AN AMORPHOUS SILICON MATERIAL FABRICATED BY A MAGNETICALLY ALIGNED GLOW DISCHARGE

Abstract: An amorphous silicon material and devices fabricated of two deposited layers of silicon, the two layers having opposite spin orientation. The deposition is made under the influence of a magnetic field for the first layer and the opposite magnetic field for the second layer. Apparatus suitable for forming devices according to the process of the invention comprises: (a) heating element means (20) for holding at least one substrate (55) on which the semiconductor layers are formed; (b) a first electrode (22) for forming a glow discharge; (c) a second electrode (34) for forming the glow discharge opposed to said first electrode; (d) power supply means (60) for supplying power to said first electrode and said second electrode to form said glow discharge; (e) magnetic field producing means (30) adjacent said substrate holder for producing a first magnetic field with a first orientation at said substrate holder; (f) means for reversing said magnetic field to produce a second magnetic field with a second orientation at said substrate holder; (g) a chamber (15) for holding said substrate holder, first electrode, and second electrode; (h) means (40) communicating with said chamber for forming a vacuum in said chamber; and (i) means (45) communicating with said chamber for passing a gas containing the material to be formed on the substrate into the chamber.

Description: AN AMORPHOUS SILICON MATERIAL FABRICATED BY A MAGNETICALLY ALIGNED GLOW DISCHARGE Background of the Invention The present Invention is directed towards a method for the production of low cost thin films of semiconductors such as the amorphous silicon type. In the world's search for a non-polluting re¬ newable energy source, it has become apparent that silicon photovoltaic devices can play a major role if the cost for producing the cells can be reduced to a competitive level. State-of-the-art photovoltaics work well, but are energy intensive when compared with conventional energy sources. Amorphous silicon cells of the photovoltaic variety, amorphous semi-conductor electronic circuits, and * amorphous photo-reproductive films may overcome many of the problems with conven¬ tional silicon mateirals; however, until recently they have only remained lab experiments due to the many technical problems associated with their construction. To date, the size of experimental amorphous cells has been extremely small due to defects and short circuits In the cell. Summary of the Invention Amorphous silicon has many advantages as a photovoltaic material. It has a short range order of no more than 20 A (angstrom units) and an average den- sity of localized states in the energy gap of 10 17 cm " or less. Glow discharge amorphous silicon has a drift mobility of electrons of 10 J cm /V-sec. or greater. It has been estimated that an electron lifetime of 10 ϊ seconds is obtainable. O The apparatus herein described makes use of mag¬ netic means to help.align the silicon deposits. It has also been found tha the magnet's Influence greatly increases the deposition rate and helps to prevent contaminnation from the chamber walls. The use of magnetic means has also been found to create a novel improved junction. Brief Description of the Drawings Figure 1 Is a view of a first apparatus for the production of amorphous silicon devices. Figure 2 is a cross sectional view of a first embodiment of the silicon device. Figure 3 is a view of a second apparatus for the production of amorphous silicon devices. Figure 4 is a cross sectional view of a second embodiment of an amorphous silicon device. Figure 5 Is a cross sectional view of a third embodiment of an amorphous silicon device. Figure 6 is a cross sectional view of a fourth embodiment of an amorphous silicon device. Figure 7 is a view of a third apparatus for the production of amorphous silicon devices. Figure 8 is a cross sectional view of fifth em¬ bodiment of an amorphous silicon device. Figure 9 is a cross sectional view of a sixth embodiment of an amorphous silicon device. Detail Description of the Invention The present invention relates to a novel elect¬ ronic silicon device and method for producing same. Referring to Figure 1, a first embodiment of an elec¬ tronic silicon production device of the present inven- \ OM ~ tion is designated as 5. The production device 5 is a glow discharge app¬ aratus suitable for the production of the electronic silicon devices of Figure 2. The glow discharge device consists of a vacuum chamber 15 and a heating element 20. The heating element 20 is attached to a magnet core means 30. The core means 30 also serves as an electrode 22. Electrode 34 is located at a spaced distance from electrode 22, which consists of a ring coil, or screen. Outlet 40 is connected to a suitable high vacuum pump means, i.e., mechanical, diffusion, ion, or cryogenic, for the evacution of 15. While the highest level of vacuum or purity in the vacuum chamber is desirable, it has been shown that a mechanical low vacuum system can produce working cells. Inlet 45 allows for the introduction of gases to the chamber 15. Sensors 50 allow for the monitor¬ ing of pressure inside chamber 15. Such sensor means are well known to the art and usually consist of a thermocouple, hot filament, or ionization type gauge. Usually two types of sensors are used together to cover the full vacuum range. A substrate 55 is placed on heating element 20. The substrate means .is comprised of an electrically conducting metal, such as for example steel, aluminum, gold, silver, etc. It is usually advisable to coat the heating element with a layer of a material such as antimony to provide uniform heat conduction to the substrate. A power supply 60 which can be A.C. (alternating current), D.C. (direct current), or R.F. (radio fre¬ quency), is connected to 34 and 22. If D.C. Power is used, the electrodes can be either negative or positive. However, a greater deposition rate occurs in cathodic operation, i.e., when 22 is connected to the negative side of the power supply. In operation, it has proved desirable to reverse the potential of the electrodes between the junction layers during the deposition process, though not necessary for the oper¬ ation of silicon devices. R.F. glow discharge of the type well known in the art is also possible. As shown schematically power supply 60 also energizes magnetic core means 30 and heater means 20. In operation, the chamber 15 is evacuated by vacuum pump means to a pressure approximately between 10 -2 and 10-10 torr. During evacuation, heating means 20 is energized, heating the substrate means to a tem¬ perature of about 100 degrees to 500 degrees (C). After evacuation is completed, a silicon containing gas, such as for example SiH^, silane or various form¬ ulations of silicon tetrafloride, silicon gases con¬ taining selenium, arsenic/gaseous chalcogenide glass material, or the like, is Introduced to the chamber through valve 45. When a pressure of between .1 and 150 torr has been reached, the power supply 60 is further energized to activate magnetic means 30. When the unit is thus energized in, for example, the cathodic arrangement, electrons are freed from substrate means 55. The electrons are guided by the lines f force created by magnetic means 30, thereby striking and ionizing SIHw in an orderly formulation. The SiH j , thus Ionized is attracted to the substrate and in its ionized condition is also affected by the magnetic lines of force, thus causing the SiH. molecules to be aligned on the substrate along a com¬ mon vector with a common spin rotation. The magnetic fields of force allow for a more even deposit and de¬ creases internal defects of the semiconductor which cause shortcircuits. When a sufficient deposit has been obtained, the polarity of the magnetic means 30 O is reversed. The electrodes 22 and 34 can also be reversed in polarity simultaneously. In the present mode of operation, a second layer is deposited on the first. The second layer, however, consists of SiHu of opposite vector, orientation, or spin rotation. To complete the cell, a suitable electric conducting grid 87 is evaporated onto the surface of the cell. An anti-reflecting coating may also be applied. Referring to Figure 2, a cross section of an actual cell is shown. Silicon layer 70 consists of the same material as layer 80, but is deposited with the magnetic means 30 providing an opposite spin rotation and orientation. Due to their reverse alignment an electro-static barrier 85 is created between the layers caused by the close proximity of the counter rotating fields. When photon radiation impringes on layer 70 electrons are displaced. Low energy electron are rebounded from the barrier but higher energy electrons can penetrate the boundary area 85, passing through to layer 80. This creates a polarized condition within the cell. Thus, when sub¬ strate 55 is electrically connected through a load to grid 87 useful work can be performed. While the herein mentioned cell functions at a high level of efficiency and has exhibited a number of other advantages, other materials such as germanium, cadmium, sulfide, cadmium telluride, indium phosphide, gallium, arsenide, aluminum antimonide, and other well known semi-conducting materials also show promise. While the present embodiment represents the most unique and simple method, other techniques using dopants well known to the art also have shown use with the above mentioned method. Another glow discharge apparatus is shown in Figure 3. This apparatus is quite similar to the _OM " device shown in Figure 1, having common components 34, 5, 15, 60, 50, 45, 40, 30, and 20. The main differ¬ ence is that the magnetic core 130 is not used as an electrode. Instead, a screen electrode 100 is positioned over the substrate means 55. The screen electrode consists of a suitable metal mesh with a mesh smaller than the dark space region of the cathode. The electrode 100 is positioned below the electrode means 134 and at a spaced distance above the substrate means 155 approximating the cathode dark space region. The device 105 functions differently from the device 5 in that the substrate 155 is not electrically connected to the power supply l6θ. In the device 155 the electric connection Is made to electrode 100. In operation, the power supplies. IβO energizing the electrodes and the magnet 130 are turned on. In the cathodic operating mode, the screen electrode 100 emits electrons which are influenced by the magnetic means lines of force thereby attracting positive ions. The positive ions generally pass through the screen electrode and are deposited on the substrate 155- This permits the coating of substrate materials which are not conductors of electricity although conducting materials can be coated as well. Sim¬ ilarly, the device 105 like the device 5 can operate in a reversed polarized mode as well, i.e., anodic. In Figure 4 is shown another cell type which is identical to the cell in Figure 2 except that it contains dopants, in the formation of this cell all deposition conditions remain the same except that a dopant is added to each layer. In fabrication of the photovoltaic device in Figure 4, the substrate means is placed on the heating element 20. The chamber 15 is then evacuated. Silicon containing gas is introduced along with a dopant, such as for example .1 to 10% dlborane. The power supply 60 and magnetic means 30 are then energized resulting in a deposit of P type magnetically aligned silicon 180. The chamber 15 is again evacuated and a silicon containing gas including such as for example 0.1 to 10% phoshine is introduced. The polarity of the magnet means 30 is reversed, as can be the electrode means. The power supply 60 is then energized, resulting in a deposit of N type silicon 170. A grid electrode 187 is then deposited on layer 170 by a state-of-the-art evaporation device. While the above method produces a workable cell, it has been fully contemplated to apply the layers in a reverse order. Also, while dlborane and phosphine are mentioned as dopants, it is assumed that other dopant materials well known to the art can be used as well. In Figure 5 is shown a cell of the Schottky barrier type. For its fabrication either glow dis¬ charge device herein described may be used. If the device 5 shown is used a suitable substrate 55 is placed in the chamber 15. The atmosphere is evacuated and a silicon containing gas introduced. When a suitable pressure has been obtained, the power supply • 60 and the magnetic means 30 are energized, producing a magnetically oriented deposit 300 about one micron or less in thickness. The cell is then transferred to a state-of-the-art evaporator. A thin layer of a suitable metal having a work function of around 4.5eV, such as for example, chromium, rhodium, gold, iridium, platinum, palladium, is deposited to a thickness between 80 to 150A to form layer 310. It is also possible to form a multi-layer by depositing, for example, a layer of platinim followed by a layer of silver or gold. An electrode grid 387 is then deposited over the metallic layer 310. In Figure 6 Is shown a fourth embodiment of the silicon electronic device, designated a PIN cell. In its fabrication, a doped first layer 425 about one micron or less thick is deposited on the substrate means 55 by either glow discharge device, but for the sake of discussion, we will refer to the device 5 of Figure 1. The magnetic means 30 is energized. The chamber 5 is then evacuated and silicon containing gas containing a dopant is introduced. Depending on the cell characteristic, the magnetic means 30 can be reversed in polarity, as well as the polarity of the electrode means. An undoped silicon containing gas is then introduced and an undoped amorphous silicon layer deposited about one micron or less in thickness, thereby forming intrinsic layer 450. The chamber 15 is again evacuated and a silicon containing gas in¬ cluding an opposite dopant type to layer 425 is intro¬ duced thereby depositing doped layer 475. Magnetic means 60 may be reversed as well as the polarity of the electrode means. An electrode grid 487 is then deposited, completing the cell. Another glow discharge apparatus is shown in Figure J . This device is similar to the device shown in Figure 1 and has the following common parts: 40, 22, 45, 30, 20, 50, 55, 60, 15. The device in Figure 7 differs from the device in Figure 1 by addition of second magnetic means 570 and a removable screen electrode 580 and the omission of the electrode means 34. The operation of the device in Figure 7 is identical to the devices in Figures 1 and 3 except when the magnetic means 530 is energized the magnetic means 570 is also energized, but with opposite polarity to 530. This helps to further concentrate OM the Ionic process. When the polarity of magnetic means 530 is reversed, the magnetic means 570 is likewise reversed, allowing the magnet to always be of opposite polarities, however, for certain cell configurations it may be desirable to have the magnetic polarities the same for both magnets. The removable electrode means 580 allows the device in Figure 7 to function in the mode shown in Figure 1 or Figure 3. Referring to Figure 8, a fifth embodiment of the present invention is shown. Again, the device is a silicon electronic device, such as for example, a photovoltaic cell and, more particularly, a PN junction device. The cell in Figure 8 comprises a first doped layer 625 of one conductivity type in- contact with a second doped layer 650 of opposite conductivity type, creating a junction region therebetween. For the purposes of discussion, the first layer 625 is of P type conduction with the second layer 650 N type. A third layer 675 Is of the same conduction type as the second layer 650, but contains a higher dopane concentration. The third layer 675 helps in making a better electric contact with layer 650. Completing the cell is a metal electrode lower contact means 680 and a transparent electrode upper contact means 640. The fabrication of the device in Figure 8 can be accomplished by the apparatus of Figure 3 or Figure 7. For the purpose of discussion, we will use the device in Figure 3. A glass material with a coating of such as for example, indium tin oxide 640 is placed on the heating means 120. The vacuum chamber means is then evacuated and the heating means 120 is energized, heating the substrate to between 150-600 degrees(C). O_._P A silicon contianing gas including, such .as for example, about .05 to 7 % dlborane, Is introduced to a pressure of between .05 and 150 torr. The power supply means then energizes the high voltage electrodes 100 and 134 and the magnetic means 130 for about .001 to two seconds, producing the magnetically aligned layer 625. The chamber is then re-evacuated and a silicon containing gas including between .001 and .5 percent phosphine Is introduced. The polarity of the electrode means 100 and 134 and magnteic means 130 may be reversed when forming the layer 650. Next, an additional quantity of, such as for example, phosine is introduced into the chamber means 115 so that there is between 175 and 5 % of phisphlne. The electrode means 134 and 100 and the magnetic means 130 are energized thereby producing layer 675. Completing the cell, an electrode means 680 is deposited by state-of-the-art metal evaporation equipment. Referring to Figure 9, a 6th embodiment of the present invention is shown. More, the device is a heterojunction device. The device in Figure 9 consists of a semi-conductor region 710 comprised of a material, such as for example, crystalline silicon, tin oxide, gallium arsenide, etc. The semi-conductor 710 fras a high band gap in order to be transparent to incoming solar radiation, and is highly doped. It is important and well known to those in the art that it is necessary to have a large barrier at the hetero- junction 720 In order to promote a large voltage. The barrier 720 results from the correct matching of the band struction of 710 to that of 730. The region 730 consists of a different semi-conductive material such as for example magnetically aligned amorphous silicon. Region 740 is in intimate contact with region 730. ■O Region 7^0 may consist of a layer of doped germanium or doped amorphous silicon. This layer is fabricated using glow discharge and magnetic alignment techniques herein described. The region 740 is of the same conductivity type as the region 730 but at a higher level. Completing the cell, contacts 750 and 735 are deposited by conventional deposition means. While all the present cell embodiments function well, a coating of an anti-reflecting coating improves efficiency. While all the herein mentioned cells are described as photovoltaic devices, it will be obvious to those skilled in the art that the devices herein described will also find wide utility as electronic switching devices, rectifiers or photodetectors, with minor modifications. While the invention has been herein shown and described in what is presently conceived to be the most practical and preferred embodiments thereof, it will be apparent to those of ordinary skill in the art that many modi ications may be made thereof within the scope of the invention, which scope is to be accorded the broadest interpretation of the appended claims so as to encompass all equivalent structures and devices.

Claims: I claim 1. An article of manufacture consisting of, in material part, semiconductor atoms, a substantially planar junction having a first side and a second side, and wherein: on said first side said semiconductor atoms substantially all have a spin orientation In a first direction, and on said second side said semiconductor atoms substantially all have a spin orientation in a second direction. 2. The article of claim 1 wherein the first and second directions are each substantially parallel to the plane of the junction. 3. The article of claim 2 wherein the first and second directions are at least at right angles apart. 4. The article of claim 3 wherein the first and second directions are substantially opposite from one another. » The article of claim 4 wherein the semi¬ conductor material is silicon. 6. The article of claim 5 wherein at least one dopant is present in at least one part of the silicon material. 7. An electronic gate having at least one junc¬ tion described in claim 1. 8. The gate of claim 7 wherein a first electrode Is connected to said first side and a second electrode is connected to said second side. 9. The gate of claim 7 wherein there are at least two of said junctions. 10. The semiconductor device of claim 1 further comprising a third semiconducting layer deposited above the second layer, said first, second and third layers having differing spin orientations. 11. An electronic gate comprising: (a) a substrate; (b) a first region, supported by said sub¬ strate, comprising semiconductor atoms substan¬ tially all of which have a spin orientation in a first direction; (c) a second region, immediately adjacent to said first region, comprising semiconductor atoms substantially all of which have a spin orientation in a second direction; (d) a substantially planar junction cons¬ tituting a boundary separating said first region and said second region; (e) a first electrode connected to said first region; and (f) a second electrode connected to said second region. 12. The cell of claim 11 wherein said first and second directions are each substantially parallel to said junction. 13. The cell of claim 12 wherein said first and second directions are at least at right angles. 14. The cell of claim 13 wherein said first and second directions are substantially opposite from one another. 15- The cell of claim 14 wherein said semi¬ conductor atoms are silicon. 16. The cell of claim 15 wherein at least one dopant is present in at least part of at least one region. 17. A process of making a junction in material containing semiconductor atoms, comprising the following steps: (a) evacuating a chamber in which is placed a substrate; (b) establishing a magnetic field in the vicinity of said substrate, said field being oriented in a first direction, relative to said substrate; (c) creating and maintaining a plasma in the vicinity of said substrate, said plasma containing semiconductor atoms; (d) permitting sufficient time to elapse for the deposition of a first layer of said atoms from said plasma onto said substrate; (e) changing the relative orientation of said magnetic field to said substrate, to a second direction; (f) permitting sufficient time to elapse for the deposition of a second layer of said atoms from said plasma, adjacent to said first layer, and thereby establishing a boundary region between said layers. 18. The process of claim 17 wherein said boundary region comprises a substantially planar junction. 19. The process of claim 18 wherein said first direction and said second direction are each substantially parallel to said junction. 20. The process of claim 19 wherein said directions are at least right angles apart. 21. The process of claim 20 wherein said directions are substantially opposite. 22. The process of claim 21 wherein said atoms are silicon. 23. The process of claim 17 wherein after step (d) and before step (f) a further step occurs in which a metallic film is deposited adjacent to said first layer at a portion thereof that will, after said step (f) of said claim 17, comprise said boundary. 24. The product of the process of claim 17. 25. Apparatus for forming a semiconductor device having at least two semiconductor layers formed in the presence of magnetic fields, comprising: (a) a substrate holder for holding at least one substrate on which the semiconductor layers are formed; (b) a first electrode for forming a glow discharge; (c) a second electrode for forming the glow discharge opposed to said first electrode; (d) power supply means for supplying power to said first electrode and said second electrode to form said glow discharge; (e) magnetic field producing means adjacent said substrate holder for producing a first magnetic field with a first orientation at said substrate holder; (f) means for reversing said magnetic field producing means to produce a second magnetic field with a second orientation at said substrate holder; (g) a chamber for holding said substrate holder, first electrode, and second electrode; (h) means communicating with said chamber for forming a vacuum in said chamber; and (i) means communicating with said chamber for passing a gas containing the material to be formed on the substrate into the chamber. 26. Apparatus according to claim 25, wherein said first electrode is in electrical connection with said substrate holder. 27. Apparatus according to claim 25, wherein said first electrode is positioned between said substrate holder and said second electrode. 28. Apparatus according to claim 25, further comprising a second magnetic field producing means positioned opposed to said first magnetic field producing means to provide a second magnetic field having a second orientation.

Inventors: CAMPBELL WILLIAM P III, CAMPBELL, WILLIAM, P., III
Applicants: CAMPBELL WILLIAM P III, CAMPBELL, WILLIAM, P., III
Application year: 1982
Main classification: H01L31
IPC codes: C23C16, H01L31