An amorphous alloy 180 in the device is bandgap adjusted and compensated or altered in accordance with the invention, has no PN junctions as in the embodiment of Fig. 8 and is located between a transparent electrode 182 and a substrate electrode 184. In a photodetector device it is It is desirable that the conductivity in the dark is minimal and therefore the amorphous alloy 180 has an undoped, but compensated or altered area 186 and heavily doped areas 188 and 190 of the same type of conductivity, which later areas form a barrier-free low resistance contact with the electrodes 182 and 184, which may form a substrate for the alloy 180. The adjusting blank or blanks are added at least to the Area 186 to grade its bandgap for better sensitivity.

In Fig. 10, to which reference is made, a device 192 for producing an electrostatic image (such as a xerography drum) is illustrated. The device 192 has an undoped or weakly P-doped amorphous alloy 194 with low conductivity in the dark and selective wavelength threshold, which alloy is deposited on a suitable substrate 196, such as a drum. The adjusting substance (s) are added to the alloy 194 to grade the band gap for improved sensitivity.

As used herein, the terms compensating agent or material and modifying agent, substances or materials include those materials included in the amorphous alloy for altering or altering its structure, such as activated fluorine (and hydrogen), including the amorphous alloy. the alloy containing silicon to form an amorphous alloy with the composition silicon-fluorine-hydrogen, with a desired band gap and a low density of local conditions in the energy gap. The activated fluorine (and hydrogen) is bound to the silicon in the alloy and reduces the density of local conditions in it. Due to the small size of the fluorine and hydrogen atoms, they can both be easily introduced into the amorphous alloy without significant dislocation of the silicon atoms and their relationship in the amorphous alloy. This is especially true due to the extreme electronegativity, specificity, small size and reactivity of fluorine, all of which properties help to influence and organize the local order of the alloys. In the creation of this new alloy, the strong inductive forces of fluorine and its ability to have an organizing effect on the local system are important. Fluorine's ability to bind both silicon and hydrogen results in the formation of new and superior alloys with a minimum of local defective conditions in the energy gap. Fluorine and hydrogen are consequently introduced without significant formation of other local conditions in the energy gap in order to form the new alloys.

In Fig. 11, to which reference will now be made, a pin solar cell 198 is illustrated with a substrate 200, which may be glass or a flexible fabric, formed of stainless steel or aluminum. The substrate 200 has the desired width and length and preferably a thickness of at least 76.2 μm.

On the substrate, an insulating layer 202 is deposited by a conventional method such as chemical deposition, vapor phase deposition or anodizing in the case of aluminum substrates. The layer 202, which is, for example, um thick, may consist of a metal oxide. For an aluminum substrate it is preferably an alumina (Al 2 O 3) and for a stainless steel substrate it may be silica (SiO 2) or other suitable glass.

An electrode 204 is deposited in one or more layers on top of the layer 202 to form a base electrode for the cell 198. The electrode layer or layers 204 are deposited from the vapor phase, which is a relatively rapid deposition process. The electrode layers are preferably reflective metal electrodes of molybdenum, aluminum, chromium or stainless steel for a solar cell or photovoltaic device. The reflective electrode is preferable, since in a solar cell unabsorbed light passing 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 efficiency of the device.

The substrate 200 is then placed in the depositional environment. The particular examples shown in Figures 11 and 12 illustrate some PIN connectors which may be fabricated using improved methods and materials of the invention. Each of the devices illustrated in Figures 11 and 12 has an alloy body with a total thickness of between about 3000 and 30,000 Å.

This thickness ensures that there are no needle sticks or other physical defects in the structure and that the light absorption efficiency is maximum. A thicker material can absorb more light, but at any thickness no more current will be generated, as the greater thickness allows more recombination of the light-generated electron-halves (it will be appreciated that the thicknesses of the different layers are shown in Figs. 7-12 are not drawn to scale).

As for the formation of the NIP member 98, this is formed by first depositing a heavily doped N + alloy layer 206 on the electrode 204. Once the N + layer 206 is deposited, a self-conducting (I) alloy layer 208 is deposited on top of the layer 206. the self-conducting layer 208 is followed by a strongly doped, conductive 455 554 P + alloy layer 210, which is deposited as the last semiconductor layer. The alloy layers 206, 208 and 210 form the active layers in the NIP member 198.

Although each of the devices illustrated in FIGS. 11 and 12 may have different uses, they will now be described as photovoltaic devices. Utilized as a photovoltaic device, the selected outer P + layer 210 is a highly conductive alloy layer with low light absorption.

The self-conducting alloy layer 208 has a graded wavelength threshold for photosensitivity to sunlight, high light absorption, low dark conductivity and high photoconductivity, including sufficient and varying amounts of the adjusting substance or substances for grading the band gap. The lower alloy layer 204 is an N + layer with low light absorption and high conductivity. The total donor thickness between the inner surface of the electrode layer 206 and the upper surface of the P + layer 210 is, as previously indicated, of the size of at least about 3000 Å.

The thickness of the N + -doped layer 206 is preferably in the range of 50 - 500 Å. The thickness of the amorphous adjusting substance containing the self-conducting alloy 208 is preferably between about 3000 A and 30,000 Å.

The thickness of the upper P + edge contact layer 210 is preferably also between about 50 A and 500 A. Due to the shorter diffusion path length of the holes, the P + layer will generally be as thin as possible and of the order of 50-150 Å. For example, the outer layer (here, the P + layer 210), regardless of whether it is of the N + or P + type, will be kept as thin as possible to avoid light absorption in that contact layer and will generally not include the bandgap adjusting substance (s). A second type of PIN adapter 212 is illustrated in Fig. 12. This is a first P + layer 214 deposited on the electrode layer 204 'followed by a self-conducting amorphous alloy layer 216 containing the bandgap adjusting blank (s). in the varying amounts of 455 554 31 to grade the band gap, an amorphous N alloy layer 218 and an outer amorphous N + alloy layer 220. Although the conductive alloy layer 208 or 216 (in Figs. 11 and 12) is an amorphous alloy, furthermore, the other layers are not limited to this but may be polycrystalline, such as layer 214. (The inversion of the structure according to Figs. 11 and 12 is not illustrated but can also be used).

After 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 a separate deposition environment. It is desirable that an environment for deposition from the vapor phase be utilized, as it is a rapid deposition process. In this step, a layer 222 of transparent conductive oxide (TCO layer) is added, which may be, for example, indium tin oxide (ITO), cadmium stannate (Cd 2 SnO 4), or doped tin oxide (SnO 2). The TCO layer will be added after the subsequent fluorine (and hydrogen) compensation, if the films are not deposited with one or more of the desired compensating or altering substances in the layer. The other compensating or changing substances described above can also be added by compensating afterwards.

An electrode grid 224 may be provided by either of the means 198 or 212, if desired. For a diffuser with a sufficiently small area, the TCO layer 222 is generally sufficiently conductive, so that the grid 224 is not necessary for a good diffuser efficiency. If the diffuser has a sufficiently large area or if the conductivity of the TCO layer 222 is insufficient, For example, the grid 224 can be placed on the layer 222 to short-circuit the charge carrier path and increase the conductivity of the devices.

In Fig. 13, to which reference will now be made, an embodiment of a plasma-activated vapor deposition chamber 226 is illustrated, in which the semiconductor and the band-adjusting blank (s) of the invention can be deposited. : 455 554 32 A control unit 228 is used to control the deposition parameters, such as pressure, flow rates, etc., in a manner similar to that previously described in connection with the unit 24 (Fig. 2). The pressure would be maintained at about 10_3 One or more reaction gas pipelines, such as lines 230 and 232, can be used to supply such gases as silicon tetrafluoride (SiF4) and hydrogen (H2) to a plasma region 234. The plasma region 234 is established dry or less. between a coil 236, which is fed by a direct current source (not damaged), and an anode 238. The plasma activates the supplied gas (s) for supplying activated fluorine (and hydrogen) for deposition on a substrate 240. The substrate 240 may be heated to the desired deposition temperature by means of heating means, as previously described.

The band-adjusting substance or substances and silicon may be supplied from two or more evaporation crucibles, such as crucibles 242 and 244. Crucible 242 may, for example, contain germanium and crucible 244 silicon. The substances in the crucibles 242 and 244 can be evaporated by means of an electron beam or other heating means and activated by the plasma.

A shutter 246 can be used to vary the amounts of the band-adjusting substance or substances deposited in the photo-generating area for grading the bandgap.

The shutter speed of the shutter could be selectively controlled to vary the amount of belt adjusting substance deposited during the grading of the film. The belt-adjusting substance or substances can thus be supplied discreetly stepwise or continuously in varying amounts.

Pig 14 illustrates the available sunlight spectrum. Air mass O is the available sunlight utap '* atmosphere and with the sun at its zenith. Air mass l corresponds to the same situation after filtration through the earth's atmosphere. Crystalline silicon has an indirect band gap of approximately 1.1 - 1.2 eV, which corresponds to the wavelength of approximately 1.0 μm. This is equated with loss, ie not generation of useful photons, for essentially all light wavelengths above 1.0 μm. As used herein, the band gap or optical energy E is defined as the extrapolated intersection of a curve (añw) l / 2, where u is the absorption coefficient and hm (or e) is the photon energy. For light with a wavelength above the threshold defined by the band gap, the photon energies are not sufficient to generate a photocurrent carrier pair and thus do not supply any current to a particular device.

Another photosensitive application refers to laser wavelengths, such as for infrared response. A photosensitive material used in a high speed electrophotographic computer output device utilizing such a laser as a HeNe laser should have a wavelength scattering of about 0.6 microns. For fiber optic use, such as with GaAs lasers, the threshold of the photosensitive material should be approximately 1 μm or less. The addition of the bandgap-adjusting substance or substances according to the invention makes it possible to tailor alloys with a graded bandgap for the desired application.

Each of the transducer alloy layers of the means may be deposited by glow charging on the base electrode substrate by means of a conventional glow charging chamber, which is described in the aforementioned U.S. Pat. No. 4,226,898. The alloy layers may also be deposited in a continuous process. In these cases, the glow discharge system is initially evacuated to approximately dry to clear or eliminate pollutants in the atmosphere from the deposition system. The alloying material is then preferably fed into the deposition chamber in the form of a gaseous compound, most advantageously such as silicon tetrafluoride (SiF4), hydrogen (H2) and german (Geäéj.

The glow discharge plasma is preferably obtained from the gas mixture, the deposition system of U.S. Patent 4,226,898 is preferably operated at a pressure in the range of about 0.3 - 1.5 torr, preferably 0.6 - 1.0 torr, such as about 0.6 torr. The semiconductor material is deposited from a self-sustaining plasma on the substrate, which is heated, preferably by infrared means, to the desired deposition temperature for each alloy layer. The doped layers of the devices are deposited at different temperatures in the range from ZOOOC to about 100 ° C depending on the shape of the material used. The upper limit of the substrate temperature depends in part on the type of metal substrate used.

For aluminum, the upper temperature should not be above about 600 ° C and for stainless steel it could be above about 100oC. Prior to the production of an initially hydrogen-compensated amorphous alloy, such as to form the self-conducting layer in NIP or PIN devices, the substrate temperature should be less than about 40,000 and preferably about 300 ° C.

The doping concentrations are varied to provide the conductivity of the desired P, P +, N or N + type, as the alloy layers are deposited for each device. For N- or P-doped layers, the material is doped with 5 - 100 ppm of the doping material, as it is deposited. For N + or P + doped layers, the material is doped with from 100 ppm to over 1% of the dopant material, as it is deposited. The P-dopant material can be conventional dopants, preferably in the range from 100 ppm to over 5000 ppm for the P + material.

The glow discharge deposition process may include an AC signal generated plasma into which the material is introduced. The plasma is preferably maintained between a cathode and a substrate node with an AC signal of from about 1 kHz to 13.6 MHz.

Although the graded method and substance or substances of the invention can be used in ballasts together with a variety of amorphous alloy layers, it is preferred that they be used together with fluorine and hydrogen compensated, glow discharge deposited alloys.

In this case, a mixture of silicon tetrafluoride s: 455 554 and hydrogen is deposited as an amorphous, compensated alloy material at or below about 400 ° C for an N-type layer.

The band gap graded, self-conducting amorphous alloy layer and the P + layer can be deposited on the electrode layer at a higher substrate temperature above about 450 ° C, which will give a material which is fluorine compensated.

As an example, a mixture of the gases GeH + Ar + SiF + H 4 4 2 of GeH and SiF4 in the range 0.001 - 1% produces photosensitive alloy yarns with the graded band gaps without loss of the desired electronic properties. The mixture has a ratio of SiF4 relative to H2 of 4: 1 - 10: 1. The amount of the graded or adjusting substance (s), here germanium, in the resulting alloy is much greater than the percentages in the gas and can be considerably above 20% depending on the application. Argon is useful as a diluent but not necessary with relative percentages for the process of the invention.

Furthermore, although the bandgap adjusting blank or blanks are added at least to grade the photosensitive range of the devices, the blank or blanks may also be useful in the other alloy layers of the devices. As previously mentioned, the alloy layers other than the self-conducting alloy layer may be layers other than amorphous layers, such as polycrystalline layers (the term "amorphous" refers to an alloy or a material which is disordered at a long distance, although it may be arranged on short distance or intermediate distance or even contain some crystalline inclusions).

Claims (12)

10 15 20 25 30 455 554 36 PATENT REQUIREMENTS A photovoltaic device comprising several superimposed layers of different materials to form a stacked device on at least two series-connected solar cells, including an amorphous semiconductor alloy body having an active photosensitive region comprising bandgap which may be struck by radiation to provide charge carriers, wherein the amorphous alloy comprises at least one state density reducing substance which is fluorine, characterized in that the alloy (118, 146, 148, 150, 168, 170, 172, 174, 176, 180, 186, 188, 194, 194, 206, 208, 210, 214, 216, 218, 220) further in at least one cell comprises germanium as a band gap adjusting substance in varying amounts at least in the photosensitive range (150, 170, 172, 180, 186, 194, 208 , 216) to improve its radiation absorption without significantly increasing the conditions in the gap, the alloy band gap being graded for a specified photosensitivity wavelength range. 2. A device according to claim 1, characterized in that the bandgap of the photosensitive area is less than 1.6 ev. 3. A donor according to claim 1 or 2, wherein a second density-reducing substance, which substance is hydrogen, is known. 4. A device according to any one of claims 1-3, characterized in that the alloy (118, 146, 148, 150, 168, 170, 172, 174, 176, 180, 186, 188, 194, 206, 208 , 210, 214, 216, 218, 220) is deposited by glare charge deposition. IN" 5. A device according to any one of claims 1-4, characterized in that the alloy body (118, 146, 148, 150, 168, 170, 172, 174, 176, 180, 186, 188, 194, 206, 208 , 210, 214, 216, 218, 220) comprises the adjusting blank in substantially discrete layers. 10 15 20 455 554 37 Device according to one of Claims 1 to 5, characterized in that the alloy body comprises the adjusting substance in varying amounts. 7. A device according to any one of claims 1-6, characterized in that the alloy body forms part of a Schottky barrier solar cell (142). 8. A device according to any one of claims 1-6, characterized in that the alloy body forms part of a MIS solar cell (142). Device according to one of Claims 1 to 6, characterized in that the alloy body forms part of a PN adapter (164, 168, 166). Device according to one of Claims 1 to 6, characterized in that the alloy body forms part of a pin device (198, 212). Device according to one of Claims 1 to 6, characterized in that the alloy body forms part of a photodetector (178). Device according to one of Claims 1 to 6, characterized in that the alloy body forms part of a device (192) for producing an electrostatic image.