The disclosure relates to the field of power conversion.
Power converters may be used in a number of applications to charge electronic devices, such as cell phones, audio systems, home theaters, or any other electronic devices, from a power source. It is well known in the field that Ohmic losses are inversely related to an increase in voltage and directly related to an increase in current. It is advantageous, then, to increase the fill factor of power converter devices by increasing the voltage of the devices.
Prior art power converters in the field include monolithically series-connected single layer converters made of semiconductor wafers, such as GaAs. Such power converters may be connected in series by wiring or sectored off by manufacturing the converter on a semi-insulating substrate using insulating trenches to provide electrical insulation between each sectored converter. The energy source for such power converters is a monochromatic light, such as a laser operating at a particular wavelength or energy. In this particular application, the monochromatic light is between 1 micron to 1.55 microns, in the infrared region of the spectrum. Closer to 1 micron is less advantageous for home use due to the potential dangers of the light source to the human eye, so the focus of the embodiments disclosed herein is on light sources between 1.3-1.55 microns, and in certain embodiments, around 1.3 microns. However, those skilled in the field may easily modify the invention disclosed herein to convert light of a number of wavelengths.
The invention comprises a compact, monolithic multijunction power converter, with two or more epitaxial layers of the same material stacked on top of one another with tunnel junctions in between each epitaxial layer. Because the epitaxial layers are stacked on top of one another, each epitaxial layer is thinned to collect a maximum amount of light and converts power in series to increase the fill factor by increasing voltage of the overall device and decreasing Ohmic losses (which increase with current increase). Given the stacked epitaxial layers, light which is not absorbed in one layer is absorbed in the next layer directly beneath the first layer and so on. The power converter may reach an overall efficiency of approximately 50%. There are minimal current losses in these devices given that complex circuitry is avoided using the vertical stacking of the epitaxial layers, compared to the prior art, which requires interconnections between the semiconductor light absorbing sectors.
In a first aspect, power converters are provided, comprising one or more GaInNAsSb junctions; a first semiconductor layer overlying the one or more GaInNAsSb junctions; and a second semiconductor layer underlying the one or more GaInNAsSb junctions; wherein a thickness of the one or more GaInNAsSb junctions, the first semiconductor layer and the second semiconductor layer are selected to provide a resonant cavity at an irradiated wavelength.
The drawings described herein are for illustration purposes only. The drawings are not intended to limit the scope of the present disclosure.
Reference is now made in detail to embodiments of the present disclosure. While certain embodiments of the present disclosure are described, it will be understood that it is not intended to limit the embodiments of the present disclosure to the disclosed embodiments. To the contrary, reference to embodiments of the present disclosure is intended to cover alternatives, modifications, and equivalents as may be included within the spirit and scope of the embodiments of the present disclosure as defined by the appended claims.
In certain embodiments provided by the present disclosure, two or more epitaxial layers of the same semiconductor material grown on a substrate, such as GaInNAs, GaInNAsSb, GaAs, Ge, GaSb, InP or other substrate known in the art, are stacked on top of one another with tunnel junctions in between each epitaxial layer.
In certain embodiments, three or more epitaxial layers of the same semiconductor material grown on a substrate such as GaInNAs, GaInNAsSb, GaAs, Ge, GaSb, InP or other substrate known in the art, are stacked on top of one another with tunnel junctions in between each epitaxial layer. Increasing the number of junctions in a power converter device can result in increased fill factor, increased open circuit voltage (Voc) and decreased short circuit current (Jsc). Each epitaxial layer has the same bandgap, which is roughly matched to the energy of the monochromatic light source to minimize minority carrier and thermal losses. In certain embodiments, the light source reaches the bottom most epitaxial layer closet to the substrate first. The substrate has a bandgap that is higher than the bandgap of the epitaxial layers. Given that the substrate has a higher bandgap than that of the epitaxial layers, the light source passes through the substrate and the light is absorbed by the epitaxial layers. An example of this employs GaInNAs epitaxial layers (bandgap of 0.95 eV) and a GaAs substrate (bandgap 1.42 eV). The light source in this example will not be absorbed by the GaAs substrate and will be absorbed by the GaInNAs active region. A heat sink can be coupled to the top of the uppermost epitaxial layer, and can serve to cool the device and prevent defects caused by overheating. In some embodiments, the epitaxial layer material may be a dilute-nitride material, such as GaInNAs or GaInNAsSb, or other dilute nitride known in the art. In some embodiments, the monochromatic light source has a wavelength between 1 micron and up to 1.55 microns, in certain embodiments, from 1 micron to 1.4 micron, and in certain embodiments the light source is approximately 1.3 microns. While some current may be lost through light absorption by the tunnel junction(s), light that is not collected in the first epitaxial layer can becollected in the second epitaxial layer, and so on. The overall efficiency of such a device may reach at least 50% power efficiency.
In certain embodiments, the light absorbing layer(s) comprise GaInNAsSb. In certain of the embodiments, a GaInNAsSb junction comprises Ga1-xInxNyAs1-y-zSbz, in which values for x, y, and z are 0≤x≤0.24, 0.01≤y≤0.07 and 0.001≤z≤0.20; in certain embodiments, 0.02≤x≤0.24, 0.01≤y≤0.07 and 0.001≤z≤0.03; in certain embodiments, 0.02≤x≤0.18, 0.01≤y≤0.04 and 0.001≤z≤0.03; in certain embodiments, 0.08≤x≤0.18, 0.025≤y≤0.04 and 0.001≤z≤0.03; and in certain embodiments, 0.06≤x≤0.20, 0.02≤y≤0.05 and 0.005≤z≤0.02.
In certain of the embodiments, a GaInNAsSb junction comprises Ga1-xInxNyAs1-y-zSbz, in which values for x, y, and z are 0≤x≤0.18, 0.001≤y≤0.05 and 0.001≤z≤0.15, and in certain embodiments, 0≤x≤0.18, 0.001≤y≤0.05 and 0.001≤z≤0.03; in certain embodiments, 0.02≤x≤0.18, 0.005≤y≤0.04 and 0.001≤z≤0.03; in certain embodiments, 0.04≤x≤0.18, 0.01≤y≤0.04 and 0.001≤z≤0.03; in certain embodiments, 0.06≤x≤0.18, 0.015≤y≤0.04 and 0.001≤z≤0.03; and in certain embodiments, 0.08≤x≤0.18, 0.025≤y≤0.04 and 0.001≤z≤0.03.
In certain embodiments, a GaInNAsSb junction is characterized by a bandgap of 0.92 eV and comprises Ga1-xInxNyAs1-y-zSbz, in which values for x, y, and z are: x is 0.175, y is 0.04, and 0.012≤z≤0.019.
In certain embodiments, a GaInNAsSb junction is characterized by a bandgap of 0.90 eV and comprises Ga1-xInxNyAs1-y-zSbz, in which values for x, y, and z are: x is 0.18, y is 0.045, and 0.012≤z≤0.019.
In certain embodiments, a GaInNAsSb junction is comprises Ga1-xInxNyAs1-y-zSbz, in which values for x, y, and z are: 0.13≤x≤0.19, 0.03≤y≤0.048, and 0.007≤z≤0.02.
In certain embodiments, a GaInNAsSb junction comprises Ga1-xInxNyAs1-y-zSbz, in which values for x, y, and z are selected to have a band gap that matches or closely matches the energy of the radiation used to deliver power to the device. In certain embodiments, the GaInNAsSb junction is substantially lattice matched to a GaAs substrate. It is to be noted that the general understanding of “substantially lattice matched” is that the in-plane lattice constants of the materials in their fully relaxed states differ by less than 0.6% when the materials are present in thicknesses greater than 100 nm. Further, subcells that are substantially lattice matched to each other as used herein means that all materials in the subcells that are present in thicknesses greater than 100 nm have in-plane lattice constants in their fully relaxed states that differ by less than 0.6%.
In certain embodiments, each of the epitaxial layers in the power converter is lattice matched to a GaAs substrate.
In certain embodiments, the use of layering materials of different refractive indices can produce distributed Bragg reflectors (DBR) within the structure and is used to increase the efficiency of the power converter. One such example uses a dilute nitride material, which in certain embodiments is a GaInNAsSb material, as the absorbing material in the epitaxial stack of the structure. A cavity can be grown using a material such as GaAs/AlGaAs as a DBR below the dilute nitride layer and above the substrate, and another DBR grown above the dilute nitride layer, that can be made of semiconductors or a number of oxides.
In certain embodiments, where the substrate has a higher bandgap than the absorbing material, a back-side metal can be used as structured mirror, allowing unabsorbed light to be reflected from the back metal to be reabsorbed in the epitaxial layers above. Examples of resonant cavity power converters using the double pass configuration are shown in
For use with 1 micron to 1.55 micron radiation, the mirror layer can be, for example, gold or gold/nickel alloys.
In certain embodiments, the power converter structure uses one DBR instead of two. Resonant power converters employing a single DBR are shown in
In certain embodiments, the power converter structure includes one DBR and a back mirror below the substrate. Such device configurations are shown in
In the power converters shown in
In certain embodiments, the upper most layer of the structure comprises an interface air-semiconductor above the epitaxial layers, which may comprise of one or more layers of GaInNAsSb. Below the epitaxial layer is a bottom DBR which overlays a back mirror. In these embodiments, the light hits the upper most layer of the interface air-semiconductor and moves to the epitaxial layer, then the DBR and finally reflects back through the structure after being reflected by the back mirror.
Resonant cavity configurations with two DBRs and a top substrate layer are shown in
In certain embodiments, the structure has intra-cavity contacts to avoid resistivity from the DBR structures. The contact is made in the cavity through lateral transport conducting layers (LCL) bypassing the DBR structures. Power converters having intra-cavity contacts are shown in
In certain embodiments, the structure can be grown inverted. In such cases, the substrate can be thinned down to a certain thickness or removed after growth using a variety of lift off techniques. The light passes through the substrate first before passing through the epitaxy layers. In such structures, the bandgap of the substrate is greater than the bandgap of the epitaxial layers.
Multiple photovoltaic converters comprised of a number of subcells connected in series can be constructed to increase the output voltage. The subcells can be connected in parallel for increasing output current. An example is a Pi structure as shown in
Other device structures are shown in
The power converters shown in
In certain embodiments, the two or more epitaxial layers of the same semiconductor material are of varying thicknesses. In particular, the epitaxial layers can decrease in thickness the further away from the light source. In certain embodiments, the thicknesses of each of the epitaxial layers are the same. In certain embodiments, the thicknesses of the epitaxial layers are varied, either increasing nor decreasing depending on the light source location.
In some embodiments, there is a window layer on top of the upper most epitaxial layer.
In certain embodiments, the thickness, or height, of the entire device may be between 1 micron and up to 10 microns. The area of the power converter can be, for example, between 100 microns×100 microns, and up to 1 cm×1 cm, or more. For example the total area is from 10−4 cm2 to 1 cm2. The thickness of each epitaxial layer may be between a few hundred nanometers up to a few microns.
Finally, it should be noted that there are alternative ways of implementing the embodiments disclosed herein. Accordingly, the present embodiments are to be considered as illustrative and not restrictive. Furthermore, the claims are not to be limited to the details given herein, and are entitled their full scope and equivalents thereof
This application is a Continuation of U.S. application Ser. No. 16/051,109, filed on Jul. 31, 2018, which is a Continuation of U.S. application Ser. No. 14/614,601, filed on Feb. 5, 2015, which claims the benefit under 35 U.S.C. § 119(e) of U.S. Provisional Application No. 61/936,222, filed on Feb. 5, 2014, which is incorporated by reference in its entirety.
Number | Date | Country | |
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61936222 | Feb 2014 | US |
Number | Date | Country | |
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Parent | 16051109 | Jul 2018 | US |
Child | 16521458 | US | |
Parent | 14614601 | Feb 2015 | US |
Child | 16051109 | US |