Patent Application
20240084479
Compositional grading is an epitaxial growth tool that enables access to lattice constants that differ from the substrate and minimizes defect density via controlled relaxation of mismatch strain. Compositionally graded buffers (CGBs) enable many classes of “metamorphic” III-V devices with tunable bandgaps, including multijunction solar cells, light emitting diodes, and photodetectors. CGBs are usually the thickest regions in metamorphic devices, representing a significant cost due to traditionally low deposition rates (˜5 μm/h) for multinary compounds in organometallic vapor phase epitaxy (OMVPE). Faster growth rates can increase throughput and lower cost, but dislocation dynamics models predict that threading dislocation density (TDD) is proportional to growth rate, which could unacceptably decrease material quality. Therefore, improved methods for producing better performing CGBs quickly and economically are needed.
Some embodiments are illustrated in referenced figures of the drawings. It is intended that the embodiments and figures disclosed herein are to be considered illustrative rather than limiting.
The embodiments described herein should not necessarily be construed as limited to addressing any of the particular problems or deficiencies discussed herein. References in the specification to “one embodiment”, “an embodiment”, “an example embodiment”, “some embodiments”, etc., indicate that the embodiment described may include a particular feature, structure, or characteristic, but every embodiment may not necessarily include the particular feature, structure, or characteristic. Moreover, such phrases are not necessarily referring to the same embodiment. Further, when a particular feature, structure, or characteristic is described in connection with an embodiment, it is submitted that it is within the knowledge of one skilled in the art to affect such feature, structure, or characteristic in connection with other embodiments whether or not explicitly described.
As used herein the term “substantially” is used to indicate that exact values are not necessarily attainable. By way of example, one of ordinary skill in the art will understand that in some chemical reactions 100% conversion of a reactant is possible, yet unlikely. Most of a reactant may be converted to a product and conversion of the reactant may asymptotically approach 100% conversion. So, although from a practical perspective 100% of the reactant is converted, from a technical perspective, a small and sometimes difficult to define amount remains. For this example of a chemical reactant, that amount may be relatively easily defined by the detection limits of the instrument used to test for it. However, in many cases, this amount may not be easily defined, hence the use of the term “substantially”. In some embodiments of the present invention, the term “substantially” is defined as approaching a specific numeric value or target to within 20%, 15%, 10%, 5%, or within 1% of the value or target. In further embodiments of the present invention, the term “substantially” is defined as approaching a specific numeric value or target to within 1%, 0.9%, 0.8%, 0.7%, 0.6%, 0.5%, 0.4%, 0.3%, 0.2%, or 0.1% of the value or target.
As used herein, the term “about” is used to indicate that exact values are not necessarily attainable. Therefore, the term “about” is used to indicate this uncertainty limit. In some embodiments of the present invention, the term “about” is used to indicate an uncertainty limit of less than or equal to ±20%, ±15%, ±10%, ±5%, or ±1% of a specific numeric value or target.
In some embodiments of the present invention, the term “about” is used to indicate an uncertainty limit of less than or equal to ±1%, ±0.9%, ±0.8%, ±0.7%, ±0.6%, ±0.5%, ±0.4%, ±0.3%, ±0.2%, or ±0.1% of a specific numeric value or target.
Among other things, the present disclosure relates to compositionally graded buffers (CGB) and methods and/or systems for producing CGBs. CGBs enable the growth of high quality materials that are lattice mismatched to a substrate. More specifically, the present disclosure relates to methods for making CGBs by hydride vapor phase epitaxy (HVPE). HVPE methods using a single chamber for producing a CGB may result in a transience in the CGB layers as the flows supplying the reactants are switched to produce the next subsequent layer in the CGB. In contrast to this “static” style of grading, the present disclosure describes a “dynamic” method for producing CGBs, in which multiple growth chambers are utilized. In some embodiments of the present, while growth of a first layer of a CGB is performed in the first chamber, the flow rates for the reactants needed for next layer may be set and allowed to equilibrate in the second chamber. Then, when growth of the first layer is complete, the device being synthesized, including the substrate and the first layer of the CGB may be mechanically transferred to the second chamber, where growth of the second layer of the CGB may be completed. Then, while the second layer is being deposited, the flow rates for the reactants needed to deposit the third layer of the CGB may be adjusted in the now available first growth chamber. In this fashion, a multi-layered CGB may be manufactured by repeatedly moving the substrate with the CGB back and forth between the first chamber and the second chamber until the desired structure is realized. This style of grading enables more abrupt compositional steps, a situation which is more beneficial for strain relaxation in a CGB. The concept of two separate chambers may be extended to as many chambers as there are layers in the final device stack, with a single chamber dedicated to the depositing of a single layer. So, in some embodiments of the present disclosure, a continuous HVPE system may have n chambers in series, where n corresponds to the number of layers being deposited by HVPE.
In order to bridge the difference between the lattice constant of the substrate 110 and the overlaying semiconductor layer 130, a series of individual layers 125 may be deposited on the previously presented layers 125, where each subsequent layer has a slightly different elemental composition than the prior layer, or relatively large compositional changes; e.g. from GaInP to GaInA. As described herein, these layers 125 may be deposited using a “dynamic” HVPE method, where the composition 100 is repeatedly transferred between a first chamber and a second chamber (see
In some embodiments of the present disclosure, each layer 125 of a CGB 120 of a composition 100 may include at least one of SixGe1-x, Ga1-xInxP, AlxIni-xP, AlxIni-xAs, InxGa1-xAs, GaAsP1-x, GaxIn1-xN, InAsxP1-x, and/or GaAsxSb1-x. In some embodiments of the present disclosure, a composition 100 may include at least one of a third Group III element (A3) and/or a third Group V element (B3), for example, AlGaInP, AlGaInAs, GaAsPSb, or GaAsPN.
In some embodiments of the present disclosure, each layer 125 of a CGB 120 may have a thickness between about 20 nm and about 20,000 nm resulting in a total thickness of the CGB 120 between 100 nm and about 100 μm. In some embodiments of the present disclosure, the change in x, Δx, between adjacent layers 125 (e.g. 125A and 125B) may be between about 0.01 and about 0.25 as a molar fraction basis. In some embodiments of the present disclosure, the change in lattice constant between adjacent layers 125 (e.g. 125A and 125B) may be between about 0.01 Å and about 0.25 Å. An end result of depositing a CGB 120 like those described above, may be an improved physical property and/or performance metric includes at least one of a percent strain relaxation in the cap layer 125N of a CGB 120, a density of threading dislocations in the cap layer 125N, and/or a measure of a change in concentration of an element in the CGB 120 versus thickness of the CGB 120 as measured by energy dispersive x-ray spectroscopy (EDS). In some embodiments of the present disclosure, the percent strain relaxation of the cap layer 125N may be greater than about 80% or greater than about 90% or greater than about 95%. In some embodiments of the present disclosure, the density of threading locations relaxation of the cap layer 125N may be less than about 3×10{circumflex over ( )}5 cm−2 or less than about 3×10{circumflex over ( )}6 cm−2 or less than about 3×10{circumflex over ( )}7 cm−2 or less than about 3×10{circumflex over ( )}8 cm−2.
As shown herein, an embodiment of a CGB was synthesized that included a plurality of compressive Ga1-xInxP layers with lattice constants between GaAs and InP by hydride vapor phase epitaxy (HVPE) at growth rates up to ˜1 μm/min and with threading dislocation densities (TDD) as low as 1.0×10−6 cm−2. The effect of growth conditions resulting from substrate offcut direction, growth rate, and strain grading rate on CGB quality were studied. As described above “dynamic grading” using an HVPE system was utilized to create compositional interfaces via mechanical transfer of a substrate between two growth chambers, in contrast to “static grading” where the entire CGB is manufactured in a single chamber. As shown herein, dynamic grading yields smoother grades with higher relaxation compared to static grading, possibly due to the observed formation of more abrupt interfaces. As shown herein, substrate offcut direction can be an important factor for obtaining high-quality grades with low defect density. (001) substrates offcut towards (111)B yielded smoother CGBs with lower TDD compared to CGBs grown on substrates offcut towards (111)A. Transmission electron microscopy of static and dynamic CGBs grown on A and B-offcuts only found evidence of phase separation in a static A-offcut CGB, indicating that a B offcut can help to limit phase separation, which in turn can help keep TDD low. Reduced growth rates led to the development CuPt atomic ordering, which affected dislocation glide dynamics but did not significantly alter TDD. Higher growth rates led to smoother CGBs and did not appreciably increase TDD as otherwise predicted by dislocation dynamics models. These results show, among other things, HVPE's promise for lattice-mismatched applications and low-cost InP virtual substrates on GaAs.
Described herein is a study of HVPE-grown Ga1-xInxP CGBs that bridge the lattice constant gap between GaAs and InP (3.8% mismatch), with growth rates up to −1 μm/min. The effect of growth parameters such as substrate offcut, growth rate (RG), strain grading rate (RS), and final indium fraction (xIn) on CGB defect structure were studied, with the results described herein. All materials were grown in an atmospheric pressure dual-chamber D-HVPE reactor (see
In all cases, the composition/device produced included a series of discrete steps with successively larger xIn followed by a thicker constant composition capping layer grown three times as long as the individual steps. The average RG was determined by scanning electron microscopy or TEM. High resolution x-ray diffraction (XRD) reciprocal space mapping (RSM) was used to measure the composition and residual strain (C) of the capping layer. A combination of cross-sectional TEM, CL, and ECCI was used to probe the defect structure of the CGBs and determine TDD. The TEM images presented are high-angle annular dark field (HAADF) images of either [110] or [1
An initial set of four CGBs were grown with varying substrate offcut direction and grade style at growth rates from 40-49 μm/h. In this sample set, the 4° B and 6° A substrates were co-loaded in separate static and dynamic runs. The first four rows of Table 1 list their parameters.
The TEM images exhibit the typical defect structure of step-graded buffers, with misfit dislocations generally confined to the interfaces between steps. There is evidence of gross phase separation only in the 6° A static grade, which exhibits multiple regions of contrast in the HAADF image. There are bright lines of contrast ordered near-vertically in the upper left region ‘A’, and lamellae of light and dark contrast oriented roughly parallel to the substrate/epilayer interface in region ‘B’. An EDS line-scan in region B was performed, delineated by the red arrow in
EDS was performed on the 4° B static and dynamic CGBs to understand the effect of grading style on the composition profile.
Next, CGBs with higher and lower growth rates were deposited on 4° B substrates to determine how growth rate affects CGB quality. HE577 is a static CGB grown with RG=57 μm/h, xIn of 0.95, and roughly the same strain grading rate as the initial set of samples. The TDD was 2.4×106 cm−2 and Rq=9.8 nm, showing that the grade quality has not significantly degraded despite the increase in growth rate and xIn.
HD848 and 849 are static grades with reduced growth rates of ˜20 μm/h. Reduction of the growth rate formed CuPt-type atomic ordering in these CGBs. CuPt ordering can occur in lattice-matched GaInP epilayers grown by HVPE, and can influence dislocation nucleation and glide dynamics in OMVPE-grown CGBs. CuPt ordering can create a superlattice of alternating InP and GaP {111} planes, which can be detected by diffraction. Panel a of
In addition, a dynamic CGB was grown using a reduced growth rate (HD989) to determine if dynamic grading affects ordering. xIn was 0.81, which approximately corresponds to the lattice constant required for a ˜1 eV GaInAs subcell in an optimized triple junction solar cell with GaInP top and GaAs middle junctions. This sample exhibited ordering as judged by the strong positive tilt toward [1
Variation of parameters including grading style, offcut, and growth rate all impact aspects of CGB quality. Generally, low-TDD grades were grown herein, under most conditions, but some parameters were particularly important. Dynamic grading led to reduced surface roughness and improved strain relaxation relative to static grading, but both styles achieved comparably low TDD. The substrate offcut strongly influenced CGB quality, with 4° B CGBs exhibiting improved properties vs. 6° A CGBs. The 4° B CGBs did not exhibit phase separation in any case, whereas there was phase separation in the 6° A static CGB. Order-enhanced glide was not necessary to obtain low TDD in our HVPE CGBs because CGBs grown with and without ordering exhibited low TDD. This finding suggests that some property of the B-offcut separate from, but possibly related to, the induction of ordering makes the use of B-offcuts beneficial. One possibility is that the B-offcut surface reconstruction that induces long-range ordering also limits surface diffusion and prevents phase separation, which is a surface-driven process. The prevention of phase separation is important to achieving long dislocation glide length and low TDD in graded materials.
The high growth rates employed here were not correlated with higher defect densities, even though dislocation dynamics models predict a linear dependence of TDD on both RG and RS. TDD<3×106 cm−2 was achieved for grades grown at rates from 19-57 μm/h, with no obvious degradation with higher growth rates. Notably, increasing the RS by a factor of three only led to a factor of two increase in TDD (compare HD848 vs. HD849), implying that the RS was not essential to obtaining low TDD. There is evidence that larger RG may in fact improve CGB quality by suppressing surface roughness and phase separation, which are two factors linked to higher TDD. For example, HE577, a static grade to xIn=0.96, is smoother than HD725N (static grade, xIn=0.69) despite grading to a larger lattice constant with a similar RS and being significantly thicker. This result may be attributed to the faster RG, which likely limits adatom diffusion lengths and minimizes roughening. Similarly, high RG previously was shown to prevent the formation of CuPt ordering, another process driven by surface diffusion kinetics. By extension, it may be suspected that higher HVPE RGs suppress phase separation by limiting adatom diffusion. This is supported by the fact that the dynamic 6° A CGB did not phase separate when that would normally be expected based on the offcut. This CGB does have higher TDD than any of the 4° B CGBs, suggesting that there may be some small-scale phase separation we could not detect in TEM leading to higher TDD. The static 6° A CGB did phase separate, indicating the conditions used were close to a tipping point for phase separation on 6° A and small changes in growth conditions can cause gross phase separation to occur. The combination of high growth rates and B-offcut substrates provides the best resistance to phase separation, enabling low-defect CGBs.
In summary, Ga1-xInxP CGBs were grown by HVPE on GaAs over a wide range of lattice constants between GaAs and InP, with growth rates up to −1 μm/min. TDD as low as 1.0×106 cm−2 was achieved. Substrate offcut direction strongly affected the CGB defect structure, with offcut towards (111)B planes helping to reduce TDD, surface roughness, and phase separation. Static and dynamic grading schemes were tested with slight benefit demonstrated for dynamic grading, via more abrupt compositional profiles. Higher growth rate CGBs were smoother, while lower growth rate CGBs exhibited atomic ordering and order-enhanced glide, but overall TDD did not correlate with growth rate. These results demonstrate the potential for D-HVPE to achieve significant cost reduction of metamorphic III-V devices via increased throughput and decreased capital intensity.
The present disclosure may be further understood by the following non-limiting examples:
Example 1. A composition comprising:
Example 2. The composition of example 1, wherein the alloy comprises a ternary alloy.
Example 3. The composition of example 1 or 2, wherein the alloy comprises at least one of Ga1-xInxP, InxGa1-xAs, GaAsP1-x, InAsxP1-x, or GaAsxSb1-x.
Example 4. The composition of any of examples 1-3, wherein the alloy further comprises at least one of a third Group III element (A3) or a third Group V element (B3).
Example 5. The composition of any of examples 1-4, wherein the improved physical property or performance metric includes at least one of a percent strain relaxation in a cap layer of the CGB, a density of threading dislocations in the cap layer, or a measure of a change in concentration of an element in the CGB versus thickness of the CGB as measured by energy dispersive x-ray spectroscopy (EDS).
Example 6. The composition of example 5, wherein the percent strain relaxation is greater than about 80% or greater than about 90% or greater than about 95%.
Example 7. The composition of example 5 or 6, wherein the density of threading locations is less than about 3×10{circumflex over ( )}5 cm−2 or less than about 3×10{circumflex over ( )}6 cm−2 or less than about 3×10{circumflex over ( )}7 cm−2 or less than about 3×10{circumflex over ( )}8 cm−2.
Example 8. A method for producing a compositionally graded buffer (CGB) by hydride vapor phase epitaxy (HVPE), the method comprising:
Example 9. The method of example 8, wherein:
Example 10. The method of example 9, wherein the alloy comprises a ternary alloy.
Example 11. The method of example 9 or 10, wherein the alloy comprises at least one of Ga1-xInxP, InxGa1-xAs, GaAsP1-x, InAsxP1-x, or GaAsxSb1-x.
Example 12. The method of any of examples 9-11, wherein the alloy further comprises at least one of a third Group III element (A3) or a third Group V element (B3).
Example 13. The method of claim 8, wherein at least one layer of the CGB is characterized by an improved physical property or performance metric when compared to a CGB performed by a non-HVPE method or an HVPE method using a single chamber.
Example 14. The method of example 13, wherein the improved physical property or performance metric includes at least one of a percent strain relaxation in a cap layer of the CGB, a density of threading dislocations in the cap layer, or a measure of a change in concentration of an element in the CGB versus thickness of the CGB as measured by energy dispersive x-ray spectroscopy (EDS).
Example 15. The method of example 14, wherein the percent strain relaxation is greater than about 80% or greater than about 90% or greater than about 95%.
Example 16. The method of example 14 or 15, wherein the density of threading locations is less than about 3×10{circumflex over ( )}5 cm−2 or less than about 3×10{circumflex over ( )}6 cm−2 or less than about 3×10{circumflex over ( )}7 cm−2 or less than about 3×10{circumflex over ( )}8 cm−2.
The foregoing discussion and examples have been presented for purposes of illustration and description. The foregoing is not intended to limit the aspects, embodiments, or configurations to the form or forms disclosed herein. In the foregoing Detailed Description for example, various features of the aspects, embodiments, or configurations are grouped together in one or more embodiments, configurations, or aspects for the purpose of streamlining the disclosure. The features of the aspects, embodiments, or configurations, may be combined in alternate aspects, embodiments, or configurations other than those discussed above. This method of disclosure is not to be interpreted as reflecting an intention that the aspects, embodiments, or configurations require more features than are expressly recited in each claim. Rather, as the following claims reflect, inventive aspects lie in less than all features of a single foregoing disclosed embodiment, configuration, or aspect. While certain aspects of conventional technology have been discussed to facilitate disclosure of some embodiments of the present invention, the Applicants in no way disclaim these technical aspects, and it is contemplated that the claimed invention may encompass one or more of the conventional technical aspects discussed herein. Thus, the following claims are hereby incorporated into this Detailed Description, with each claim standing on its own as a separate aspect, embodiment, or configuration.
The terms and expressions which have been employed herein are used as terms of description and not of limitation, and there is no intention in the use of such terms and expressions of excluding any equivalents of the features shown and described or portions thereof, but it is recognized that various modifications are possible within the scope of the invention claimed. Thus, it should be understood that although the present invention has been specifically disclosed by preferred embodiments, exemplary embodiments and optional features, modification and variation of the concepts herein disclosed may be resorted to by those skilled in the art, and that such modifications and variations are considered to be within the scope of this invention as defined by the appended claims. The specific embodiments provided herein are examples of useful embodiments of the present invention and it will be apparent to one skilled in the art that the present invention may be carried out using a large number of variations of the devices, device components, methods steps set forth in the present description. As will be obvious to one of skill in the art, methods and devices useful for the present methods can include a large number of optional composition and processing elements and steps.
As used herein and in the appended claims, the singular forms “a”, “an”, and “the” include plural reference unless the context clearly dictates otherwise. Thus, for example, reference to “a cell” includes a plurality of such cells and equivalents thereof known to those skilled in the art. As well, the terms “a” (or “an”), “one or more” and “at least one” can be used interchangeably herein. It is also to be noted that the terms “comprising”, “including”, and “having” can be used interchangeably. The expression “of any of claims XX-YY” (wherein XX and YY refer to claim numbers) is intended to provide a multiple dependent claim in the alternative form, and in some embodiments is interchangeable with the expression “as in any one of claims XX-YY.”
When a group of substituents is disclosed herein, it is understood that all individual members of that group and all subgroups, are disclosed separately. When a Markush group or other grouping is used herein, all individual members of the group and all combinations and subcombinations possible of the group are intended to be individually included in the disclosure. For example, when a device is set forth disclosing a range of materials, device components, and/or device configurations, the description is intended to include specific reference of each combination and/or variation corresponding to the disclosed range.
Every formulation or combination of components described or exemplified herein can be used to practice the invention, unless otherwise stated.
Whenever a range is given in the specification, for example, a density range, a number range, a temperature range, a time range, or a composition or concentration range, all intermediate ranges and subranges, as well as all individual values included in the ranges given are intended to be included in the disclosure. It will be understood that any subranges or individual values in a range or subrange that are included in the description herein can be excluded from the claims herein.
All patents and publications mentioned in the specification are indicative of the levels of skill of those skilled in the art to which the invention pertains. References cited herein are incorporated by reference herein in their entirety to indicate the state of the art as of their publication or filing date and it is intended that this information can be employed herein, if needed, to exclude specific embodiments that are in the prior art. For example, when composition of matter are claimed, it should be understood that compounds known and available in the art prior to Applicant's invention, including compounds for which an enabling disclosure is provided in the references cited herein, are not intended to be included in the composition of matter claims herein.
As used herein, “comprising” is synonymous with “including,” “containing,” or “characterized by,” and is inclusive or open-ended and does not exclude additional, unrecited elements or method steps. As used herein, “consisting of” excludes any element, step, or ingredient not specified in the claim element. As used herein, “consisting essentially of” does not exclude materials or steps that do not materially affect the basic and novel characteristics of the claim. In each instance herein any of the terms “comprising”, “consisting essentially of” and “consisting of” may be replaced with either of the other two terms. The invention illustratively described herein suitably may be practiced in the absence of any element or elements, limitation or limitations which is not specifically disclosed herein.
All art-known functional equivalents, of any such materials and methods are intended to be included in this invention. The terms and expressions which have been employed are used as terms of description and not of limitation, and there is no intention that in the use of such terms and expressions of excluding any equivalents of the features shown and described or portions thereof, but it is recognized that various modifications are possible within the scope of the invention claimed. Thus, it should be understood that although the present invention has been specifically disclosed by preferred embodiments and optional features, modification and variation of the concepts herein disclosed may be resorted to by those skilled in the art, and that such modifications and variations are considered to be within the scope of this invention as defined by the appended claims.
This application claims priority from U.S. Provisional Patent Application No. 63/138,842, filed on Jan. 19, 2021, the contents of which are incorporated herein by reference in their entirety.
This invention was made with government support under Contract No. DE-AC36-08GO28308 awarded by the Department of Energy. The government has certain rights in the invention.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/US22/12932 | 1/19/2022 | WO |
| Number | Date | Country | |
|---|---|---|---|
| 63138842 | Jan 2021 | US |
