Patent Application
20080203411
1. Field
Some embodiments generally relate to the conversion of solar radiation to electrical energy. More specifically, embodiments may relate to systems to improve the efficiency of manufacture and/or operation of solar radiation collectors.
2. Brief Description
A concentrating solar radiation collector may convert received solar radiation (i.e., sunlight) into a concentrated beam and direct the concentrated beam onto a small photovoltaic cell. The cell, in turn, converts the photons of the received beam into electrical current.
Prior U.S. patent application Ser. No. 11/110,611 describes several types of concentrating solar collectors. As described therein, a photovoltaic cell may be mounted to concentrating optics and electrical contacts of a solar collector using a clear adhesive (e.g., silicone) and wire bonds, respectively. A photovoltaic cell may alternatively be connected to optics by clear underfill material and to electrical contacts by flip-chip (i.e., solder ball) interconnects.
Light concentrated by the above-mentioned concentrating solar collectors must pass through the clear interfacial material prior to reception by the photovoltaic cell. These collectors are therefore susceptible to Fresnel loss and/or to yellowing of the material. Either of these phenomena can reduce the efficiency with which the collectors convert received solar radiation to electricity. Additionally, wire bonding and solder ball reflow require several intermediate steps that may decrease the efficiency and increase the cost of manufacturing.
What is needed is a system to couple an optically-active semiconductor device to an optical element that addresses one or more of the foregoing and/or other existing concerns.
To address at least the foregoing, some aspects provide a method, means and/or process steps to bias a substantially planar surface of an optically-active semiconductor device against a substantially planar surface of an optical element, and to bond the substantially planar surface of the optically-active semiconductor device to the substantially planar surface of the optical element. In some aspects, the bonding comprises heating an interface between the substantially planar surface of the optically-active semiconductor device and the substantially planar surface of the optical element.
The optically-active semiconductor device may comprise a solar cell or a light-emitting diode in some aspects. According to some aspects, the substantially planar surface of the optically-active semiconductor device comprises a substantially light-transparent material and an electrical contact, and biasing the substantially planar surface of the optically-active semiconductor device against the substantially planar surface of the optical element comprises biasing the substantially light-transparent material against a substantially light-transparent portion of the optical element and biasing the electrical contact against a conductive portion of the optical element.
The optical element may comprise a surface opposite from the substantially planar surface of the optical element and to receive light. The optical element may concentrate the received light and direct the concentrated light toward the substantially planar surface of the optical element, and the concentrated light may pass through a substantially light-transparent material of the optically-active semiconductor device and be received by the semiconductor layer.
Some aspects may provide planarizing a surface of the optically-active semiconductor device to generate the substantially planar surface of the optically-active semiconductor device, and planarizing a surface of the optical element to generate the substantially planar surface of the optical element.
In some aspects, an apparatus includes an optically-active semiconductor device and an optical element, wherein a substantially planar surface of the optically-active semiconductor device is bonded to a substantially planar surface of the optical element.
According to further aspects, the optically-active semiconductor device comprises a semiconductor substrate comprising a majority of a first type of charge carrier, a semiconductor portion comprising a majority of a second type of charge carrier, a semiconductor layer disposed between the semiconductor substrate and the semiconductor portion to generate charge carriers of the first type and of the second type in response to received photons, a first metal contact, the semiconductor portion disposed between the first metal contact and the semiconductor layer, a second metal contact in contact with the semiconductor substrate and to receive charge carriers of the second type generated by the semiconductor layer, and a substantially light-transparent material, wherein the substantially planar surface of the optically-active semiconductor device comprises a first end of the first metal contact, a second end of the second metal contact, and the substantially light-transparent material.
Alternatively to the foregoing aspect, the optically-active semiconductor device may comprise a semiconductor substrate comprising a majority of a first type of charge carrier, a first semiconductor portion comprising a majority of a second type of charge carrier, a second semiconductor portion comprising a majority of the second type of charge carrier, a semiconductor layer disposed between the semiconductor substrate and the first and second semiconductor portions to generate charge carriers of the first type and of the second type in response to received photons, a first metal contact, the first semiconductor portion disposed between the first metal contact and the semiconductor layer, a second metal contact, the second semiconductor portion disposed between the second metal contact and the semiconductor layer, a third metal contact in contact with the semiconductor substrate and to receive charge carriers of the second type generated by the semiconductor layer, and a substantially light-transparent material, wherein the substantially planar surface of the optically-active semiconductor device comprises a first end of the first metal contact, a second end of the second metal contact, and the substantially light-transparent material.
The claims are not limited to the disclosed embodiments, however, as those in the art can readily adapt the description herein to create other embodiments and applications.
The construction and usage of embodiments will become readily apparent from consideration of the following specification as illustrated in the accompanying drawings, in which like reference numerals designate like parts.
The following description is provided to enable any person in the art to make and use the described embodiments and sets forth the best mode contemplated by for carrying out some embodiments. Various modifications, however, will remain readily apparent to those in the art.
Optically-active semiconductor device 110 may comprise a solar cell (e.g., a III-V cell, II-VI cell, etc.), a light-emitting diode, and/or any other semiconductor device capable of exhibiting photon-related behavior. For example, in a case that optically-active semiconductor device 110 comprises a solar cell, device 110 may receive photons from optical element 120 and generate electrical charge carriers in response thereto. Device 110 may comprise any number of active, dielectric and metallization layers, and may be fabricated using any suitable methods that are or become known.
Optically-active semiconductor device 110 comprises substantially planar surface 115. As will be described in detail below, substantially planar surface 115 may comprise a substantially light-transparent material and one or more electrical contacts in some embodiments. Substantially planar surface 115 is bonded to substantially planar surface 125 of optical element 120.
Substantially planar surface 125 of optical element 120 may comprise a substantially light-transparent portion and one or more conductive portions according to some embodiments. In a case that substantially planar surface 115 of semiconductor device 110 comprises a substantially light-transparent material and one or more electrical contacts, the substantially light-transparent portion of surface 125 may be bonded to the substantially light-transparent material of substantially planar surface 115 and the one or more conductive portions of surface 125 may be bonded to the one or more electrical contacts of substantially planar surface 115.
Flow begins at 210, at which a substantially planar surface of an optically-active semiconductor device is biased against a substantially planar surface of an optical element. According to some embodiments, the substantially planar surface of the semiconductor device is aligned with the substantially planar surface of an optical element prior to 210. Such alignment may position elements of each planar surface adjacent to corresponding elements of the other planar surface. The alignment may proceed using any systems for aligning integrated circuit-sized features that are or become known.
According to some embodiments, alignment prior to 210 ensures that a substantially light-transparent portion of surface 125 contacts a substantially light-transparent material of substantially planar surface 115 and one or more conductive portions of surface 125 contacts one or more electrical contacts of substantially planar surface 115.
Returning to 210, biasing the substantially planar surface of the optically-active semiconductor device against the substantially planar surface of the optical element may comprise applying pressure against the semiconductor device toward the optical element and/or applying pressure against the optical element toward the semiconductor device. Biasing at 210 may serve to form a temporary bond between the two substantially planar surfaces, and may be accompanied by heat in order to form such a temporary bond. A temporary bond may also be facilitated using suitable adhesives.
Next, at 220, the substantially planar surface of the optically-active semiconductor device is bonded to the substantially planar surface of the optical element. According to some embodiments of 220, heat is applied to an interface between the substantially planar surface of the optically-active semiconductor device and the substantially planar surface of the optical element. With reference to
An amount of heat applied to the interface depends upon the composition of the substantially planar surface of the optically-active semiconductor device and the composition of the substantially planar surface of the optical element. The compositions will determine both the amount of heat that may be tolerated by the surfaces (i.e., thermal budget) as well as an amount of heat necessary to create a bond. Non-exhaustive examples of temperatures that have been deemed appropriate for bonding transparent dielectric material of an optically-active semiconductor device to transparent dielectric material of an optical element are ˜400° C. for glass frit and ˜275° C. benzocyclobutene.
The aligning, biasing and/or bonding of process 200 may proceed as described in “3D Packaging Via Advanced-Chip-To-Wafer (AC2W) Bonding Enables Hybrid System-In-Package (SIP) Integration”, S. Pargfrieder et al., Datacon Semiconductor Equipment GmbH, Radfeld, Austria. Unlike the present embodiments, however, the cited reference relates only to bonding a semiconductor chip to a semiconductor wafer.
Apparatus 400 may operate to receive light and to convert the received light to electrical current. Accordingly, optically-active semiconductor device 410 may comprise a solar cell. Device 410 includes semiconductor substrate 411 comprising a majority of a first type of charge carriers. For purposes of the present example, it will be assumed that substrate 411 comprises p+ Ge. Any other suitable substrate material may be used in conjunction with some embodiments, and the types of charge carriers associated therewith may be reversed (i.e., all p regions may be substituted for n regions and vice versa).
Semiconductor region 412 may comprise p++ Ge to improve current flow within device 410. Semiconductor layer 413 is capable of generating charge carriers (i.e., holes and electrons) in response to received photons. According to some embodiments, layer 413 comprises three distinct junctions deposited using any suitable method. According to some embodiments, the junctions are formed using molecular beam epitaxy and/or molecular organic chemical vapor deposition. The junctions may include a Ge junction, a GaAs junction, and a GaInP junction. Each junction exhibits a different band gap energy, which causes each junction to absorb photons of a particular range of energies.
Semiconductor portion 414 may comprise n++ GaAs and may support metal contact 415. Metal contact 415 may comprise any suitable metal contact, and may include an ohmic metal (e.g., Ag), a barrier contact (TiW), a solderable metal (Ni), and a passivation metal (e.g., Au). Metal contact 416 is coupled to semiconductor region 412 and exhibits a different polarity than metal contact 415 by virtue of the illustrated structure.
Optically-active semiconductor device 410 also includes anti-reflective coating 417 and substantially light-transparent material 418. Coating 417 and material 418 allow light from optical element 420 to reach semiconductor layer 413. Substantially light-transparent material 418 may comprise glass frit, benzocyclobutene or any other suitable material. The substantially planar surface of device 410 mentioned above may therefore comprise substantially light-transparent material 418, an end of metal contact 415, and an end of metal contact 416.
Optical element 420 may comprise any system to pass and/or otherwise manipulate light as desired. According to some embodiments, optical element 420 is designed to pass photons having energies which may be absorbed by semiconductor layer 413. The aforementioned substantially planar surface of optical element 420 includes substantially light-transparent material 426, an end of conductive portion 422, and an end of conductive portion 424. Substantially light-transparent material 426 may comprise any suitable material, and may be identical or different from substantially light-transparent material 418. In this regard, material 426 of optical element 420 is bonded to material 418 of device 410.
Conductive portion 422 is bonded to metal contact 416 and conductive portion 424 is bonded to metal contact 415. Accordingly, in operation, light may pass from optical element 420, through substantially light-transparent material 426, through substantially light-transparent material 418 and through anti-reflective coating 417 until being absorbed by semiconductor layer 413. Layer 413 generates charge carriers in response to the received light, which pass to metal contacts 415 and 416 and to corresponding ones of conductive portions 422 and 424. The charge carriers (i.e., electric current) are then conducted to the external circuitry to which conductive portions 422 and 424 are connected.
A substantially light-transparent material is deposited on semiconductor device 410 and optical element 420 as shown in
Next, and as also depicted in
Device 810 includes semiconductor substrate 811 comprising a majority of a first type of charge carriers. Substrate 811 comprises p+ Ge in some embodiments, but any other suitable substrate material may be used. Semiconductor region 812 may comprise p++ Ge to improve current flow within device 810, and semiconductor layer 813 is optically-active. More specifically, layer 813 is capable of generating charge carriers in response to received photons.
Semiconductor portions 814 may comprise n++ GaAs and may support metal contacts 815. Metal contact 816 is coupled to semiconductor region 817 comprising p++ Ge. Metal contact 816 exhibits a different polarity than metal contacts 815 by virtue of the illustrated structure.
Optically-active semiconductor device 810 also includes anti-reflective coating 818 and substantially light-transparent material 819. Coating 818 and material 819 allow light from optical element 820 to reach semiconductor layer 813. Substantially light-transparent material 818 may comprise glass frit, benzocyclobutene or any other suitable material. The substantially planar surface of device 810 mentioned above may therefore comprise substantially light-transparent material 818 and ends of metal contacts 815.
As shown, conductive portions 822 and 824 are bonded to metal contacts 815. Accordingly, conductive portions 822 and 824 likely exhibit a same polarity. In order for current to flow during operation, metal contact 816 may be connected to a conductive element of external circuitry that exhibits an opposite polarity and that provides an electrical path to metal contacts 815.
Core 930 includes relatively large convex surface 931, substantially flat aperture surface 932, and relatively small concave surface 933. Primary mirror 940 and secondary mirror 950 are formed on convex surface 931 and concave surface 933, respectively. An upper periphery of optical element 920 includes six contiguous facets. This six-sided arrangement may facilitate the formation of large arrays of concentrating solar collectors 900 in a space-efficient manner.
In some embodiments, core 930 is molded from low-iron glass using known methods. Core 930 may alternatively be formed from a single piece of clear plastic, or separate pieces may be glued or otherwise coupled together to form core 930.
Primary mirror 940 and secondary mirror 950 may be fabricated by sputtering or otherwise depositing a reflective mirror material (e.g., silver (Ag) or aluminum (Al)) directly onto convex surface 931 and concave surface 933. Primary mirror 940 includes conductive portion 922 disposed on a first half of convex surface 932, and conductive portion 924 disposed on a second half of convex surface 931. Gap 927 is defined between conductive portions 922 and 924 to facilitate electrical isolation thereof. Accordingly, conductive portions 922 and 924 of primary mirror 940 may create a conductive path for electrical current generated by photovoltaic cell 910. Conductive portions 922 and 924 may also, as described in above-mentioned U.S. patent application Ser. No. 11/110,611, electrically link photovoltaic cells of adjacent collectors in a concentrating solar collector array.
Primary mirror 940 also includes opening 928 within area 929. As described above with respect to other embodiments, opening 928 is filled with substantially light-transparent material 926 and area 929 is planarized during fabrication of optical element 920. A substantially planar surface of cell 910 may then be bonded to planarized area 929 as described above.
Core 930, primary mirror 940 and secondary mirror 950 may possess any shapes suitable to achieve a desired region of light concentration, as will be described below. Those skilled in the art of optics will recognize that other conic or otherwise curved surfaces may be utilized to achieve the internal reflection necessary to transmit light to photovoltaic cell 910.
The several embodiments described herein are solely for the purpose of illustration. Embodiments may include any currently or hereafter-known versions of the elements described herein. Therefore, persons skilled in the art will recognize from this description that other embodiments may be practiced with various modifications and alterations.
