CA1192816A - Method for making photoresponsive amorphous germanium alloys and devices - Google Patents

Abstract

ABSTRACT
The production of improved germanium photo-responsive amorphous alloys (118, 146, 168, 180, 194, 206, 208, 210, 214, 216, 218, 220) and de-vices, such as photovoltaic (142, 168, 198, 212) photoreceptive devices (178, 192) and the like is made possible by adding at least one density of states reducing or altering element, fluorine, to the alloys (118, 146, 168, 180, 194, 206, 208, 210, 214, 216, 218, 220). The altering element or elements are added to the germanium amorphous alloys (118, 146, 168, 180, 194, 206, 208, 210, 214, 216, 218, 220) either during or after the deposition thereof. Band gap adjusting element(s) can also be added. One adjusting element is car-bon which increases the band gap from that of the materials without the adjusting element incorpo-rated therein. Other adjusting elements can be used such as nitrogen. The germanium and adjust-ing elements are concurrently combined and de-posited as amorphous alloys (118, 146, 168, 180, 194, 206, 208, 210, 214, 216, 218, 220) by vapor deposition, sputtering or glow discharge decompo-sition. The addition of fluorine bonding and electronegativity to the alloy (118, 146, 168, 180, 194, 206, 208, 210, 214, 216, 218, 220) acts as a compensating or altering element to reduce the density of states in the energy gap thereof.
The fluorine bond strength allows the adjusting element(s) to be added to the alloy (118, 146, 168, 180, 194, 206, 208, 210, 214, 216, 218, 220) to adjust the band gap without reducing the elec-tronic qualities of the alloy (118, 146, 168, 180, 194, 206, 208, 210, 214, 216, 218, 220). Hydrogen also acts as a compensating or altering element to complement fluorine when utilized therewith. The addition of the adjusting element(s) to the alloys (118, 146, 168, 180, 194, 206, 208, 210, 214, 216, 218, 220) adjusts the band gap to a selected opti-mum wavelength threshold for a particular device (142, 168, 198, 212, 178, 192) to increase the photoabsorption efficiency to enhance the device's photoresponsiveness without adding states in the gap which decrease the efficiency of the devices (142, 168, 198, 212, 178, 192). The adjusting element(s) can be added in varying amounts, in discrete layers or in substantially constant amounts in the alloys (118, 146, 168, 180, 194, 206, 208, 210, 214, 216, 218, 220) and devices (142, 168, 198, 212, 178, 192).

Description

This invention relates to a method of making amorphous germanium alloys having improved photo-responsive characteristics and devices made there-from. The invention has its most important appli-cation in making improved photoresponsive alloysand devices for speciEic applications including photoreceptive devices such as solar cells of a p-i-n, p-n, Schottky or MIS (metal-insulator semi-conductor) type; photoconducting medium such as utilized in xerosraphy; photodetecting d~vices;
and photodiodes including large area photodiode arrays; and multiple solar cell constructions.
Silicon is the basis of the huge crystalline semiconductor industry and is the material which has produced expensiv~ high efficiency (18 per cent) crystalline solar cells for space applica-tions. When crystalline semiconductor technology reached a commercial state, it became the founda-tion of the present huge semiconductor device manufacturing industry. This was due to the abll-ity 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.
~5 This was accomplished by diffusing into such crys-talline material parts per million of donor (n) oracceptor (p) dopant materials introduced as sub-stitutional impurities into the substantially pure crystalline materials, to increase their elec S tri~al conductivity and to control their being either of a p or n conduction kype. The fabri-cation processes for making p-n ~unction crystals invol~e extremely complex, time consuming, and expensive procedures. Thus, these crystalline materials useful in solar cells and current con-trol devices are produced under very carefully controlled conditions by growing individual single silicon or germanium crystals, and when p-n junc-tions are required, by e30ping such single crystals w~th extremely small and critical amounts of dop-ants.
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 crys-5 talline material have all resulted in an impos-.

sible economic barrier to the ]arge scale use of crystalline semiconductor solar cells for eneryy conversion. Further, crystalline silicon has an indirect optical edge which results in poor light S absorption in the material~ Because of the poor light absorption, crystalline solar cells have to he at least 50 microns thick to absorb the in-cident sunlight. Even if the single crystal mate-rial is replaced by polycrystalline silicon with cheaper production processes, the indirect optical edge is still maintained; hence the mat,~rial thickness is not reduced. The polycrystalline material also involves the adc~iton of grain boundariec ~.~d other problem defects.
In sulmnary, crystalline devices have fixed parameters which are not variable as desired, require large amounts of material, are only pro-ducible in relatively small areas and are ex-pensive and time consuming to produce. Devices based upon amorphous germanium or silicon can eliminate these crystal disadvantagesO ~norphous germanium and silicon have optical absorption edges having properties similar to a direct gap semiconductor and only a material thickness of one 5 micron or less is necessary to absorb the same amount of sunlight as the 50 micron thick crys-talline silicon. Further, amorphous germanium and silicon can be made faster, easier and in larger areas than can crystalline materials.
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 ~nly by the size of the deposi~
tion 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 equiva-lent to those produced by their crystalline count-erparts. For many year~ such work was substan t~ally unproductive. ~norphous germanium (Group IV) films are normally four-fo~d 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 semiconductor films results in a low degree of photoconductivity and short carrier lifetime, makin~ such films un-suitable for photoresponsive applications. Addi-5 tionally, such films cannot be successfully doped4-or otherwise modified to shift the Fermi level close to the conduction or valence bands, maki;lg them unsuitable for making p-n junctions for solar cell and current control device applications~
In an attempt to minimize the aforementioned problerns involved with amorphous alloys, W.~.
Spear and P~G. LeComber of Carnegie Laboratory of ~hysics r Universi.ty o~ D~lndee, in Dundee, Scotland, did some work on "S~lbstitutional Doping of ~nor-phous Silicon", as reported in a paper published in Solid State Col~nunicati~ns, Vol. 17r pp~ 1193-1196, 1975, toward the end of reducing the local-izec~ states in the energy gap in amorphous alloys to make the same approximate more closely in-trinsic crystalline silicon or germanium and of substitutionally doping the amorphous materials with suitable classic dopants, as in doping crys-talline 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 amor-phous alloys, in th.is case, silicon films, wherein a gas of silane ~SiH4) wa~s passed through a re-action tube where the gas was decomposed by an r.f. glow discharge and deposited on a substrate at a substrate temperature of about 500-600K
(227-327C). The material so deposited on the substrate was an intrinsic amorphous material consisting of silicon and hydrogen. To produce a doped amorphous material a ~as of phosphine (P~3) for n type conduction or a yas of diborane (B2H6) for p-type conduction were premixed with the si-lane gas and passed through the glow discharge reactio~ tube under the same ~perating conditions.
The gaseous concentration of the dopants used was between about 5 x 10-6 and 10-2 parts per volume.
The material so deposited included supposedly sub-stitutional phosphorus or boron dopant and was shown to be extrinsic ancl of n or p conduction type.
Whi,e 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 localiæed states in the energy gap toward the end of making the electronic properties of the amorphous mate-rial approximate more nearly those of the cor-responding crystalline material.

D.I. Jones, W.E. Spear, P.G. LeComber, S. Li,and R. Martins also worked on preparing a-~e:H
from GeH~ using similar deposition techniques.
The material obtained gave evidence of a high density of localized states in the energy gap thereof. ~lthough the material could be doped the eEficiency was substantially reduced from that obtainable with a-Sl~H. In this work reported in Philosophical Magazine B, Vol. 39, p. 147 (1979) the authors conclude that because of the large density of gap states, the a~Ge:H mate~ial obtain-ed is 11. . ~ a less attractive material than a-S1 for doping experiments and possible applieations."
The prior deposition of amorphous germanium, which has been doped in a manner like that of doping crystalline germanium, has characteristics which in all important respects are inferior to its doped crystalline counterpart. Thus, inade-quate doping efEiciencies and conductivity were achieved and the photovoltaic qualities of these 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 pre~

pared by glow discharge as fully described in U.S.
Patent No. 4,226,898, Amorphous Semiconductors Equivalent to Crystalline 5emiconductors, Stanford R. Ovshinsky and Arun Madan which issued October 7, 1980, and by vapor deposition as fully des-cribed 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, fluorine is introduced into the amorphous silicon semiconductor to substantially reduce the density of localized states therein.
Activated fluorine especially readily dif-fuses into and bonds to the amorphous silicon in the matrix body, substantially to decrease the density of localized defect states therein, be-cause the small size of the fluorine atoms enables them to be readily introduced into the amorphous silicon matrix. The fluorine bonds to the dangl-ing bonds of the silicon and forms what is be-lieved to be a partially ionic stable bond withflexible bonding angles, which results in a more stable and more efficient compensation or altera-tion than is formed by hydrogen and other compen-sating or altering agents. Fluorine is considered 5 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. Hence, fluorine is qualitatively different from other halogens and so is considered a super-halogen.
As an example, compensation may be achieved with fluorine alone or in combination with hydro-gen 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-hydrogen-fluorine allc,y. Such alloying amounts of fluorine and hydrogen may, for example, be in the range of 1 to 5 percent or greater. It is be-lieved that the new alloy so formed has a lower density of defect states in the energy gap than that achieved by the mere neutràlization of dangl-20 ing bonds and similar defect states. Such largeramount of fluorine, in particular, is believed ~o participate substantially in a new structural configuration of an amorphous silicon-containing material and facilitates the addition of other al-loying materials, such as germanium. Fluorine, in _g_ addition to its other characteristics mentionedherein, is believed to be an organi~er 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 denslty of defect stat~s which hydrogen contri-butes 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 fac tor in terms of the nearest neighbor relation-ships.
The problem associated with the prior art preparaton of amorphous germanium suitable for use in photoresponsive devices i5 overcome in ac-cordance with the present invention by adding one or more density of states reducing elements to the alloy during or after the deposition thereof~ The germanium alloy can incorporate at least one of the density of states reducing elements itself or the elements can be added separately during the deposition. The improved germanium alloy can be deposited by vapor deposition, sputtering or glow discharge processes.
Preferably, the amorphous alloy incorporates at least one density of states reducing element, fluorine. The compensating or altering element, fluorine, and/or other elements can be added dur~
ing deposition or thereafter. Band gap adjusting element(s) can be activated and may be added dur-ing the vapor deposition, sputtering or glow dis-charge processes. The band gap can be adjusted as required for a specific application by introducing the nec~ssary amount of one or more of the ad-justing elements into the deposited alloy in atleast the photocurrent generation region thereof.
The band gap can be adjusted without sub-stantially increasing the number of states in the band gap of the alloy a~d devices, because of the p~esence of fluorine in the alloy. Tjhe presence of fluorine in the alloy of the invention provides a germanium alloy which differs physically, chemi-cally and electrochemically from other germanium alloys because fluorine not only covalently bonds to the germanium but also affects in a positive manner the structural short range order of the material. This allows the adjusting elements, such as carbon or nitrogen, effectively to be added to the alloy, because fluorine forms stronger ~L~19~

and more stable bonds than does hydrogen. Fluo-rine compensates or alters germanium as well as the band adjusting element(s) in the alloy more efficiently than hydrogen, because oE the stronger more thermally stable bonds and more flexible bonding configurations due to the ionic nature of the fluorine bonding.
The band adjustin~ element(s) are tailored into the material w thout ad~ing substantial dele-terious states because of the influence of fluorine. The new alloy therefore maintains high quality electronic quali.ties and photoconductivity when the adjusting element(s) are added to tailor the wavelength threshold for a specific photo-response appl.ication. Hydrogen further enhancesthe 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 tempera-tures allowed by fluorine.
While the principles of this invention apply to each of the aforementioned deposition pro-5 cesses, for purposes of illustration herein a-12-vapor and a plasma activated vapor depositionenvironment are described. The glow discharge system disclosed in U.S. Patent No. 4,226,898 has other process variables which advantageously can be utilized with the principles of this invention.
We have found that the above disadvantages may be overcome if the germanuim containing amor-phou~ alloy includes at least fluorine to reduce the density of states therein, to thereby allow the inclusion of one or more band gap adjusting elements without substantially increasing the states in the gap. The alloy thus may have a band gap adjusted for a sp~cified photoresponse wave-length function for use in various devices in-cluding, for example~ p~n and p-i-n, Schottky, or MIS solar cells, photo-detectors and electrostatic image producing devices.

The preferred embodiment of this invention will now be described by way of example with ref-erence to the drawings accompanying this specifi-cation in which:
Fi~ 1 is a diagrammati~ representation of more or less conventional vacuum deposition equip-ment to which has been added elements. for carry.ing out the addition of fluorine (and hydrogen) by the addition of molecula~ or fluorine compounds con-taining fluorine such as GeF4~ and hydrogen inlets and activated fluorine and hydrogen gen~rating units which decompose the molecular fluorine and hydrogen within the evacuated space of the vapor deposition equipment, to convert molecular flu-orine and hydrogen to activated fluorine and hy-drogen and to direct one or both against the sub-strate during the deposition of an amorphous alloy containing germanium;
Fig. 2 illustrates vacuum deposition equip-ment like that shown in Fig. 1, with activated fluorine ~and hydrogen) generating means com-prising an ultraviolet light source irradiating the substrate during the process of depositing the germaniu~ aInorphous alloy, such light source re-placing the activated fluorine and hydrogen gener-ator units shown in Fig. l and adjusting element generating means;
Fig. 3 illustrates the vacuum deposition e~uipment for Fig. l to which has been added ad-ditional means for doping the depositing alloy with an n or p conductivity producing material;
Fig. 4 illustrates an application wherein the deposition of the germanium 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 fluorine into a previously deposited germanium amorphous alloy;
Fig. 6 is a fragmentary sectional view of an embodiment of a Schottky barrier solar cell to illustrate one application of the germanium amor-phous semiconductor photoreceptive alloys made bythe process of the invention;
Fig. 7 is a fragmentary sectional view of a p-n junction solar cell Aevice which includes a doped germanium amorphous semiconductor alloy made 5 by the process of the invention;

~2~

Fig. 8 is a fragmentary sectional view of a photo-detection device which includes an amorphous germanium semiconductor alloy made by the process of the invention;
Fig. 9 is a fragmentary sectional view of a xerographic drum including an amorphous germanium semiconductor alloy ~lade 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;
Fig. 12 is a diagrammatic representation of a plasma activated vapor deposition system for depo-siting the germanium amorphous alloys with theadjusting element(s) of the invention incorporated therein; and Fig. 13 is a solar spectral irradiance chart illustrating the standard sunlight wavelengths available for various photoresponsive applica-tions.
Referr1ng now more particularly to Fig. 1, there is shown vapor deposition equipment general-ly indicated by reference nuJneral 10, which may be 5 conventional vapor deposition equipment to which is added an activated compensating or alteringmaterial injecting means to be described. This equipment, as illustrated, incluc~es a bell jar 12 or similar enclosure enclosing an evacuated space 14 in which is located one ~r more crucibles like crucible 16 containing the amorphous semiconductor :~.ilm-producing element or elements to be deposited on a substrate 18. In the form of the invention being described, the crucible 16 initially con-tains germanium for forming an amorphous alloycontaining germanium on the substrate 18 which, for example, may be a metal, crystalline or poly-crystalline semiconductor or other material upon which it is desired to form the alloy to be de--posited by the process of the present inventionOAn electron beam source 20 is provided adjacent to the crucible 16, which electron beam source, dia-grammatically illustrated, usually includes a heated filament and beam deflection means (not shown) which directs a beam of electrons at the germanium contained in the crucible 16 to evapo-rate the same.
A high voltage DC power supply 22 provides a suitable high voltage, for example 10,000 volts 5 DC, the positive terminal of which is connected through a control unit 24 and a conductor 26 tothe crucible 16. The negative terminal of which is connected through the control unit 24 and a conductor 28 to the filament oE the electron beam source 20. The control unit 24 including relays or the like for interruptlng the connection oE the power supply 22 to the conductors 26 and 28 when the film thickness of an alloy deposition sampling unit ~0 in the evacuated space 14 reaches a given value set by operating a manual control 32 on a control panel 34 of the control unit 24. The alloy sampling unit 30 inc~udes a cable 36 which extends to the control unit 24 which includes well known means for responding to both the thickness of the alloy deposited upon the alloy sampling unit 30 and the rate of deposition thereof~ A
manual control 38 on the control panel 34 may be provided to fix the desired rate of deposition of the alloy controlled by the amount of current fed ~0 to the filament of the electron beam source through a concluctor 40 in a well known manner.
The substrate 18 is carried on a substrate holder 42 upon which a heater 44 is mounted. A
cable 4S feeds energizing current to the heater 44 5 which controls tne temperature of the substrate holder 42 and substrate 18 in accordance with a temperature set~ing set on a manual control 48 on the control panel 34 of the control unit 24.
- l'he bell jar 12 is shown extending upwarc~ly 5 from a support base 50 from which the various cables and other connections to the components within the bell jar 12 may extend. l'he support base 50 is mounted on an enclosure 52 to which connects a conduit 54 connecting to a vacuum pump 56. The vacuum pump 56, which may be continuously operated, evacuates the space 14 within the bell jar 12. The desired pressure of the bell jar is set by a control knob 58 on the control panel 34.
In this form of the invention, this setting con-trols the pressure level at which the flow ofactivated fluorine ~and hydrogen) into the bell jar 12 is regulated. Thus, iE the control knob is set to a bell jar pressure of 10-4 torr, the flow of fluorine (and hydrogen) into the bell jar 12 20 will be such as to maintain such pressure in the bell jar as the vacuum pump 56 continues to oper-ate.
Sources 60 and 62 of molecular fluorine and hydrogen are shown connected through respective conduits 64 and 66 to the control unit 240 A

pressure sensor 68 in the bell jar 12 is connected by a cable 70 -to the control unit 24. E~low valves 72 and 74 are controlled by the control unit 24 to maintain the set pressure in the bell jar. Con-s duits 76 and 78 extend from the control unit 24 and pass through the support base 50 into the evacuated space 14 of the bell jar 12, Conduits 76 and 78 respectively connect with activated fluorine and hydro~en generating units 80 and 82 which convert the molecular fluorine and hydrogen respectively to activated fluorine and hydrogen, which ~ay be atomic and/or ionized forms of these gases. The activated fluorine and hydrogen gen-erating units 80 and 82 can be heated tungsten filaments which elevate the molecular gases to their deco~nposition temperatures or a plasma gen-erating unit well known in the art for providing a plasma of decolaposed gases. Also, activated flu-orine and hydrogen in ioniæed forms formed by plasma can be accelerated and injected into the depositing alloy by applying an electric field between the substrate and the activating source.
In either event, the activated fluorine and hy-drogen generator units 80 and 82 are preferably placed in the immediate vicinity of the substrate ~9~8~;

18, so that the relatively short-lived activated fluorine and hydrogen delivered thereby are im-mediately injected into the vicinity of the sub-strate 18 where the alloy is depositing. As in-dicated previously, at least fluorine will beincluded in the alloy and hydrogen preferably also will be included. The activated fluorine (and hydrogen) as well as other compensating or alter-ing elements also can be produced from compounds containing the elements instead of from a molec-ular gas source.
As previously indicated, to produce useful amorphous alloys which have the desired charac-teristics for use in phokoresponsive devices such as photoreceptors, solar cells, p-n j~nction cur-rent control devices, e~c., the compensating or altering agents, materials or elements produce a very low density of locali~ed states in the energy gap without changing the baslc intrinsic character of the film. This result is achieved with rela tively small amounts of activated fluorine and hydrogen so that the pressure in the evacuated bell jar space 14 can still be a relatively low pressure (like 10-4 torr). The pressure of the gas in the generator can be higher than the pres-

2~

sure in the bell jar by adjusting the size of the outlet of the generator~
The temperature of the substrate 18 is ad-justed to obtain the maximum reduction in the density of the localized stat.es in the energy gap of the amorphous alloy involved. The substrate s~rface temperature will generally be such that it ensures high mobility of the depositing materials, and preferably one Del3w the crystallization tem-perature o:E the depositing alloy.
The surface of the substrate can be irradi-ated by radiant energy to rurther increase the mobility of the depositing alloy material, as by mounting an ultraviolet light source (not shown) in the bell jar space 14. Alternatively, instead of the activated fluorine and hydrogen generator units 80 and 82 in Fig. 1, these units can be replaced by an ultraviolet light source 84 shown in Fig. 2, which directs ultraviolet energy against the substrate 18~ This ultraviolet light will decompose the molecular fluorine (and hydrogen) both spaced from and at the substrate 18 to form activated fluorine (and hydrogen) which diffuses into the depositing amorphous alloy condensing on 5 the substrate 18. The ultraviolet light also enhances the surface mobility of the depositingalloy material.
In Figs. 1 and 2, the band gap adjusting elements can be added in gaseous form in an iden-tical fashion to the fluorine and hydrogen byreplacing the hydrogen generator 82 or by adding one or more activated adjustiny element generators 86 and 88 ~Fig. 2). Each of the generators 86 and 88 typically will be dedicated ~o one o~ the ad-justing elements such as carbon or nitrogen. Forexample, the generator 86 could supply carbon as in the fonn of methane gas ~CH4), and generator 88 could supply nitrogen as in the ~orm of ammonia gas (NH3).
Referring now to Fig. 3 which illustrates additions to the equipment shown in Fig. 1 for adding other agents or elements to the depositing alloy. For example, an n-conductivity dopant, like phosphorus or arsenic, may be initially added to make the intrinsically modest n-type alloy a more substantially n-type alloy, and then a p-dopant like aluminum, gallium or indium may be added to form a good p-n junction within the alloy.
A crucible 90 is shown for receiving a dopant like arsenic which is evaporated by bombarding the same with an electron beam source 92, like the beam source 20 previously described. The rate at which the dopant evaporates into the atmosphere of the bell jar 12, which i5 determi.ned by the intensity of the electron beam prod~ced by the electron beam source 92, is set by a manua]. control 94 on the colltrol panel 34, which controls the current fed to the filament forming part o~ this beam source to produce the set evaporatioll rate. ~he evapora-tion rate is measured by a thickness sampling unit96 upon which the dopant material deposits and which generates a signal on a cable 98 extending between the unit 96, and control unit 24, which indicates the rate at which the dopant material is deposited on the unit 96.
After the desired thickness of amorphous alloy having the desired degree of n-conductivity has been deposited, evaporation of germanium and the n-conductivity dopant is terminated and the crucible 90 (or another cruci.ble not shown) is provided with a p-conductivity dopant described, and the amorphous alloy and dopant deposition process then proceeds as before to increase the thickness of the amorphous alloy with a p-conduc-tivity region therein.

J~

The band adjusting element(s) a:Lso can be added by a similar process to that described for the dopant by utilizing another crucible similar to the crucible 90.
In the case where the amorphous alloys com prise two or more elements which are solid at room temp~rature, then it is usua]ly desirable to sepa-rately vaporize each el~ment placed in a separate crucible, and control the de~osition rate thereof in any suitable manner, as by setting controls on the control panel 34 which, in association with the deposition rate and thickness sampling units, controls the ~hickness and composition of the depositing alloy.
While activated fluorine (and hydrogen) are believ~d to be the most adYantageous compensating agents for use in compensating amorphous alloys including germanium, in accordance with broader aspects of the invention, other compensating or altering agents can be used. For example, carbon and oxygen may be useful in reducing the density of localized states in the energy gap when used in small amounts so as not to change the intrinsic characteristic of the alloy.
As previously indicated, although it is pre--25~

ferred ~hat compensating and other agents be in-corporated into the amorphous alloy as it is depo-sited, 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 ~emiconductor alloy can be done in a completely separate envirorlment from the depositing oE 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 vapor deposition process produces a porous alloy, the porosity o~ the alloy, in some cases, is more easily reduced by environmental conditions quite different from that present in the vapor deposition process. To this end, reference should now be made to Figs. 4 and S which illustrate that the amorphous deposition process and the com-pensating or altering agent diffusion process are carried out as separate steps in completely dif-ferent environments, Fig. 5 illustrating apparatus for carrying out the post compensation diffusion process.
~s 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-rin~ 110 is sandwiched between the cap 106 and the upper face of the container body. A sample-holding electrode 112 is mounted on an insul~ting bottom wall 114 of the chamber 100. A substrate 116 upon which an amor-phous germanium alloy 118 has already been de-posited is placed on the electrode 112. The upper face of the substrate 116 contains the amorphous alloy 118 to be alte~ed or compensated in the rnanner now to be described.
Spaced above the substrate 116 is an elec-trode 120. The electrodes 112 and 120 are con nected by cables 122 and 124 to a DC or RF supply source 126 which supplies a voltage between the 2n electrodes 112 and 120 to provide an activated plasma of the compensating or altering gas or gases~ such as fluorine, hydrogen, and the liker fed into the chamber 102. For purposes of sim-plicity, Fig. 5 illustrates only molecular fluo-5 rine being fed into the chamber 102 by an inlet conduit 128 passing through ~he cap 106 and ex-tending from a supply tank 130 of molecular fluo-rine. Other compensating or altering gases (such as hydrogen and the l.ike) also ma,y 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 con nected to the inlet conduit 128 beyond the valve Suitable means are provided for heating the interiox of the chamber 102 so that the substrate temperature is elevated pre~erably to a tempera-ture below, but neax the crystallization tempera-ture of the film 118. ~or example, coils of heat-ing 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 con-tainer body 100 to a source of current for heating the same.
~0 The high temperature together with a plasma of gas containing one or more compensating ele-ments developed between the electrodes 112 and 120 achieve a reduction of the localized states in the band gap of the alloy. The compensating or alter- 5 ing of the germanium amorphous alloy 118 may be enhanced by irradiating the amorphous alloy 118 with radiant energy from an ultraviolet light source 138, which i5 ShOWIl O~ltside of the con-tainer body 100 directing ult:raviolet light be-tween the electrodes 112 and 120 through a quartz window 140 mounted in the sic~e wall of the con-tainer body 100~
The low pressure cr 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 450C. 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 amor-phous 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 prop-erties, and the ability of making an ohmic contact with an amorphous germanium alloy 146 compensated or altered to provide a low density of localized states in the energy gap and with a band gap op-timized by the processes of the present invention.
~he substrate 144 may comprise a low work function metal, such as aluminum~ tantalum, stainless ~teel or other material matching with the amorphous ~lloy 146 deposited thereon which preferably in-cludes germanium, 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. It is most pre~erred 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 15G 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 5 electrical conductivity and is o~ a high work function (for example, 4.5 eV or greater, pro-duced, 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 amorphows alloy 146 may have a thickness of about .5 to 1 micron and the metallic region 152 may have a thickness of about 100A in order to be semi-trans-parent 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 rel~ted 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 156 may occupy only about from 5 to 10~ of the entire area of the metallic region 152. The grid electrode 156 uniformly col7ects current from the metallic region 152 to assure a good low se-ries resistance for the device.
An anti-reflectlon layer 158 may be applied over the grid electrode 156 and the areas of the metallic region 152 between the grid electrode areas. The anti-reflection layer 158 has a solar radia~ion inciden~ surface 160 upon which impinges the solar radiation. For example, the anti-re-flection layer 158 may have a thickness on the order oE magnitude of the wavelength of the maxi-mum aner~y point of the solar radiation spectrum,divided by four times the index o refraction of the anti reflection layer 158 If the metallic region 152 is platinum of lOOA in thickness, a suitable anti-reflection layer 158 would be zir-conium oxide of about SOOA in thickness with anindex of refraction of 2.10 The band adjusting element(s) are added to the photocurrent generating region 150. The Schottky barrier 154 formed at the interface between the reglons 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 karrier or MIS
solar cell shown in FigO 6, there are solar cell constructions which utilize p-n junctions in the Z5 body of the amorphous alloy forming a part thereof 2B~L~

formed in accordance with successive deposition~
compensating or altering and doping steps like that previously described. The~e other forms of solar cells are generically illustrated in Fig. 7 as well as in Figs. 10 and 11.
These constructions 162 generally include a t:ransparent electrode 164 through which the solar radiation energy penetrates into the body of the solar cell involved~ Between this tra~sparent electrode and an opposite electrode 166 is a depo-~ited amorphous alloy 168 r preferably including germanium, initially compensated in the manner previously described. In this amorphous alloy 168 are at least two adjac~nt regions 170 and 172 where the amorphous alloy has respectively oppo-sitely 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 reyions 170 and 172 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 ]68 has high conductivity, highly doped ohmic contact interface regions 174 and 176 of the same conductivi~y type as the adjacent region of the alloy 168. The alloy regions 174 and 176 contact electrodes 164 and 166, respectively. The adjusting element(s) are added to regions 170 and/or 172.
Referring now to Fig. 8, there is illustrated another application of an amorphous alloy utilized in a photo-detector device 17B whose resistance varies with the amount of 1ight impinging thereon.
lG An amorphous alloy 180 thereof i5 band gap ad-justed and compensated or altered in accordance with the invention, has no p-n junctions as in the embodiment shown in Fig. 7 and is located between a transparent electrcde 182 and a substrate elec-trode 184. In a photo-detector device it is de-sirable to have a minimum dark conductivity and so the amorphous alloy 180 has an undoped, but com-pensated 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 184, which may form a substrate for the alloy 180. The adjusting element(s) are added at least to the region 186.
Referring to Fig. 9 an electrostatic image 5 producing device 192 (like a xerography drum) is ~34-illustrated. ~he device 192 has a low dark con-ductivityl selective wavelength threshold, undoped or slightly p-doped amorphous alloy 194 deposited on a suitable substrate 196 such as a drum. The adjusting element(s) are added to the alloy 194.
As used herein, the terms compensating agents or materials and altering agents, elements or materials mean material~ which are incorporated in the germallium amorphous alloy for altering or changing ~he structure thereof, such as, activated fluorine (and hydrogen) incorporated in the amor~
phous alloy containing germanium to form an amor-phous germanium/fluorine/hy~Eogen composition allvy, having a desired band gap and a low density of localized states in the energy gap. The acti-vated fluorine (and hydrogen) is bonded to the germanium 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 with-out substantial dislocation of the germanium atoms and their relationships in the amorphous alloy.
This is true most particularly because of the ex-treme electronegativity, specificity, small size 5 and reactivity of fluorine, all of which char-ac~eristics organize the local order of the al-loys. In creating this new alloy the strong in-ductive powexs of fluorine and its ability to act as an organizer of short ranqe order is of impor-S tance. The ability of fluorlne to bond with bothgermanium and hydrogen resull:s in the formation of alloys with a minimum of localized defect states in the energy gap. Hence, fluorine and hydrogen are introduced witho~t substantial formation of other localized states in the energy gap to form the new alloy.
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 stain-less steel or aluminum. The substrate 200 i5 of awidth and length as desired and preferably at least 3 mils thick. The substrate has an in-sulating layer 202 deposited thereon by a con~Ten-tional 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 substratel it preferably is aluminum oxide ~A12O3) 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 i5 a relatively fast deposition process. The elec-trode layers preferably are r~flective metal elec-trodes of molybdenum, aluminum, chrome or stain-less ~teel for a solar cell or a photovoltaic device. The reflect~ive electrode is preferable since, in a solar cell, non-absorbed light which passes through the semiconductor alloy is re-flected from the electrode layers 204 where it again passes through the semiconductor alloy which then absorbs more of ~he light energy to increase the device efficiency.
The substrate 200 is then placed in the de-position environment. The specific examples shown in Figs. 10 and 11 are illustrative of some p i-n junction devices which can be manufactured util-izing the improved methods and materials of theinvention. Each of the devices illustrated in Figs. 10 and 11 has an alloy body having an over-all thickness of between about 3,000 and 30,000 angstroms. This thickness ensures that there are 5 no pin holes or other physical defects in the structure and that there is maximum light ab-sorption efficiency. A thiclcer material may ab-sorb more light, but at some thickness will not generate more current since the greater thickness s 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 ll are not drawn to scale.) Referring first to forming the n-~-p device 1~8, the device i5 formed by first depositing a heavily doped n~ alloy layer 206 on the electrode 204. Once the n+ layer 206 is deposited, an in-trinsic (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 alloy layers 206, 208 and 210 form the active layers o the n-i-p device 198.
While each of the devices illustrated in Figs~ 10 and ll 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 2~ alloy layer 208 has an adjusted wavelength thresh-old for a solar photoresponse, high light absorp-tion, low dark conductivity and high photocon-ductivity including su~ficient amounts of the adjusting element~s) to optimize the band gap.
The bottom alloy layer 204 is a low light absorp-tion, high conductivity n* layer. The overall device thickness between the inner surEace of the e:Lectrode layer 206 and the top surface of the p~
layer 210 is, as stated pre~iously, 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 adjustin~ element containing intrinsic alloy 208 is preferably between about

3,000 angstroms to 30,000 angstroms. The thick-ness of the top p+ contact layer 210 also is pre ferably 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 o~
light in that contact layer and generally will not include the band gap adjusting element(s).
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 germanium amorphous alloy layer 216 containing the hancl gap adjusting ele-ment(s~ in the desired amount:, an n amorphousalloy layer 218 and an outer n~ amorphous alloy layer 220. Further, although the lntrinsic alloy layer 208 or 216 (in Figs. 10 and 11) is an amor-phous alloy the other layers are not so restricted and may be polycrystalline, such as layer 214.
(The inverse of the Figs. 1~ and 11 structure not illustrated~ also can be u~ilized.) Following the deposition of the various semi-conductor alloy layers in the desired order for the devices 198 and 212, a further deposition step is performed, preferably in a separate deposition environment~ Desirably, a vapor deposition envi-ronment i5 utilized since it is a fast deposition process. In this step, a TCO layer 222 (trans-parent conductive oxide) is added which, for ex-ample, may be indium tin oxide (ITO), cadmium stannate (Cd2SnO~), or doped tin oxide (SnO2).
The TCO layer will be added following the post compensation of fluorine (and hydrogen) if the 5 films were not deposited with one or more of the desired compensating or altering elements therein.
Alsol the other compensating or altering elements, above described, can be added by post compensa-tion.
An electrode grid 224 can be added to either of the devices 198 or 212 if desired. For a cle-~ice having a sufficiently small area, the TCO
layer 222 is generally sufficiently conductive such that the grid 224 is not necessary for good device efficiencyD If the device is of a suf-ficiently 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~
Referring now to Fig. 12, one embodiment of a plasma activated vapor deposition chamber 226 is illustrated in which the semiconductor and hand adjusting element(s) of the invention can be de-posited. A control unit 228 is utilized to con-trol the deposition parameters, such as pressure, flow rates, etc., in a manner similar to that previously described with respect to the unit 24 (Fig. 1). The pressure would be maintained at about 10-3 torr or lessO
One or more reaction gas conduits, such as 230 and 232, can be utilized to supply gases such as germanium tetrafluoride (GeF4) and hydrogen (H2) into a plasma region 234. The plasma region 234 is established between a coil ~36 fed by a DC
power supply (not illustra~ed) and a plate 238.
The plasma activates the supply gas or gases to supply activated fluorine (and hydrogen) to be deposited on a substr~te 240. The substrate 240 may be heated to the desired deposition temper-ature by heater means as previously described.
The band adjusting element(s) and germaniumcan be added from two or more evaporation boats, such as 242 and 244. The boat 242 could, for ex-ample, contain germanlum and the boat 244 would contain carbon. The elements in boats 242 and 244 can be evaporated by electron beam or other heat-ing means and are activated by the plasma.
If it is desired to layer the band adjusting element(s) in the photogenerating region of the film being deposited, a shutter 246 can be uti-lized. The shutter could rotate layering separate band adjusting elements from two or more of the boats or can be utilized to control the depositing of the band adjusting element from the boat 244 5 (or others) to provide layers in the film or to vary the amount of band adjusting element depos ited in the film. Thus, the band adjusting ele-ment(s) can be added discretely in layers, in substantially constant or in varying amounts.
Fig. 13 illustrates the available sunlight spectrum. Air ~ass O (AMO) being the sunlight available with no atmosphere and the sun directly overhead. AMl corresponds to the same situation after filtering by the earth's atmosphere. Crys-talline germanium has an indirect band gap of about .7 eV, which corres~onds to the wavelength of about 1.8 micrometer (microns). This equates to losing, i.e. not generating useful photons, for substantially all the light wavelengths above 1.8 microns. As utilized hereinl band gap or E opti-cal is defined as the extrapolated intercept of a plot of (oc~u~l/2, whereo~ is the absorption co-efficient an ~ u~ (or e) is the photon energy.
For light having a wavelength above the threshold deined by the band gap, the photon energies are not sufficient to generate a photocarrier pair and hence do not add any current to a specific device.
Calculations for the maximum theoretical conversion efficiency as a function of the width 5 of the band gap were done by J.J. Loferski, as reported in Journal of Applied Physics, Vol. 27,p. 777~ July, 1956. For single band gap mate-rials, depending upon the assumptions made, the optimum band gap is on the order of 1.4 to 1.5 eV
for solar applicationsi To produce the desired photovoltaic band gap of 1.5 eV in the amorphous devices, the band adjusting lelement(s) of the in~
vention, such as carbon or nitrogen are added to the photogenerating regions, as previously des-cribed.
Another photoresponsive application is forlaser wavelengths such as for infrared response.
A photoresponsive material used in a high speed electrophotographic c~mputer output device uti-lizing a laser, such as a helium neon laser, shouldhave a wavelength threshold greater than .6 mi-crons. For use with GaAs or other infrared semi-conductor lasers, the photoresponsive material threshold should be greater than one micron. The addition of the band gap adjusting elementls) of the invention allows the tailoring of germanium alloys having the optimum band gap for the desired application.
Each of the device semiconductor alloy layers 5 can be glow discharge deposited upon the base -~4-electrode subs~rate by a conventional glow dis-charge chamber described in the aforesaid U.S.
Patent No. 4,226,898, The alloy layers also can be deposited in a continuous process. In these casesl the glow discharge system initially is evacuated to approximately 1 mtorr to purge or eliminate impurities in the atmosphere from the deposition systemO The alloy material preferably is then fed into the deposition chamber in a com~
pound gaseous form, most advantageously as fluo-rine (F2), hydrogen (H2) and germanium tetrafluo-ride (GeF~). The glow dis~harge plasma pre~erably is obtained from the gas mixture. The deposition system in U.5. Patent 4,226,898 preferably is operated at a pressure in the range of about 0.3 to 1.5 torr, preferably between 0.6 to l.Q torr such as about 0.6 torr.
The semiconductor material is deposited from a self-sustained plasma onto the substrate which ~0 is heated, preferably by infrared means to the desired deposition temperature for each alloy layer~ The doped layers of the devices are de-posîted at various temperatures in the range of 200C ~o about 1000C, depending upon the form of 5 the material used. The upper limitation on the substrate temperature in part is due to the typeof metal substrate utilizedO For aluminum the upper temperature should not be above about 600C
and for stainless steel it could be above about 10~0C. For an initially hydrogen compensated amorphous alloy to be prod~cled, such as to form the intrinsic layer in n-i-p or p-i-n devices, the substrate temperature should be less than about 400C and preferably about 300C.
The doping concentrations are varied to pro-duce the desired p, p+, n or n+ type conductivity as the alloy layers are deposited for each device.
For n or p doped layersl ~he 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. The n dopant ma-terial can be deposited at their respective opti-mum substrate temperatures and preferably to a thickness in the range of 100 ppm to over 5000 ppm for the p+ material.
The ~low discharge deposition process can include an AC signal generated plasma into which the materials are introduced. The plasma prefer-ably is sustained between a cathode and substrate anode with an AC signal of about lkHz to 13~6 MHz.

Although the band adjusting method and ele-ment(s) of the invention can be utilized in de-vices with various amorphous alloy layers, it is preferable that they are utilized with the fluo-5 rine and hydrogen compensated glow discharge deposited alloys. In this case, a mixture of gerrna-nium tetrafluo~ide and hydrogen is deposited as an amorphous compensated ~lloy material at or below about 400C, for t~e n type layer. The band ad-justed intrinsic amorphous alloy layer and the p~layer can be deposited upon the electrode layer at a hiyher substrate temperature above about 450C
which will provide a material which is fluorine compensated. For example, a mixture of the gases GeF~+H2 having ratios of 4 to 1 to 10 to 1 may be utilized. Additional fluorine may be added such as from other fluorine compounds so that the mix-ture includes up to 10% fluorine. The amount of each gas utilized may vary depending upon the other glow discharge parameters, such as temper-ature and pressure.
Although the band gap adjusting element(s) are added at least to the photoresponsive region of the devices, the element(s) also can have util-ity in the other alloy layers of the devices. As previously mentioned, the alloy layers other than the intrinsic alloy layer can be other than amor-phous 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.)

Claims (42)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A method of making an improved photo responsive amorphous alloy, said method comprising depositing on a substrate a material including a least germanium and incorpor-ating in said material fluorine as a density of states reducing element.

2. A method as defined in claim 1 further including the step of introducing at least one band gap adjusting element into said material without substantially increasing the states in the band gap to produce an alloy having a hand gap adjusted for a specified photoresponse wavelength function.

3. The method according to claim 2 wherein said adjusting element is either carbon or nitrogen.

4. The method according to claim 1 wherein said alloy is glow discharge deposited from at least a mixture of H2 and GeF4.

5. The method according to claim 4 wherein said mixture includes up to 10 per cent F2.

6. The method according to claim 4 wherein said mixture of GeF4 and H2 has a ratio of 4 to 1 to 10 to 1.

7. The method according to claim 2 wherein said alloy is deposited with an active photoresponsive region therein and said adjusting element in introduced at least in said region.

8. The method according to claim 2 wherein said method forms one step in a multi-step process for forming successively deposited alloy layers of opposite (p and n) conductivity type, the n-type layer being formed by introducing during the deposition of the layer 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 introducing during deposition of the layer a p-dopant element which is deposited with the deposited layer to produce a p-type layer.

9. The method according to claim 8 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, at least a portion of said intrinsic layer containing said adjusting element

10. The method according to claim 1 further including introducing a second density of states reducing element, said second element being hydrogen.

11. The method according to claim 10 wherein both said density of states reducing elements are incorporated into said depositing alloy substantially simultaneously.

12. The method according to claim 1 wherein said reducing element is incorporated into said alloy after deposition thereof.

13. The method according to claim 2 wherein said adjusting element is introduced into said alloy in substa-ntially discrete layers.

14. The method according to claim 2 including evaporating said adjusting element prior to introducing it into said alloy.

15. The method according to claim 14 including plasma activating said adjusting element as it is being introduced into said alloy.

16. The method according to claim 15 including activating said adjusting element by plasma activated vapor deposition.

17. The method according to claim 1 wherein said method includes 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.

18. An improved photoresponsive amorphous alloy, said alloy including germanium and incorporating flourine as a density of states reducing element.

19. The alloy according to claim 18 further including a hand gap adjusting element incorporated therein without substantially increasing the states in the gap, said alloy having a band gap adjusted for a specified photoresponsive wavelength function.

20. The alloy according to claim 19 wherein said adjusting element is either carbon or nitrogen.

21. The alloy according to claim 19 wherein said alloy has an active photoresponsive region therein and said adjusting element is included at least in said region.

22. The alloy according to claim 19 wherein said alloy is a multi-layer alloy of successively deposited layers of opposite (p and n) conductivity type, the n-type layer including an n-dopant element in the layer to produce an n-type layer and the p-type layer including a p-dopant element in the layer to produce a p-type layer.

23. The alloy according to claim 19 wherein there is deposited between said p and n doped layers and intrinsic amorphous alloy later without a p or n dopant element present therein, at least a portion of said intrinsic layer containing said adjusting element.

24. The alloy according to claim 18 further including a second density of states reducing element incorporated therein, said element being hydrogen.

25. The alloy according to claim 24 deposited by glow discharge deposition.

26. The alloy according to claim 19 including said adjusting element in substantially discrete layers.

27. The alloy according to claim 18 or 19 including at least one of an n or p conductivity portion therein, said portion including an n or p dopant element therein.

28. An improved photoresponsive device, said device comprising superimposed layers of various materials including an amorphous germanium semi-conductor alloy body having an active photoresponsive region including a band gap therein upon which radiation can impinge to produce charge carriers, said germanium amorphous alloy including fluorine as a density of states reducing element.

29. An improved photoresponsive device as defined in claim 28 further including a band gap adjusting element therein at least in said photoresponsive region to enhance the radiation absorption thereof without substantially increasing the states in the gap, the band gap of said alloy being adjusted for a specified photoresponse wavelength function.

30. The device according to claim 29 wherein said adjusting element is carbon.

31. The device according to claim 29 wherein said alloy body is a multi-layer body formed of successively deposited layers of opposite (p and n) conductivity type, the n-type layer being formed by introducing during the deposition of the layer 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 introducing during deposition of the layer a p-dopant element which is deposited with the deposited layer to produce a p-type layer.

32. The device according to claim 31 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, at least a portion of said intrinsic layer containing said adjusting element.

33. The device according to claim 28 further including a second density of states reducing element incorporated therein, said element being hydrogen.

34. The device according to claim 33 depos-ited by glow discharge deposition.

35. The device according to claim 29 wherein said alloy body includes said adjusting element in substantally discrete layers.

36. The device according to claims 28, 29 or 30 wherein said alloy body includes at least one of an n or p conductivity region therein, said region including an n or p dopant element therein.

37. The device according to claims 28, 29 or 30 wherein said alloy body forms part of a Schottky barrier solar cell.

38. The device according to claims 28, 29 or 30 wherein said alloy body forms part of an MIS solar cell.

39. The device according to claims 28, 29 or 30 wherein said alloy body forms part of a p-n junction device.

40. The device according to claims 28, 29 or 30 wherein said alloy body forms part of a p-i-n device.

41. The device according to claims 28, 29, or 30 wherein said alloy body forms part of a photo-detector.

42. The device according to claims 28, 29 or 30 wherein said alloy body forms part of an electrostatic image producing device.