Title of Invention

A PRODUCTION OF DEFECT INDUCED ELECTRICAL CONTACT WITH ANTIDIFUSSION BARRIER AND A METHOD THEREOF

Abstract

The present invention is provided with a production of defect induced electrical contacts with anti-diffusion barriers comprising fabricating a photovoltaic cell (B); treating the surface layer of cadmium telluride with cadmium chloride; and depositing a layer of copper compound on cadmium telluride; depositing thereafter a top contact metallic layer on the copper compound layer to obtain the electrical contact and; characterized in that, implantation of a copper compound (B5) (CuxO/CuxN) in between CdTe (B4) and top contacting metal (B6) causes a defect induced field which enhance contacting property including a barrier for further diffusion of Top contacting material (B6) into CdTe (B4).

Full Text

FIELD OF THE INVENTION: This invention relates to a method for the production of electrical contacts and electrical contacts produced thereby. This invention further relates to a method for the production of electrical contacts with thin film p-type semiconductor class IIB-VIA compounds. BACKGROUND OF THE INVENTION: The difficulties in making good ohmic contacts top-type class II-B-VIA compounds of semiconductor such as cadmium telluride is well known. These materials on the other hand are very important for the fabrication of various electronic devices in general and photovoltaic cells in particular. As a consequence, utilisation of such material for various applications depends upon the ability to make low resistance ohmic contact on them. It is believed that the method of chemical etching of CdTe surface and consequent deposition of a thin metallic layer, the acidic etch leaves a tellurium rich surface which improves the contact between the metal to be deposited and the p-CdTe. Such chemical etching has been normally used in connection with low resistive single crystal CdTe and contact deposition is sometimes followed by a 5-15 minutes of heat treatment at 150°C in H2 atmosphere to improve the contact. From a recent report, it is evident that contact to p-CdTe can be obtained by etching the p-CdTe surface in a chemical solution like K2Cr2O7 + H2SO4 + H2O followed by Au + Cu alloy evaporation. In case of thin film p-CdTe (Thickness is less than 10 micrometers) device, one works with a relatively high resistive material (Resistivity greater than 100 Ohm-Centimeters) which makes the contact problem ever more serious. Strong acidic etching as recommended earlier is not suitable and use of dilute (1%) Br2 + CH3OH solution has been recommended. Among various techniques reported are direct applications of contact material on the fresh CdTe surface without any etching and formation of CuxTe layer on the surface by evaporation or by chemical methods. However, by far the most common technique is contact deposition after a mild Br2 + CH3OH etch. Unfortunately, the use of CuxTe layer has a tendency to be unstable and the direct applications of the contact material as well as a simple Br2 + CH3OH etch does not give electrical contacts as desired. A prior patent RE 30052 and RE 29986 disclose an invention relates to the deposition wit h lithium oxide. Hence, not relevant with instant specification. A second prior patent US4036645 discloses an invention related to deposition layer of electrically conductive material and not by any oxide. Hence, not relevant with the instant specification. A third prior patent US4067841 discloses an invention related to heat sink and not relevant with the instant specification. A fourth prior patent US5124175 discloses an invention related to a contact using tin-lead solders and not relevant with the instant specification. A fifth prior patent US4573265 discloses an invention related to dad- strip contact and not relevant with the instant specification. A sixth prior patent US4909857 discloses an invention related to electro-deposit of contacting layer for film photo voltaic cells and not relevant with the instant specification. A seventh prior patent US5059143 discloses an invention related to a mechanical contact and not relevant with the instant specification. None of the above prior patent documents focused on the defect induced electrical contact with anti-diffusion barrier. The inventor emphasizes on the production of such defect induced electrical contact in the present invention. OBJECTS OF THE INVENTION: It is therefore an object of this invention to propose a process for the production of electrical contacts, which is simple. It is a further object of this invention to propose a process for the production of electrical contacts which is cost-effective. BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS: The invention will now be explained in greater detail with the help of the accompanying drawings where Fig. 1 is a cross-sectional view of a schematic drawing of the preferred embodiment of a photovoltaic cell constructed in accordance with the present invention; Fig. 2 is a graph of current voltage characteristics of a variety of cells prepared using prior methods and the method of the present invention; Fig. 3 is a schematic diagram of the system for plasma vapor deposition. As shown in Fig. 1, the preferred embodiment of the present invention includes a first sheet (marked B1) of insulating transparent material such as glass. On sheet B1 is layer B2 of a conducting transparent material such as Indium Tin Oxide (ITO). A layer B3 is deposited over B2 and comprises an n-type wide band gap window semi conducting material such as CdS (B3) different from the semi conducting (B4) film. The layer B4 is deposited over B3. On the surface of layer B4 another layer B5 is deposited as per the present invention. The layer B5 is covered by a layer of conducting material like Ni, Au or Al marked B6. The purpose of the layer B5 is to establish proper electrical contact to B4. Fig. 3 shows the system used for carrying out the method of the present invention where 1 stands for a vacuum chamber. A pump (7) is provided to the chamber for creating vacuum in the chamber (1). A three circular electrode system (2, 3 & 4) is kept inside the vacuum chamber. The positive voltage is applied in the electrode 2 whereas the negative voltage is applied in the other two electrodes 3 & 4. A heating arrangement is kept below the center of the electrode 3 as marked 5. Using an appropriate heating arrangement, the Cu from 5. Using an appropriate heating arrangement, the Cu from 5 is evaporated through 3, 2 & 4 and allowed to be deposited over the substrates holder (6) kept in the vacuum chamber. BRIEF DESCRIPTION OF THE INVENTION: Thus according to this invention is provided a process for the production of electrical contacts, comprising fabricating a photovoltaic cell (B) and treating the surface layer with cadmium chloride (CdCI2) (B4), and depositing a layer of copper compound (B5) thereon, followed by depositing a top contact metallic layer (B6) on the copper compound layer (B5) to obtain the electrical contact (between B2 to B6). According to this invention is further provided an electrical contact comprising a photovoltaic cell (B) with a layer of a compound (B5) deposited thereon, and a top contact metallic layer (B6). In accordance with this invention is provided a process for the production of electrical contacts where the method of fabrication of the photovoltaic cell (B) using CdTe (B4) - CdS (B3) is according to known methods. Two methods of fabrication are used, a dry method and a wet method. In accordance with an embodiment, the dry method comprises depositing all the layers as described in Fig. 1 and thereafter giving the surface a treatment in CdCI2 (B4) in solution or vapour. The treated surface (B4) is then placed in a vacuum chamber (1) (Fig. 3) for deposition of CuxO layer (B5), the top contact metallic layer (B6) like Au, Ni or Al is deposited and the resulting photovoltaic cell (B) is measured with the results displayed as curves (S) in Fig. 2, which has a fill factor approximately 75%. The CuxO layer (B5) in the present invention is being fabricated using plasma vapor deposition process. The elemental Cu (5) (Fig. 3) is evaporated through an ionizing field generated through a high voltage. The system used for this purpose is depicted in Fig. 3. Before evaporation, various gases are introduced in the vacuum chamber (1) to form plasma of that particular gas. For oxide formation, O2 gas is introduced. For nitride formation, NH3 gas is introduced. The substrate holder (6) over which CuxO or CuxN are deposited as B5 is kept at a temperature in the range of 120-140°C. Deposition is continued to have thickness of the order of 0.1-03 micrometer. After that, a metallic layer like Au, Ni or Al is deposited to have final contact (B6). As a comparison with the method of the present invention, the same cell surface is treated using the chemicals mentioned earlier and metal coating like Au+Cu was deposited. The fill factor in this case is about 55 to 60%. This data indicates the superiority of the present method. A temperature cycling from -10°C to + 45°C and the light soaking at 100 mW/cm2 for 48 hrs. indicates that the contact fabrication of the present invention is much more stable compared to the conventional method. It indicates that due to innovation no further diffusion of top contacting material B6 under the influence of temperature cycling and light soaking. It is evident from the submission that the improvement in photovoltaic cell performance occurs due to the introduction of the intermediate layer of CuxO layer in between the metal coating and CdTe layer. The improvement in cell performance of the present invention is due to the introduction of defect induced field at the CdTe/metal interface. As a result, the efficiency and stability of the device is enhanced. Apart from this, the present invention depicted many of the features which clearly showed the significant advantage which the present invention achieves over the prior art. Consequently, only a few of the more outstanding features pointed out to illustrate the unexpected and unusual results obtained by the present invention. One of such features is that an intermediate thin layer of CuxO layer is initiating contact between the metal and CdTe. Moreover, the intermediate layer is very stable and unaffected with light soaking and temperature cycling. This is a unique method that can be integrated in any method of photovoltaic cell fabrication as well as in many other electronic devices fabrication. The uniqueness of this method yields better results than the conventional method. I CLAIM: 1. A production of defect induced electrical contacts with anti- diffusion barriers comprising: fabricating a photovoltaic cell (B); treating the surface layer with cadmium chloride; depositing a layer of copper compound (B5) on cadmium chloride; depositing thereafter a top contact metallic layer on the copper compound layer to obtain the electrical contact (B6) and; characterized in that, implantation of a copper compound (B5) (CUxO/CuxN) in between CdTe (B4) and top contacting metal (B6) causes a defect induced field which enhance contacting property including a barrier layer for further diffusion of Top contacting material (B6) into CdTe (B4) 2. The electrical contact as claimed in claim 1 wherein the photovoltaic cell is constructed using CdTe - CdS. 3. The electrical contact as claimed in claim 1 wherein the photovoltaic cell is fabricated by dry method and wet method. 4. The method of production of defect induced electrical contact as claimed in claim 1 comprising following steps: providing a vacuum chamber (1) containing a metal evaporator (5) and a plurality of discharge rings (2, [3 & 4]) and a means for electrical source for plasma generation; creating vacuum inside the chamber by a vacuum pump (7); introducing reactive gas (O2/NH3); energizing the plasma generator by applying electrical high voltage in between discharge rings (2 & [3,4]); characterized in that said copper vapour passes through the oxygen/Ammonia plasma layer and deposit over the photovoltaic cell on top contact metallic layer (6). 5. The method as claimed in claim 4 wherein the copper compound is such as copper oxide or copper nitride. 6. The method as claimed in claim 4 wherein the surface of photovoltaic cell is treated with cadmium chloride which is used in the form of solution or vapour. 7. The method as claimed in claim 4 wherein the elemental copper reacts with plasma of a gas such as Oxygen or Nitrogen for the formation of copper oxide or copper nitride which is deposited at a temperature of 120°C to 140°C. 8. The electrical contact as claimed in claim 1, wherein the layer of copper compound is 0.1 to 0.3 urn. 9. The electrical contact as claimed in claim 1, wherein the metallic layer is a top layer of a metal such as gold, nickel and aluminium. 10. The production of defect induced electrical contact with anti- diffusion barriers as substantially described and illustrated herein with accompanying drawing. ABSTRACT A PRODUCTION OF DEFECT INDUCED ELECTRICAL CONTACT WITH ANTI-DIFFUSION BARRIER AND A METHOD THEREOF The present invention is provided with a production of defect induced electrical contacts with anti-diffusion barriers comprising fabricating a photovoltaic cell (B); treating the surface layer of cadmium telluride with cadmium chloride; and depositing a layer of copper compound on cadmium telluride; depositing thereafter a top contact metallic layer on the copper compound layer to obtain the electrical contact and; characterized in that, implantation of a copper compound (B5) (CuxO/CuxN) in between CdTe (B4) and top contacting metal (B6) causes a defect induced field which enhance contacting property including a barrier for further diffusion of Top contacting material (B6) into CdTe (B4).

Documents:

67-KOL-2004-(02-12-2011)-ABSTRACT.pdf

67-KOL-2004-(02-12-2011)-CLAIMS.pdf

67-KOL-2004-(02-12-2011)-DESCRIPTION (COMPLETE).pdf

67-KOL-2004-(02-12-2011)-DRAWINGS.pdf

67-KOL-2004-(02-12-2011)-EXAMINATION REPORT REPLY RECIEVED.PDF

67-KOL-2004-(02-12-2011)-FORM 13.pdf

67-KOL-2004-(02-12-2011)-FORM-1.pdf

67-KOL-2004-(02-12-2011)-FORM-2.pdf

67-KOL-2004-(02-12-2011)-FORM-3.pdf

67-KOL-2004-(02-12-2011)-FORM-5.pdf

67-KOL-2004-(02-12-2011)-OTHERS.pdf

67-kol-2004-abstract.pdf

67-kol-2004-claims.pdf

67-KOL-2004-CORRESPONDENCE-1.1.pdf

67-KOL-2004-CORRESPONDENCE.pdf

67-kol-2004-description (complete).pdf

67-kol-2004-drawings.pdf

67-KOL-2004-EXAMINATION REPORT.pdf

67-KOL-2004-FORM 1-1.1.pdf

67-kol-2004-form 1.pdf

67-KOL-2004-FORM 18.pdf

67-kol-2004-form 2.pdf

67-KOL-2004-FORM 26.pdf

67-KOL-2004-FORM 3-1.1.pdf

67-kol-2004-form 3.pdf

67-KOL-2004-FORM 5-1.1.pdf

67-kol-2004-form 5.pdf

67-KOL-2004-GRANTED-ABSTRACT.pdf

67-KOL-2004-GRANTED-CLAIMS.pdf

67-KOL-2004-GRANTED-DESCRIPTION (COMPLETE).pdf

67-KOL-2004-GRANTED-DRAWINGS.pdf

67-KOL-2004-GRANTED-FORM 1.pdf

67-KOL-2004-GRANTED-FORM 2.pdf

67-KOL-2004-GRANTED-SPECIFICATION.pdf

67-KOL-2004-REPLY TO EXAMINATION REPORT.pdf

67-kol-2004-specification.pdf