CA1192817A - Method for increasing the band gap in photoresponsive amorphous alloys and devices - Google Patents

Abstract

ABSTRACT

The production of improved photoresponsive amorphous alloys (118, 146, 148, 150, 168, 170, 172, 174, 176, 180, 194, 206, 208, 210, 214, 216, 218, 220) and devices (142, 168, 178, 192, 198, 212), such as photovoltaic, photoreceptive devices and the like; having improved wavelength threshold characteristics is made possible by adding one or more band yap increasing elements to the alloys (118, 146, 148, 150, 168, 170, 172, 174, 176, 180, 194, 206, 208, 210, 214, 216, 218, 220) and de-vices (142, 168, 178, 192, 198, 212). The in-creasing element or elements are added at least to a portion of the active photoresponsive regions (150, 170, 172, 180, 186, 194, 208, 216) of amor-phous devices (142, 168, 178, 192, 198, 212) con-taining silicon and fluorine, and preferably hy-drogen. One adjusting element is carbon which increases the band gap from that of the materials without the adjusting element incorporated there-in. Other increasing elements can be used such as nitrogen. The silicon and increasing elements are concurrently combined and deposited as amorphous alloys (118, 146, 148, 150, 168, 170, 172, 174, 176, 180, 194, 206, 208, 210, 214, 216, 218, 220) by vapor deposition, sputtering or glow discharge decomposition. The addition of fluorine bonding and electronegativity to the alloy (118, 146, 148, 150, 168, 170, 172, 174, 176, 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 band gap increasing element(s) to be added to the alloy (118, 146, 148, 150, 168, 170, 172, 174, 176, 180, 194, 206, 208, 210, 214, 216, 218, 220) to adjust the band gap without reducing the electronic qualities of the alloy (118, 146, 148, 150, 168, 170, 172, 174, 176, 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 compensating or altering element(s) can be added during deposition of the alloy (118, 146, 148, 150, 168, 170, 172, 174, 176, 180, 194, 206, 208) 210, 214, 216, 218, 220) or following deposition.
The addition of the increasing element(s) to the alloys (118, 146, 148, 150, 168, 170, 172, 174, 176, 180, 194, 206, 208, 210, 214, 216, 218, 220) increases the band gap to a widened utilization width for a particular device (142, 168, 178, 192, 198, 212) to increase the photoabsorption effi-ciency and to thus enhance the device's photo-responseness without adding states in the gap which decrease the efficiency of the devices (142, 168, 178, 192, 198, 212). The band gap increasing element(s) can be added in varying amounts, in discrete layers or in substantially constant amounts in the alloys (118, 146, 148, 150, 168, 170, 172, 174, 176, 180, 194, 206, 208, 210, 214, 216, 218, 220) and devices (142, 168, 178, 192, 198, 212).

Description

9~6 This invention relates t:o a method of making amorphous alloys having an increased band gap and devices made therefrom. The invention has i~s mos~ important application in making improved photoresponsive alloys and devices having large band gaps at least in a portion thereof for spe--cific ~hotoresponsive applications including pho-toreceptive devices such as solar cells of a p-i-n, p-n, Schottky or MIS (metal-insulator-semicon~

ductor) type; photoconducting medium such as uti-lized in xerography; photodetecting devices and photodiodes including large area photodiode ar-raysO
Silicon is the ba~is of the huge crystalline semiconductor industry and is the material which has produced expensive 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 devicemanufacturing industry. This was due to the abil-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.

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This was accomplished by diffusing into such crys-talline material parts per million of donor (n~ or acceptor (p) dopant materials introduced as substitutiona] impurities into the substantially pure crystalline materials, to increase their electrical conductivity and to control their being either of a p or n conduction type. The fabri cation processes for making p-n junction crystals involve extremely complex, time consuming, and expensive procedures. Thus, these crystalline materials useful in solar cells and current con-trol devices are produced ~nder very carefully controlled conditions b~ ~rowing individual sinyle silicon or germanium crystals, and when p-n junc-tions are required, by doping such single crystalswith 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 crystal---2~

line material, have all resulted in an impossible economic barrier to the large scale use of crys-talline semiconductor solar cells for energy con-version. Further, crystalline silicon has an indirect optical edge which results in poor liqht absorption in the material. Because of the poor light absorption, crystalline solar cells have to be at least 50 microns thick to absorb the inci-dent sunlight. Ev~n if the sin~le crystal mate-rial is replaced by polycrystalline silicon withcheaper production processes, the indi~ect optical edge is still maintained; hence the material thickness is not reduced The polycrystalline material also involves the addition o grain boundaries and other problem defects.
An additional shortcoming of the crystalline material, for solar applications, is that the crystalline silicon band gap of about 1.1 eV in-herently is below the optimum band gap of about ~ 1.5 eV. The admixture of germanium, while pos-sible, further narrows the band gap which further decreases the solar conversion efficiency.
In summary, crystal silicon devices have fixed parameters which are not variable as de-sired, require large amounts of material, are only . 8 J~

producible in relatively small areas and are ex-pensive and time consuming to produce. Devices based upon amorphous silicon can eliminate these crystal silicon disadvantages. Amorphous 5il icon has an optical absorption edcle having properties similar to a direct gap semiconductor and only a material thickness of one micron or less is neces-sary to absorb the same amount of sunlight as the 50 micron thick ~rystalline siliccn. Further, amorphous silicon can be made faster, easier and in larger areas than can crystal silicon.
Accordingly, a considerable effort has been made to develop processes for readily depositing amorphous semiconductor alloys or films, each of which can encompass relatively large areas, if desired, limited only by the si~e 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 coun-terparts. For many years such work was substan-tially unproductive. Amorphous silicon or ger-manium (Group IV) films are normally four-fold coordinated and were found to have microvsids and S dangling bonds and other defects which produce a high density o~ localized states in the energy gap -thereof. The presence of a high density of local-ized states in the energy gap o amorphous silicon semiconductor films results in a low degree of 5 photocQnductivity and short carrier lietlme, making such films unsuitable for photoresponsive applications. Additionally, such films cannot be successfully doped or otherwise modified to shift the Fermi level cl~se to the conduction or valence bands, making them unsuitable for making p-n junc-tions for solar cell and current control device applications.
In an attempt to minimize the aforementioned problems involved with amorphous silicon and ger-manium, W~E. Spear and P.G. LeComber of Carnegie Laboratory o~ Physics, University of Dundee, in Dundee, Scotland, did some work on "Substitutional ~oping of Amorphous Silicon", as reported in a paper published in Solid State Communications, Vol. 17, pp. 1193-1196, 1975, toward the end of reducing the localized states in the energy gap in amorphous 5il icon or germanium to make the same approximate more closely intrinsic crystalline silicon or germanium and o substitutionally dop-ing the amorphous materials with suitable classic dopants, as in doping crystalline materials, to make them extrinsic and of p or n conduction types.
The reduction of the localizec] states was accomplished by glow discharge deposition of amor phous silicon films wherein a gas of silane (SiH~) was passed through a reaction tube where the gas was decomposed by an r.f. glow disçharge and de posited on a substra~e at a substrate temperature of about 500 600 ~ (2~7-327 C). The ma~erial so deposited on the substrate was an intrinsic amor-phous material consisting of silicon and hydrogen.
To produce a doped amorphous material a gas of phosphine (PH33 for n-type conduction or a gas of diborane (B2H6) for p~type conduction were pre-mixed with the silane gas and passed through theglow discharge reaction tube under the same oper-atiny conditions. The gaseous concentra~ion of the dopants used was between about 5 x 10-6 and 10-2 parts per volume. The material so deposited including supposedly substitutional phosphorus or boron dopant and was shown to be extrinsic and of n or p conduction type.
While it was not known by these researchers, it is now known by the work of others that the 5 hydrogen in the silane combines at an optimum temperature with many of the dangling bonds of the silicon during khe glow discharge deposition, to substantially reduce the density of the localized states in the energy gap t~ard the end of making the electronic properties of the amorphous mate-rial approximate more nearly those of the cor-respon~ing crystalline materlal.
In working with a similar method o~ glow discharge fabricated amorphous silicon solar cells utilizing silane, D.E. Carlson attempted to uti-lize germanium in the cells to narrow the optical gap toward the optimum solar cell value o~ about 1.5 eV from his best ~a~ricated solar cell mate-rial which has a band gap of 1.65-1.70 eV. (D.E.
Carlson, Journal of Non Crystalline Solids, Vol.
35 and 36 (1980) pp. 707-717, given at 8th Inter-national Conference on Amorphous and Liquid Semi-Conductors, Cambridge, Mass., Aug. 27-31, 1979).
However, Carlson has further reported that the ad-dition of germanium from germane gas was unsuc-cessful because it causes significant reductions in all of the photovoltaic parameters of the solar cells. Carlson indicated that the degradation of photovoltaic proper~ies indicates that defects in the energy gap are being created in the deposi~ed films. (D.E. Car~son, Tech. Dig. 1977 IEDM, Wash-ington, D.C., p. 214)~
In the Tech. Dig. article, above referenced, Carlson also reported the adclition of impurity gases, such as N2 and CH4. C'arlson concludes that these gases "have little effect on the photo-voltaic properties eve~ when they constitute 10~
oE the discharge atmosphere," but 30~ of CH~ causes degradation of the photovoltaic properties. No suggestion is made by Carlson that the addition of these gases can increase the band gap of the re-sulting material. Carlson does state in the first referenced article that the development of a bor-on-doped "wide band gap, highly conductive p-type material" is desirable, but made no suggestion as to which of "several additives" should be utilized to open the band gap. Carlson further stated that "there is no evidence to date that the material can be made highly conductive and p~type."
The incorporation of hydrogen in the above silane method not only has limitations based upon the fixed ratio of hydrogen to silicon in silane, but/ most importantly, various Si:H bonding con-figurations introduce new antibonding states which 5 can have deleterious consequences in these mate-rials. Therefore, there are basic limitations inreducing the density of localized states in these materials which are particularly harmful in terms of effective p as well as n cloping. ~he resulting density of states of the ~ilane deposited mate-rials leads to a narrow depletion width, which in turn limits the efficiencies of solar cells and other devices whos~ operation depends on the drift of free carriers. The method of making these materials by the use of only sil~con and hydrogen also results in a high density of surface states which affects all the above parameters. Further, the previous attempts to decrease the band gap of the material while successful in reducing the gap have at the same time added states in the ~ap.
The increase in the states in the band gap results in a decrease or total loss in photoconductivity and is thus counterproductive in producing photo~
responsive devices.
After the development of the glow discharge deposition of silicon from silane gas was carried out~ work was done on the sputter depositing of amorphous silicon films in the atmosphere of a mixture of argon (required by the sputtering depo-sition process) and molecular hydroyen, to deter-_g mine the results of such molecular hydrogen on thecharacteristics of the depos:ited amorphous silicon film. This research indicated that the hydrogen acted as a compensating agent which bonded in such a way as to reduce the localized states in the energy gap. EI~wever, the degree to which the localized states in the energy gap were reduced in khe sputter deposition process was much less than that achieved by the silane deposition process described above. The above described p and n dopant gases also were introduced in the sput-tering process to produce p and n doped materials.
These materials had a lower doping efEiciency than the materials produce~ in the glow discharge pro-cess. Neither process produced efficient p-doped materials with sufficiently high acceptor concen-trations for producing commercial p-n or p-i-n junction devicesO The n-doping efficiency was below desirable acceptable commercial levels and ~0 the p-doping was particularly undesirable since it reduced the width of the band gap and increased the number of localized states in the band gap.
The prior deposition of amorphous silicon, which has been altered by hydrogen from the silane gas in an attempt to make it more closely resemble crystalline silicon and which has been doped in a manner like that of doping crystall.ine silicon, has characteristics which in all important re-spects are inferior to those of doped crystalline silicon. Thus, inadequate doping efficiencies and conductivity were achieved especially in the p-type materialv and the photovoltaic qualities of these silicon films left much to be desired.
Greatly improved amorphous silicon alloys having significantly reduced concentrations of localized states in the energy gaps thereof and high quality electronic properties have been pre-pared by glow discharge as fully described in U.S.
Patent No. 4,226,~98, Amorphous Semiconductors Equivalent to Crystalline Semiconductors, Stanford R.
Ovshinsky and Arun Madan which issued October 7, 1980, and by vapor deposition as fully described in U.S. Patent No. 4~217~374v Stanford R. Ovshinsky and Masatsugu Izu, which issued on August 12, 1~80, 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 1uorine especially readily dif-fuses into and bonds to the amorphous silicon in the amorphous body, substantially to decrease the density of localized defect states therein, be-cause the small size of the lluorine atoms enables them to be readily introducecl into the amorphous body. The fluorine bonds to the dangling bonds oE
the silicon and forms what i'3 believed to be a partially ionic stable bond with flexible bonding angles, which results in a more stable and moLe efficient compen~a~i~n or alteration than i5 form-ed by hydrogen and other compensating or alteringagents. Fluorine is considered to be a more ef-ficient compensating or altering element than hydrogen when employed alone or with hydrogen because of its exceedingly small size, hi~h re-lS activity, specificity in chemical bonding, andhighest 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 mc>st desirably used are much greater than 5 such small percentages so as to form a silicon-8~

hydrogen-fluorine alloy. Such alloying amounts of fluorine and hydrogen may, for example, be in the range of 1 to 5 percent or greater. It i8 be-lieved that the new alloy so formed has a lower density of defect states in l:he energy gap than that achieved by the mere neutralization of dan-gling bonds and similar defect states. 5uch larger amount of fluorine, in particular, is believed to participate substantially in a new struc~ural configuration of an amorphous silicon-containing material and facilitates the addition of other al-loying materials. Fluorine, in addition to its other characteristics mentioned herein, is be-lieved to be an organizer of local structure in the silicon-containing alloy through inductive and ionic effects. It is believed that fluorine also influences the bonding of hydrogen by acting in a beneficial way to decrease the density of defect states which hydrogen contributes while acting as a density of states reducing element. The ionic role that fluorine plays in such an alloy is be-lieved to be an important factor in terms of the nearest neighbor relationships.

The non op~imum spectral response of prior art amorphous silicon photoresponsive devices is overcome in accordance with t:he present invention by adding one or more band gap increasing elements to an amorphous photoresponsive alloy at least in one or more regions thereof t:o adjust the band gap to an increased utiliæation width for particular applications without substantially increasing the deleterious states in the gap. Thus, the high quality electronic properties of the material are not suhstantially affected in forming the new increased band gap adjusted alloy~
The amorphous alloy preferably incorpora~es 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. The band gap in-creasing element(s) can be activated and may be added in vapor deposition) sputtering or glow discharge processes. The band gap can be in-creased as required for a specific application byintroducing the necessary amount of one or more of the adjusting elements into the deposited alloy in at least one region thereof. The band gap is in-creased without substantially increasing the num-

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ber of states in the band gap of the alloy and devices, because of the presence of fluorine in the alloy.
The presence of fluorine in the alloy of the invention provides a silicon alloy which differs physically, chemically and e:Lectrochemically from other silicon alloys because fluorine not only covalently bonds to the silicon but also affects in a positive manner the structural short range order of the material. This allows increasing elements/ such as carbon or nitrogen, effectively to be added to the alloy, because fluorine forms the stronger and more stable bonds than does hy-drogen. Fluorine compensates or alters silicon as well as the band increasing element(s) in the alloy more efficiently than hydrogen, because of the stron~er more thermally stable bonds and more flexible bonding configura~ions due to the ionic nature of the fluorine bonding. The use of fluo-rine produces the alloy or film, described in U.S.Patent No. 4,217,374, in which the density of states in the band gap are much lower than those produced by a combination of silicon and hydrogen, such as from silane. Since the band increasing 5 element~s) has been tailored into the material without adding substantial deleterious states,because of the influence of fluorine, the new alloy maintains high quality electronic qualities and photoconductivity when the adjusting ele-ment(s) are added to tailor the wavelength thresh-olcl for a specific photoresponse application.
Hydrogen further enhances the fluorine compensated or al~ered alloy and can be added during deposi-tion with fl-lorin~ or after deposition, as can fluorine and other alterant elements. The post deposition incorporation of hydrogen is advan-tageous when it is desired to utilize the higher deposition substrate temperatures allowed by Eluo-rine.
While the principles of this invention apply to each of the aforementioned deposition pro-cesses, for purposes of illustration herein a vapor and a plasma activated vapor deposition environment 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 silicon containing amor-phous alloy includes at least fluorine to reduce the density of states therein, to thereby allow the inclusion of one ~r more band gap increasing el~ments without substantially increasing the states in the gap. The alloy thus may have a band gap with an increased utilization width for use in various devices including, for example/ p-n and p-i-n, Schottky, or MIS solar cells, photo-detec-tors and electrostatic image producing devices.

The preferred embodiment of this invention will now be described by way of example with re-ference to the drawings accompanying this specifi-cation in which:
Fig. 1 is a dlagrammatic representation of more or less conventional vacuum deposition equip-ment to wHich has been added elements for carryi.ng out the addition of fluorine (and hydrogen) by the addition of molecular or ~luorine compounds ~on~
taining fluorine such as SiF~, and hydrogen inlets and activated fluorine and hydrogen generating units which decompose the molecular fluorine and hydrogen within the evacuated space of the vapor deposition equipment, to convert molecular fluo-rine and hydrogen to activated fluorine and hy-drogen and to direct one or both against the sub-~t~ 7 strate during the deposition of an amorphous alloycontaining silicon;
Fig. 2 illustrates vacuum deposition equip-ment like that shown in FigO 1, with activated Eluorine ~and hydrogen) ~enerating means com-prising an ultraviolet light ~ource irradiatiny the substrate during the process of depositing the amorphous alloy, such light source replacing the activat~d fluorine and hydrogen generator units shown in Fig. 1 an~ increasing element generating means;
Fig. 3 illustrates the vacuum deposition equipment for Fig. 1 to which has been added addi-tional means for doping the depositing alloy with an n or p conductivity producing material;
Fig. 4 illustrates an application wherein the deposition of the amorphous alloy and the applica-tion of the activated fluorine and hydrogen may be carried out as separate steps and in separate enclosures;
Fig. 5 illustrates exemplary apparatus for diffusing activated hydrogen into a previously deposited amorphous alloy;
Fig. 6 is a fragmentary sectional view of an embodiment of a Schottky barrier solar cell to illustrate one application of the amorphous semi-conductor photoreceptive alloys made by the pro-cess of the invention;
Fig. 7 is a fragmentary sectional view of a p-n junction solar cell device which includes a doped amorphous semiconductor alloy made by the process of the invention;
Fig. 8 is a fragment.ary sectional view of a photodetection device which includes an amorphous semiconductor alloy made by the process of the nventlon;
Fig. 9 is a fragmentary sectional view of a xerographic drum including an amorphous semi-conductor alloy made by the process of the inven-lS tion;

Fig. 10 is a fragmentary sectional view of a p-i-n junction solar cell device;
Fig. 11 is a fragmen~ary 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 amorphous alloys with the increasing element(s) of the invention incorporated therein;
and Fig. 13 is a solar spectral irradiance chart illustrating the standard sunlight wavelengths available or various photoresponsive applica--t.ions.
Referring now more particularly to Fig. 1, there is shown vapor deposition equipment general-ly indicated by reference numeral 10, which may be conventional vapor deposition equipment to which is added an activated~ compensating or altering material injecting means to be described. This equipment, as illustrated, includes a bell jar 12 or similar enclosure enclosing an evacuated space 14 in which is located one or more crucibles like crucible 16 containing the amorphous semiconductor film-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 silicon for forming an amorphous alloy con-taining silicon on the substrate 18 which, for example, may be a metal, crystalline or poly-crystalline semiconductor or other material uponwhich it is desired to form the alloy to be depo-sited by the process of the present invention~ An 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 silicon contained in the crucible 16 to evaporate the same.
A high voltage DC power supply 22 provides a suitable high voltage, for example, 10,000 volts DC, the~ positive terminal of which is connected through a control u~it 24 and a conductor 26 to the crucible 16. The negative terminal of which is connected through the control unit 24 and a conductor 28 to the filament of the electron beam source 20. The control unit 24 including relays or the like for interrupting the connection lS of thé power supply 22 to the conductors 26 and 28 when the film thickness of an alloy deposition sampling unit 30 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 includes 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
5 manual control 38 on the control panel 34 may be -~2-'7 provided to fix the desired rate of deposition of the alloy controlled by the amount of current fed to the filament of the electron beam source through a conductor 40 in a well known manner.
S irhe substrate 18 is ~a~ried on a substrate holder 42 upon which a heater 44 is mounted. A
cable 46 feeds energizing current to the heater 44 which controls the temperature of the substrate holder 42 and substrate 18 in accordance with a temperature set~ing set on a manual control 48 onthe control panel 34 of the control unit 24.
The bell jar 12 is shown extending upwardly from a support base 50 from which ~he various cables and other connections to the components within the bell jar 12 may extendO The ~upport 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 of activated fluorine or fluorine and hydrogen into 5 the bell jar 12 is regulated. Thus, if the con-2~

trol knob is set to a bell jar pressure of 10-4 Torr, the flow of fluorine or fluorine and hy-drogen into the bell jar 12 will be such as to maintain such pressure in the bell jar as the vacuum pump 56 continues to operate.
~ ources 60 and 62 of molecular fluoritle and hydrogen are shown connected through respective conduits 64 and 66 to the control unit 24. A
pressure ~ensor 6~ in the bell jar 12 i5 connected by a cable 70 to the control unit 24. ~low valves 72 and 74 are controlled by the control unit 24 to maintain the set pressure in the bell jar. Con-duits 76 and 78 extend from the control unit 24 and pass through the suppvrt base 50 into the evacuated space 14 of tne bell jar 12. Conduits 76 and 78 r~spectively connect with activated fluorine and hydrogen generating units 80 and 82 which convert the molecular fluorine and hydrogen respectively to activated fluorine and hydrogen, ~ which may be atomic and/or ionized forms of these gases. The activated f`luorine and hydrogen gen-erating units 80 and 82 can be heated tungsten filaments which elevate the molecular gases to their decomposition temperatures or a plasma gen-erating uni.t well known in the art for providing a plasma of decomposed gases. Also, activated fluo-rine and hydrogen in ionized forms Eormed by plas-ma can be accelerated and injected into the de-positing alloy by applying an electric field be-S tween the substrate and the activating source. Ineither event, the activated fluorine and hydrogen generator units 80 and 82 are preferably placed in the immediate vicinity of the substrate 18, so that the relativel~ ~hort-lived activated fluorine and hydrogen delivered thereby are immediately in-jected into the vicinity of the substrate 18 wherethe alloy is depositing. The activated fluorine or fluorine and hydrogen ~s well as other com-pensating or altering elements also can be pro-duced from compounds containing the elements in-stead of from a molecular gas source.
As previously indicated, to produce usefulamorphous alloys which have the desir~d charac~

teristics for use in photoresponsive devices such as photoreceptors, solar cells, p-n junction cur-rent control devices, etc.~ the compensating oraltering agents, materials or elements produce a very low density of localized states in the energy gap without changing the basic 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-sure in the bell jar by ad~u~sting the size of the outlet of the generator.
The temperature of the substrate 18 is ad-justed to obtain the maxim~m reduction in the density of the localized states in the energy gap of the amorphous alloy involved. The substrate surface temperature will genera].ly be such that it ensures high mobility of the depositing materials;
and preferably one belo~ the crystalliæation tem-perature of the depositing alloy.
The surface of the substrate can be irra-diated by radiant energy to further increase the mobility of the depositinq alloy material, as by mounting an ul~raviolet 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 5 the substrate 18. This ultraviolet light will decompose the molecular fluorine or fluorine andhydrogen both spaced from and at the substrate 18 to form activated fluorine (and hydrogen) which diffuses into the depositing amorphous alloy con-densinq on the substrate 18. The ultravioletlight also enhances the surface mobility of the depositing alloy materlal.
In Figs. 1 and 2, the band gap increasing elements can be added in gaseous form i~ an iden-tical fashion to the fluorine and hydrogen byreplacing the hydrogen generator 82 or by adding one or more activated increasing element gene-rators 86 and 88 (Fig. 2). Each of the generators 86 and 88 typically will be dedicated to one o the increasing elements such as carbon or nitro-gen. For example, the generator 86 could supply carbon as in the form of me~hane gas (CH4).
Referring now to Fig. 3, it is illustrated the 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 intrinsisally modest n-type alloy a more substantially n-type alloy, and then a p-S dopant like aluminum, gallium or indium may be-27-2~:~'7 added to form a good p-n junction within the al-loy. A crucible 90 is shown for receiving a dop~
ant like arsenic which is evaporated by bombarding the same with an electron beam source 92, like the beam source 20 previously de~3cribed. The rate at which the dopant evaporates :into the atmosphere of the bell jar 12, which is determined by the in-tensity of the ele~tron beam produced by the elec-tron beam source 9~, i5 set by a manual control 94 on the control panel 34, which controls the cur~
rent fed to tlle filament forming part of this beam source to produce the set evaporation rate. The evaporation rate is measured by a thickness sampl-i~g unit 96 upon which the d~pant material de-posits and which generates a signal on a cable 98extending 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 silicon and the n-conductivity dopant is terminated and the cru-cible 90 (or another crucible not shown) is pro-vided with a p conductivity dopant described, and the amorphous alloy and dopant deposition process ~3~

then proceeds as before to increase the thickness of the amorphous alloy with a p-conductivity re-gion therein.
The band increasing element~s) also can be added by a similar process to that described for the dopant by utilizing another crucible similar to t:he crucible 90.
In the case where the amorphous alloys com-prise two or more elements which are s~lid at room temperature, then it is usually desirable to sepa~
rately vaporize each element placed in. a separate crucible, and control the deposition 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 thickness and composition of the depositing alloy.
While activated fluorine (and hydrogen) are believed to be the most advantageous compensating agents for use in compensating amorphous alloys including siliconl in accordance with broader aspects of the invention, other compensating or altering agents can be used. For example, oxygen may be use:Eul in reducing the density of localized states in the energy gap when used in small amounts _~9_ so as not to change the intrinsic characteristic of the alloy.
As previously indicated, altho~gh it i5 pre-ferred that compensating and other agents be in-corporated into the amorphous alloy as it is de-posited, in accordance with ano~her aspect of the lnventiorl, the amorphous alloy deposition process and the pro¢ess of injecting the compensating and other agents into the semiconductor all~y can be done in a completely separate environment from the depositing of the amorphous alloy. This can have an advantage in certain applications since the conditions for injecting such agents are then completely independent ~f the conditions for the alloy deposition. Also, as previously explained, if the vapor deposition process produces a porous alloy, the porosity of the alloy, in some cases, is more easily reduced by environmental conditions quite different from that present in the vapor deposition process. To this end, reference should now be made to Figs. 4 and 5 which illustrate that the amorpho~s deposition process and the com-pensating or altering agent diffusion process are carried out as separat~ steps in completely dif-ferent envi:ronments, Fig. 5 illustrating appara~us

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for carrying out the post compensation diffusion process.
As there shown, a low pressure container body 100 is provided which has a ;Low pressure chamber 102 having an opening 104 at the top thereof.
This openirlg 104 is close~ by a cap 106 having threads 108 which thread around a corresponding threaded portion on the exterior of the ontainer body 100. ~ sealing O-ring 110 is sandwiched between the cap 106 and the upper face of the container body. A sample-holding electrode 112 is mounted on an insulating bottom wall 114 of the chamber 100. A sub~trate 116 upon which an amor-phous semiconductor alloy llB has already been deposited is placed on the electrode 112. The upper face of the substrate 116 contains the amor-phous alloy 118 to be altered or compensated in the manner 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 12~ which supplies a voltage between the electrodes 112 and 120 to provide an activated plasma of the compensating or altering gas or 5 gases, such as fluorine, hydrogen, and the like, fed into the chamber 107. For purposes of sim-plicity, Fig. 5 illustrates only molecular hydro-gen being fed into the chamber 102 by an inlet conduit 128 passing through t:he cap 106 and ex-tending from a supply tank 1-l0 of molecular hydro-gen. Other compensating or altering gases (such as fluorine and the like) also may be similarly fed into the chamber 102. The conduit 128 is shown connected to a valve 132 near the tank 130.
A flow rate indica~ing gauge 134 is shown con-nected to the inlet conduit 128 beyond the valve 132.
Suitable means are provided for heating the interior of the chamber 102 so that the substrate temperature is elevated pref~rably to a temper-ature below, but near the crystallization temper-ature of the film 118. For e~cample, coils of heating wire 136 are shown in the bottom wall 114 of the chamber 102 to which coils connect a cable (not shown) passing through the walls of the con-tainer body 100 to a source of current for heating the same.
The high temperature togethér with a plasma of yas contai.ning one or more compensating ele-ments developed between the electrodes 112 and 120 ~32-'7 achieve a reduction of ~he localized states in the band gap of the alloy. The compensating or alter-ing of the amorphous alloy 1.18 may be enhanced by irradiating the amorphous al.loy 118 with radiant energy from an ultraviolet l.ight source 138, wh.ich is shown outside of the container body 100 di-recting ultraviolet light between the elec-trodes 112 and 120 through a quartz window 140 mounted in the side wall of the container body 100.
The low pressure or vacuum in the chamber 102 can be developed by a vacuum pump (not shown) such as the pump 56 in Fig. 1. f~he pressure oE the chamber 102 can be on the order of O3 to 2 Torr with a substrate temperature on the order of 2Q0 to 450C. ~he activated fluorine (and hydrogen) as well as other compensating or altering elemen~s 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. Further, the alloys and devices of the pre sent invention can be utilized with or in other devices or configurations such as, for example, in a multiple cell device.

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 o~ making an ohmic contactwith an amorphous alloy 146 compensated or altered to provide a low density of localized states in the energy gap and with a band yap optimized by the processes of the present invention~ The sub-strate 144 may comprise a low work function metal,such as aluminum, tantalum, stainless steel or other material matching with the amorphous alloy 146 deposited thereon which preferably includes silicon, compensated or altered in the manner of the alloys previously described. It is most pre-ferred that the alloy have a region 148 next to the electrode 144, which region forms an n~ con-ductivity, heavily doped, low resistance interface between the electrode and an undoped relatively high dark resistance region 150 which is an in-trinsic, 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 5 amorphous alloy 146 forming a Schottky barrier 154. The metallic region 152 is transparent orsemi-transparent to solar radiation, has good electrical conductivity and is of a high w~rk function (for example, 4.5 eV or greater, pro-duced, for example, by gold, platinum, palladium,etc.) relative to that oE the amorphous alloy 146.
The metallic region 152 may be a single layer of a metal or it may be a multi-layer. The amorphous alloy 146 may have a thickness of about .5 to 1 micron and the metallic region 152 may have a thickness of about 100A in order to be semi-trans-parent to solar radiation.
On the surface of the metallic region 152 is deposited a grid electro~e 156 made of a metal having good electrical conductivity. The grid may comprise orthogonally related lines of conductive material occupying only a minor portion of the area of the metallic region, the rest of which is to be exposed to solar energy. For example, the grid 156 may occupy only about from 5 to 10% of the entire area of the metallic region 152. The grid electrode 156 uniformly collects current from the metallic region 152 to assure a good low series resistance for the device.

An anti~ref.lection 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-reflectiorl layer 158 has a solar radiation incident surface 160 upon which impinges the solar radiation. For exalDple/ the anti-re-flection la~er 158 may have a thickness on the order of magnitude of the wavelength of the max-imum energy point of the solar radiation spectrum, divided by four times the index oE 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 zirco-nium oxide of about 500A in thickness with an index of refraction of 2.1.
The band increasing element(s) are added to the photocurrent generating region 150 at least in a portion thereof such as adjacent the region 152.

The Schottky barrier 154 formed at the interface between the regions 150 and 15~ enables the pho-tons from the solar radiation to produce current carriers in the alloy 146! which are collected as current by the grid electrode 15~. An oxide layer ~not shown) can be added between the layers 150 and 152 to produce an MIS (metal insulator semi-conductor) solar cell.

In addition to the Schottky barrier or MIS
solar cell shown in Fig. 6, there are solar cell constructions which utilize p-n junctions in the body of the amorphous alloy Eorming a part thereof formed in accordance with successlve deposition, compensating or altering and doping steps like that previously described. These other forms of solar cells are generically illustrated in Fig. 7 as well as in Figs. 10 and 11.
These constru~t,ions 162 generally include a transparent electrode 164 tnrough which the solar radiation energy penetrates into the body of the solar ce]l involved. Between this transparent electrode and an opposite electrode 166 is a de-posited amorphous alloy 168, preferably including silicon, initially compensated in the manner pre viously described. In this amorphous alloy 168 are at least two adjacent regions 170 and 172 where the amorphous alloy has respectively oppo-sitely doped regions, region 170 being shown as an-conductivity region and region 172 being shown as a p-conductivity region. The' doping of the regions 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. The alloy 168 has high conductivity, highly doped ohmic contact interface regions 174 and 176 of the same conductivity type as the adja-cent region of the alloy 168. The alloy regions 174 and 176 contact electrodes 164 and 166, re spectively. The increasing element(s) are added to regions 174 and also be added to region 172.
Referring now to Fig. 8, there is illustrated another applicatioh of an am~rphous alloy utilized in a photo-detector devic~ 178 whose resistance varies with the amount of light impinging thereon.
An amorphous alloy 180 thereof is band gap in-creased and compensated or altered in accordance with the invention, ha~ no p n junctions as in the e~bodiment shown in Fig. 7 and is located between a transparent electrode 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 dopedregions 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 18Q. The increasing element(s) are 5 added at least to the region 188.

LL~2~

Referring to Fig. 9 an electrostatic imageproducing device 192 (like a xerography drum) is illustrated. The device 192 has a low dark con-ductivity, selective wavelength threshold, undoped or slightly p-doped amorph~us alloy 194 deposited on a suitable substrate 196 !~uch as a drum. The increasing ele~ent(s) are added to the alloy 194 at least near the outer region thereof.
As used herein, the terms cornpensating agents or materials and altering agents, elements or materials mean materials which are incorporated in the amorphous alloy for altering or changing the structure thereof, such as, activated flucrine (and hydrogen) incorporAted in the amorphous alloy containing silicon to form an amorphous sili-con/fluorine/hydrogen composition alloy, having a desired band gap and a low density of localized states in th~ energy gap. The activated fluorine (and hydrogen) is bonded to the silicon in the alloy and reduces the density of localized states therein and due to the small size of the fluorine and hydrogen atoms they are both readily intro-duced into the amorphous alloy without substantial dislocation of the silicon atoms and their rela 5 tionships in the amorphous alloy~ This is true most particularly because of the extxeme electro~neyativity, specificityr sma]1 size and reactivity of fluorine, all of which characteristics help influence and organize the local order of the alloys. In creating this new alloy the strong inductive powers of fluorine and its ability to act as an organizer of short range order is of im-portance. The ability of fluorine to bond with both silicon and hydrogen results in the formation of new and superior alloys with a minimum of lo-calized defect states in the energy gap. Hence, fluorine and hydrogen are introduced without sub-stantial formation of other localized states in the energy gap to form the new alloys~
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 is of a width and length as desired and preferably at least 3 mils thick. The substrate has an in-sulating layer 202 deposited thereon by a conven-tional process such as chemical deposition, vapor deposition or anodizing in the case of an aluminum substrate. The layer 202 for instance, about 5 5 microns thick can be made of a metal oxide. For an aluminum substrate, 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 is a relatively fast ~position process. The elec-trode layers preferably are reflective metal elec-trodes of molybdenum, aluminum, chrome or stain-less steel for a solar cell or a photovoltaic device. The reflective electrode is preferable since, in a solar cell, non-absorbed light which passes throu~h the semiconductor alloy i5 re-flected from the electrode layers 204 where it again passes through the semiconductor alloy which then absorbs more of the light energy to increase the device efficiency.
The substrate 200 is then placed in the 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 uti-lizing the improved methods and materials of the 5 invention. Each of the devices illustrated in Figs. 10 and 11, has an alloy body haviny an over-all thickness of betwe~n about 3,000 and 30,000 angstroms. This thickness ensures that there are no pin holes or other physical defects in the structure and that there is maximum light ab-sorption efficiency. A thicker material may ab-~vrb more light, but at some thickness will not generate more current since ~he greater thickness allows more recombination of the light generated electron-hole pairs. (It should be understood that the thicknesses of the various layers shown in Figs. 6 through 11 are not drawn to scaleO) ~ eferring first to forming the n-i-p device 198, the device is formed by first depositing a heavily doped n+ alloy layer 206 on the electrode 20A. 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 of the n-i-p device 198.
While each of the devices illustrated in Figs. 10 and 11 may have other utilities, they 5 will be now described as photovoltaic devices.
-~2-Utilized as a photovoltaic device, the selectedouter p~ layer 210 is a low :Light absorption, high conductivity alloy layer. The intrinsic alloy layer 208 which can have an :increased band gap near the p~ layer 210 for ~ solar photoresponse, high light absorption~ low dark conductivity and high photoconductivity incluc3ing sufficient amounts of the increasing element(s) to widen the band gap as desired. The bottom alloy layer 204 is a low 1~ light absorption, high conductivity n+ layer. The overall device thickness ~etween the inner surface of the electrode layer 206 and the top surface of the p+ layer 210 is, as stated previously, on the order of a~ 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 intrinsic alloy 208 is preferably between about 3,000 angstroms to 30,000 angstroms.
The thickness of the top p~ contact layer 210 also is preferably between about 50 to 500 angstroms.
Due to the shorter diffusion length of the holes, the p+ layer generally will be as thin as possible on the order of 50 to 150 angstroms. Further, the outer layer (here p+ layer 210) whether n+ or p~~
will be kept as thin as possible to avoid absorp-tion of light in that contact layer.

'7 In this device as well as the p~n junctiondevice of Fig. 7, the p~ layer (174 or 210) is utilized as a contact layer and not to absorb sunlight. Therefore it should function as a win-dow to allow the sunlight to pass through to beabsoebed in the deple-tion region of the device.
In addition to makin~ the layer thin it also should have a large ban~ gap. By adding the increasing element(s) also to the region adjacent the p~
contact layer the devices increase sunlight ab-sorption and hence Jsc and also provide some in-crease in VOC. A second type of p-i~n junction device 212 is illustxated in Fig. 11. In this device a first p+ layer 214 is deposited on the electrode layer 204' followed by an intrinsic amorphous alloy layer 216 an n amorphous alloy layer 218 and an outer n~ amorphous alloy layer 220. The layers 216, 21~ and 220 each can contain ~he band gap increasing element (5) . Further, although the intrinsic alloy layer 208 or 216 (in Figs. 10 and 11) i5 an amorphous alloy the other layers are not so restricted and may be poly-crystalline, such as layer 214. (The inverse of the Figs. 10 and 11 structure not illustrated, also can be utilized.) Following the deposition of the various 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 ~por deposition envi-ronment is utilized since it is a fast deposition process. In ~his stepJ a TCO layer 222 (trans-parent conductive oxide) is added which, for exam-ple, may be indium tin oxide jITO)~ cad~ium stan-nate (Cd2SnO~, or doped tin oxide (SnO2~. TheTCO layer will be added following the post com-pensation of fluorine (and hydrogen) if the films were not deposited with one or more of the desired compensating or altering elements therein. Also, the other compensating or altering elements, above described, can be added by post compensation.
Rn electrode grid 224 can be added to either of the devices 198 or 212 if desired. For a de-vice having a sufficiently small area, the TCO
layer 222 is generally sufficiently conductive such that the grid 224 is not necessary for good device efficiency. If the device is of a suf-ficiently large area or i the conductivity of the TCO layer 222 is insufficient, the grid 224 can be 5 placed on the layer 222 to shorten the carrier path and increase the conduction efficiency of thedevices.
Referring now to Fig. 12, one embodiment of a plasma activated vapor deposition chamber 226 i9 illustrated in which the semiconductor and band increasing element(s) of the invention can be depo~ited. A control unit 228 is utilized to control the deposition parameters, such as pres-sure, flow rates, e-~c., in a manner similar to that previously described with respect to the unit 24 (Fig. l). The pressure would be maintained at about 10 3 Torr or less.
One or more reaction gas conduits, such as 230 and 232, can be u~ilized to supply gases such as silicon tetrafluoride (SiF4) and hydrogen (~12) into a plasma region 234. The plasma region 234 is established between a coil 236 fed by a DC
power supply (not illustrated) and a plate 238.
The plasma activates the supply gas or gases to supply activated fluorine (and hydrogen) to be deposited on a substrate 240. The substrate 240 may be heated to the desired deposition temper-ature by heater means as previously described.
The band increasing element(s) and silicon 5 can be added from two or more evaporation boats, -~6-such as 242 and 244. The boat 242 could for ex-ample contain carbon and the boat 244 would con-tain silicon. The elements in boats 242 and 244 can be evaporated by electroll beam or other heat~
ing means and are activated by the plasma.
If it is desired to layer the band increasing element(s) in ~he photogeneratin~ region of the film heing deposited, a shutter 246 can be uti-lizedO The shutter could rotate layering separate band increasing elements from tw~ or more of the boats or can be utilized ~o control the depositing of ~he band increasing element from the boat 242 (or others) to provide layers in the film or to vary the amount of band increasing element de-p~sited in the film. Thus, the band increasingelement(s~ can be added discretely in layers, in substantially constant or in varying amounts.
Fig. 13 illustrates the available sunlight spectrum. Air Mass 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 silicon has an indirect band gap of about 1.1 to 1.2 eV, which corresponds to the wavelength of about 1.0 micrometer (microns). This equates ~47~

to losing, i.e. not generating useful photons, for substantially all the light wavelengths above 1.0 microns. As utilized herein, band gap or E opti-cal is defined as the extrapolated intercept of a plot of (~ ~)1/2, where ~ is the absorption co-efficient and ~ L~ ~or e) is t:he photon energy.
For light having a wavelength above the threshold deEined 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.
Each of the device semiconductor alloy layers can be glow discharge deposited upon the base electrode substrate by a conventional glow dis-charge chamber described in the aforesaid U.S.
15 Patent No. 4,226,898. The alloy layers also can be deposited in a continuous process. In these cases, the glow discharge system initially is evacuated to approximately 1 mTorr to purge or eliminate impurities in the atmosphere from the deposition system. The alloy material preferably is then fed into the deposition chamber in a com-pound gaseous form, most advantageously as silicon tetrafluoride (SiF~) hydrogen (H2) and methane (CH4). The glow discharge plasma preferably is 5 obtained from the gas mixture. The deposition

-4~-system in U.S. Patent No. 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 1.0 Torr such as about 0.6 Torr.
The semiconductor mate~ial is deposited from a sel~-sustained plasma onto the substrate which is heated, preEerably by infrared means to the desired deposition temperature for each alloy layer. The doped layers of ~he devices are de-posited at various temperatures in the range of 200C to about 1000C, depending upon the form of the material used. The upper limitation on the substrate temperature in part is due to the type of metal substrate utilized. For aluminum the upper kemperature should not be above about 600C
and for stainless steel it could be above about 1000C. For an initially hydrogen compensated amorphous alloy to be produced, 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 layers, the material is doped with 5 to 100 ppm of dopant material as i~ 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 mate~
rial can be deposited at their respective optimum substrate temperatures and preferably to a thick ness in the range of 100 ppm to over 5000 ppm for the p~ material.
The glow discharge deposition can Include an AC signal generated plasma into which the mate-rials are introduced. The plasma preferably is sustained between a cathode and substrate anode with an AC signal of about lkHz to 13.6 MHz.
Although the band increasing 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-rine and hydrogen compensated glow discharge de-posited alloys. In this case, a mixture of sili-con tetrafluoride and hydrogen is deposited as anamorphous compensated alloy material at or below about 400C, for the n-type layer. The intrinsic amorphous alloy layer and the p+ layer can be deposited upon the electrode layer at a higher substrate temperature above about 450C which will provide a material which is fluorine compensated.

As previously mentioned, the alloy layersother than the intrinsic alloy layer can be other than amorphous layers, such ,as polycrystalline layers. ~By the term "amorphousil is meant an alloy or material which has long range disorder, although it may hav~ short or :intermediate order or even contaln at times som,e crystalline inclu-sions3.

Claims (40)

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 at least silicon and incorporating in said material fluorine as a density of states reducing element, and introducing at least one band gap increasing element into said material without substantially increasing the states in the band gap to produce an alloy having a hand gap with an increased utilization width.

2. The method according to claim 1 wherein said adjusting element is carbon or nitrogen.

3. The method according to claim 1 wherein said alloy is glow discharge deposited from at least a mixture of SiF4, H2 and CH4.

4. The method according to claim 3 wherein said mixture includes up to one per cent CH4.

5. The method according to claim 4 wherein said mixture of SiF4 and H2 has a ratio of 4 to 1 to 10 to l.

6. The method according to claim 1 wherein said alloy is deposited with an active photoresponsive region therein and said band gap increasing element is introduced at least in a portion of said region.

7. The method according to claim 1 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 de-position 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 de-posited layer to produce a p-type layer and where-in said band gap increasing element is introduced within a respective one of said p-type or n-type layers during the deposition thereof.

8. The method according to claim 7 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 band gap increasing element adjacent to said p or n doped layer containing said band gap increasing element.

9. The method according to claim 1 further including introducing a second density of states reducing element, said second element being hydro-gen.

10. The method according to claim 9 wherein both said density of states reducing elements are incorporated into said depositing alloy substantially simultaneously with said band gap increasing element.

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

12. The method according to claim 1 wherein said increasing element is introduced into said alloy in substantially discrete layers.

13.The method according to claim 1 including evaporating said increasing element prior to introducing it into said alloy.

14. The method according to claim 13 including plasma activating said increasing element as it is being introduced into said alloy.

15. The method according to claim 14 including activating said increasing element by plasma activated vapor deposition.

16. 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.

17. An improved photoresponsive amorphous alloy, said alloy including silicon and incorporating fluorine as a density of states reducing element therein, said alloy having a band gap increasing element incorporated therein without substantially increasing the states in the gap, said alloy having a band gap with an increased utilization width.

18. The alloy according to claim 17 wherein said band gap increasing element is carbon or nitrogen.

19. The alloy in claims 17 or 18 wherein said alloy has an active photoresponsive region therein and said band gap increasing element is included at least in a portion of said region.

20. The alloy according to claim 17 wherein said alloy is a multi-layer alloy of successively deposited layers of opposite (p and n) conduc-tivity 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, and wherein a respective one of said p-type or n-type layers contain said band gap increasing ele-ment.

21. The alloy according to claim 20 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 of a portion of said intrinsic layer containing said band gap increasing element adjacent to said p-type or n-type layer containing said band gap increasing element.

22. The alloy according to claim 17 further including a second density of states reducing element incorporated therein, said element being hydrogen.

23. The alloy according to claim 22 de-posited by glow discharge deposition.

24. The alloy according to claims 17 or 18 including said band gap increasing element in sub-stantially discrete layers.

25. The alloy according to claims 17 or 18 including at least one of an n or p conductivity portion therein, said portion including an n or p dopant element therein.

26. An improved photoresponsive device, said device comprising superimposed layers of various materials including an amorphous semiconductor alloy body having an active photoresponsive region including a band gap therein upon which radiation can impinge to produce charge carriers, said amor-phous alloy including fluorine as a density of states reducing element, said alloy further including a band gap increasing element therein at least in a portion of said photoresponsive region to enhance the radiation absorption thereof without substantially increasing the states in the gap, the band gap of said alloy being increased for enhancing the radi-ation utilization of said device.

27. The device according to claim 26 wherein the band gap of said photoresponsive region within said portion including said band gap increasing element is about 2.0 eV.

28. The device according to claim 26 wherein said adjusting element is carbon or nitrogen.

29. The device according to claim 26 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, and wherein a respective one of said p-type or n-type layers includes said band gap increasing element.

30. The device according to claim 29 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 band gap increasing element adjacent to said p-type or n-type layer containing said band gap increasing element.

31. The device according to claim 26 further including a second density of states reducing element incorporated therein, said element being hydrogen.

32. The device according to claim 31 deposited by glow discharge disposition.

33. The device according the claim 26 wherein said alloy body includes said band gap increasing element in substantially discrete layers.

34. The device according to claim 26 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.

35. The device according to any one of claims 26, 27 or 28 wherein said alloy body forms part of a Schottky barrier solar cell.

36. The device according to any one of claims 26, 27 or 28 wherein said alloy body forms part of an MIS solar cell.

37. The device according to any one of claims 26, 27 or 28 wherein said alloy body forms part of a p-n junction device.

38. The device according to any one of claims 26, 27 or 28 wherein said alloy body forms part of a p-i-n device.

39. The device according to any one of claims 26, 27 or 28, wherein said alloy body forms part of a photo-detector.

40. The device according to any one of claims 26, 27, or 28 wherein said alloy body forms part of an electrostatic image producing device.