Patent Publication Number: US-9905420-B2

Title: Methods of forming silicon germanium tin films and structures and devices including the films

Description:
FIELD OF INVENTION 
     The present disclosure generally relates to techniques for forming layers including silicon germanium tin and to structures and devices including such layers. More particularly, various embodiments of the disclosure relate to methods of forming silicon germanium tin layers using germane and/or silane, to methods of forming structures and devices including such layers, to systems for forming the layers and structures, and to structures and devices including the layers. 
     BACKGROUND OF THE DISCLOSURE 
     Various electronic devices, such as semiconductor devices, and photonic devices, such as lasers and solar devices, include or may desirably include silicon germanium tin (Si x Ge 1-x Sn y ) layers. For example, Si x Ge 1-x Sn y  layers can be used to form direct band gap devices, quantum well structures, and/or may be used to provide strain in, for example, an adjacent germanium layer to increase carrier mobility in the germanium layer. Si x Ge 1-x Sn y  layers can also be used to form tunable band gap devices as well as optical devices having tunable optical properties. To obtain the desired device properties, the Si x Ge 1-x Sn y  layers generally have a crystalline structure, which generally follows the crystalline structure of an underlying layer, such as a buffer layer. 
     Si x Ge 1-x Sn y  layers can be deposited or grown using a variety of techniques. For example, vacuum processes, including molecular beam epitaxy and ultra-high vacuum chemical vapor deposition, have been used to form Si x Ge 1-x Sn y  films. Unfortunately, such techniques are slow, expensive, and thus generally not well suited for high-volume manufacturing. 
     The germanium precursor for such processes typically includes digermane (Ge 2 H 6 ) or trigermane (Ge 3 H 8 ). When the film includes silicon, the silicon precursor typically includes a disilane (Si 2 H 6 ), trisilane (Si 3 H 8 ), or other higher order silane compounds, or hetero-nuclear Si—Ge compounds with the general formula of (H 3 Ge)xSiH 4-x  (x=1-4), (H 3 Si)xGeH 4-x  (x=1-4). 
     Although such processes generally work to deposit or grow crystalline Si x Ge 1-x Sn y  layers, use of digermane, trigermane, or higher order germane precursors and/or disilane or trisilane, is problematic in several respects. For example, formation of films or layers including Si x Ge 1-x Sn y  using digermane or higher order germane precursors, such as trigermane, is not selective when certain carrier gasses (e.g., hydrogen) and/or dopants (e.g., p-type dopants) are used with the precursor. Also, digermane is relatively unstable (explosive) in concentrated form; as a result, an amount of the precursor contained in a vessel may be limited, typically to less than 154 grams, which, in turn, causes throughput of processes using such a precursor to be relatively low. In addition, digermane and higher order germanes are relatively expensive. Similarly, higher order silanes are relatively expensive and can result in relatively slow growth rates. Accordingly, improved processes for forming Si x Ge 1-x Sn y  are desired. Further, improved methods suitable for high-volume manufacturing of structures and devices including a layer of Si x Ge 1-x Sn y  are desired. 
     SUMMARY OF THE DISCLOSURE 
     Various embodiments of the present disclosure relate to methods of forming Si x Ge 1-x Sn y  films, to structures and devices including Si x Ge 1-x Sn y  films, and to systems for forming the Si x Ge 1-x Sn y  films. The methods described herein can be used to form Si x Ge 1-x Sn y  films suitable for a variety of applications, including, for example, stressor films in semiconductor devices and tunable bandgap layers in photonic devices. While the ways in which various embodiments of the disclosure address the drawbacks of the prior art methods, films, structures, devices, and systems are discussed in more detail below, in general, the disclosure provides methods of forming Si x Ge 1-x Sn y  using silane and/or germane as precursors. Exemplary methods can be used to form films, structures, and/or devices including Si x Ge 1-x Sn y  in a cost efficient manner and/or can be used to form such films, structures and/or devices in a time efficient manner. Various methods described herein are particularly well suited for use in high volume manufacturing of structures and devices including Si x Ge 1-x Sn y  films. 
     As used herein, Si x Ge 1-x Sn y  films (also referred to herein as layers) are layers that can include the elements silicon, germanium, and tin. In accordance with various embodiments of the disclosure, the Si x Ge 1-x Sn y  films are crystalline and are epitaxially formed overlying a crystalline substrate or layer. The films can be in the form of an alloy. Exemplary Si x Ge 1-x Sn y  films include from 0 or greater than 0 at % to about 15 at % or about 2 at % to about 15 at % tin, from 0 or greater than 0 at % to about 30 at % or about 1 at % to about 30 at % silicon, or about 55 at % to about 65 at % or about 75 at % to about 95 at % germanium. The layers can include additional elements, such as carbon (e.g., GeSnSiC alloys) and/or other elements, such as phosphorous, boron, or other elements commonly used as dopants, and/or trace amount of other elements. 
     In accordance with some exemplary embodiments of the disclosure, methods of forming a Si x Ge Sn Y  layer on a substrate include the steps providing a reactor having a reaction space, providing a substrate within the reaction space, providing silane coupled to the reaction space, providing a germanium precursor (e.g., germane) coupled to the reaction space, providing a tin precursor source coupled to the reaction space, and epitaxially forming a layer of Si x Ge 1-x Sn y  on a surface of the substrate. One or more of the precursors can be mixed at or near an inlet of the reaction chamber—e.g., at an inlet or injection manifold of the reactor. In accordance with further aspects, a cross-flow reactor is used to form the Si x Ge 1-x Sn y  layer(s). In accordance with yet further aspects, a ratio of flowrate of silane to the tin precursor (not including carrier gasses) ranges from about 2 to about 5, or about 2 to about 10, or about 2 to about 15. Exemplary methods can further include providing additional precursors, such as carbon precursors and/or dopant precursors, to the reaction space; such additional precursor(s) can be mixed with one or more of the other precursors at or near the inlet of the reaction chamber and/or further upstream of the reactor. 
     Other exemplary methods of forming a Si x Ge 1-x Sn y  layer on a substrate include the steps providing a reactor (e.g., a cross-flow reactor) having a reaction space, providing a substrate within the reaction space, providing a silicon source (e.g., silane) coupled to the reaction space, providing germane coupled to the reaction space, providing a tin precursor source coupled to the reaction space, and epitaxially forming a layer of Si x Ge 1-x Sn y  on a surface of the substrate. A ratio of flowrate of silane to the tin precursor ranges from about 2 to about 15 or other silane:tin precursor ratios as set forth herein. Exemplary methods can further include providing additional precursors, such as carbon precursors and/or dopant precursors, to the reaction space; such additional precursor(s) can be mixed with one or more of the other precursors at or near the inlet or further upstream of the reaction chamber. 
     A reaction space temperature for methods described herein can range from about 200° C. to about 500° C., about 275° C. to about 475° C., or about 300° C. to about 420° C. Exemplary reaction chamber pressures during this step range from about 500 Torr to about 760 Torr, about 600 Torr to about 760 Torr, or about 700 Torr to about 760 Torr. The relatively low temperatures and/or relatively high pressures allow for low throughput times associated with manufacturing structures and devices comprising one or more Si x Ge 1-x Sn y  layers formed as described herein. 
     In accordance with exemplary aspects of various embodiments of the disclosure, a ratio of flowrates or partial pressures of the precursors can be selected to promote high-quality film formation under high volume manufacturing conditions. 
     In accordance with additional embodiments of the disclosure, a structure includes one or more Si x Ge 1-x Sn y  films—e.g., formed using a method disclosed herein. Structures can also include additional layers, such as layers typically used to form devices. For example, the structures can include a germanium layer, which can form a buffer layer, and/or a fin layer as part of a FinFET device. 
     In accordance with yet additional exemplary embodiments of the disclosure, a device includes or is formed using a structure including one or more Si x Ge 1-x Sn y  films. 
     And, in accordance with yet additional exemplary embodiments of the disclosure, a system for forming one or more Si x Ge 1-x Sn y  films includes a gas-phase reactor including a reaction space, a germanium precursor (e.g., germane) source coupled to the reaction chamber, a tin precursor source coupled to the reaction space, and a silicon precursor (e.g., silane) source coupled to the reaction space. The system can be configured to mix (e.g., have an operational control mechanism configured to cause mixing of) one or more of the precursors (e.g., all precursors) at or near an inlet of a reaction chamber (e.g., at an injection manifold). 
     Both the foregoing summary and the following detailed description are exemplary and explanatory only and are not restrictive of the present disclosure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING FIGURES 
       A more complete understanding of exemplary embodiments of the present disclosure may be derived by referring to the detailed description and claims when considered in connection with the following illustrative figures. 
         FIG. 1  illustrates a system for forming one or more Si x Ge 1-x Sn y  films in accordance with exemplary embodiments of the disclosure. 
         FIG. 2  illustrates a method of forming a Si x Ge 1-x Sn y  film in accordance with further exemplary embodiments of the disclosure. 
         FIG. 3  illustrates an XRD plot showing Si x Ge 1-x Sn y  layers of various compositions grown with fixed SiH 4 , GeH 4 , and SnCl 4  flows formed in accordance with exemplary embodiments of the disclosure. 
         FIG. 4  illustrates an RBS plot showing an exemplary Si x Ge 1-x Sn y  layer on Ge buffer with 5% Sn and 8% Si formed in accordance with exemplary embodiments of the disclosure. 
         FIG. 5  illustrates Raman spectra of various Si x Ge 1-x Sn y  films formed in accordance with exemplary embodiments of the disclosure. 
         FIGS. 6-13  illustrate exemplary structures according to yet additional exemplary embodiments of the present disclosure. 
     
    
    
     It will be appreciated that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of illustrated embodiments of the present disclosure. 
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS OF THE DISCLOSURE 
     The description of exemplary embodiments of methods, systems, structures, and devices provided below is merely exemplary and is intended for purposes of illustration only; the following description is not intended to limit the scope of the disclosure or the claims. Moreover, recitation of multiple embodiments having stated features is not intended to exclude other embodiments having additional features or other embodiments incorporating different combinations of the stated features. 
     The present disclosure relates, generally, to methods of forming layers, such as crystalline alloy layers including silicon, germanium, and tin, overlying a substrate. The silicon germanium tin (Si x Ge 1-x Sn y ) layers can include additional elements, such as carbon, which forms part of a crystalline lattice with the silicon germanium tin layer and/or dopants (e.g., p-type dopants, such as boron (B) and/or n-type dopants, such as phosphorous (P) and Arsenic (As)). 
     Exemplary Si x Ge 1-x Sn y  layers include from 0 or greater than 0 at % to about 15 at % tin, about 2 at % to about 15 at % tin, or about 3 at % to about 12 at % tin. Si x Ge 1-x Sn y  can include greater than 0 at % tin, greater than 2 at % tin, or greater than 3 at % tin. The Si x Ge 1-x Sn y  layers can additionally or alternatively include from 0 or greater than 0 at % to about 30 at % silicon, or about 1 at % to about 30 at % silicon, or about 3 at % to about 25 at % silicon. Exemplary Si x Ge 1-x Sn y  layers can additionally or alternatively include about 55 at % to about 65 at % germanium, or about 60 at % to about 70 at % germanium, or about 80 at % to about 90 at % germanium. When the layers include carbon, the Si x Ge 1-x Sn y C layers can include from 0 or greater than 0 at % to about 1 at % carbon, or about 2 at % to about 3 at % carbon, or about 4 at % to about 5 at % carbon. 
     The Si x Ge 1-x Sn y  layers can be used to form structures and devices suitable for a variety of applications, including strain layers to increase mobility of carriers in other layers in semiconductor devices, as part of quantum well structures and devices, and/or as layers in photonic devices. Exemplary structures and devices are discussed below. 
     As used herein, a “substrate” refers to any material having a surface onto which material can be deposited. A substrate can include a bulk material such as silicon (e.g., single crystal silicon, single crystal germanium, or other semiconductor wafer) or can include one or more layers overlying the bulk material. Further, the substrate can include various topologies, such as trenches, vias, lines, and the like formed within or on at least a portion of a layer of the substrate. Exemplary substrates include a silicon wafer, a layer comprising germanium overlying silicon, and a layer comprising germanium tin overlying silicon. 
     Turning now to the figures,  FIG. 1  illustrates a system  100  suitable for forming Si x Ge 1-x Sn y  layers on a substrate using the methods described herein. In the illustrated example, system  100  includes a reactor  102 , a silane source  104 , a germanium (e.g., germane) precursor  106  source, a tin precursor source  108 , purge and/or carrier gas source  110 , an optional mixer  112 , an optional intake plenum  114 , and an exhaust (e.g., vacuum) source  116 . Sources  104 - 110  may be coupled to mixer  112  or reactor  102  using lines  118 - 132  and valves  134 - 140 . Although not illustrated, a system, such as system  100 , may include additional sources and corresponding delivery lines for other precursors, such as carbon precursors and/or dopants (e.g., n-type dopants such as phosphorous or arsenic or p-type dopants such as boron). Additionally or alternatively, one or more dopants may be included in one or more of the precursor sources  102 - 108 . Further, although separately illustrated, two or more dopants may be mixed in a common source. 
     The sources can be relatively pure—e.g., about 99.999% or greater pure or can be mixed with a carrier. In the case of silane, silane source  104  can include about 1 to 10 at % silane in a carrier or about 100 at % silane. Similarly, the germanium precursor source  106  (e.g., germane) can include about 1.5% to about 5 at % or about 10 at % germane in a carrier. Further, exemplary systems can comprise, consist essentially of, or consist of the precursors noted herein. 
     Reactor  102  can be a standalone reactor or part of a cluster tool. Further, reactor  102  can be dedicated to a particular process, such as a deposition process, or reactor  102  may be used for other processes—e.g., for layer passivation, cleaning, and/or etch processing. For example, reactor  102  can include a reactor typically used for epitaxial chemical vapor deposition (CVD) processing, such as an Epsilon® 2000 Plus, Epsilon® 3200, or Intrepid XP, available from ASM, and may include direct plasma, and/or remote plasma apparatus (not illustrated) and/or various heating systems, such as radiant, inductive, and/or resistive heating systems (also not illustrated). Using a plasma may enhance the reactivity of one or more precursors. The illustrated reactor is a single-substrate, horizontal-flow (cross-flow) reactor, which enables laminar flow of reactants over a substrate  142 , with low residence times, which, in turn, facilitates relatively rapid sequential substrate processing. An exemplary CVD reactor suitable for system  100  is described in U.S. Pat. No. 7,476,627, issued to Pomarede et al. on Jan. 13, 2009, the contents of which are hereby incorporated herein by reference, to the extent such contents do not conflict with the present disclosure. The cross-flow reactor was found to produce high-quality Si x Ge 1-x Sn y  layers on a surface of a substrate under conditions that are suitable for high-volume, relatively low-cost manufacturing. 
     An operating pressure of a reaction chamber  144  of reactor  102  may vary in accordance with various factors. Reactor  102  may be configured to operate at near atmospheric pressure or at lower pressures, which allows relatively fast formation of the Si x Ge 1-x Sn y  layers—e.g., compared to ultra-high vacuum or molecular beam epitaxy techniques. By way of examples, an operating pressure of reactor  102  during layer formation steps ranges from about 500 Torr to about 760 Torr, about 600 Torr to about 760 Torr, or about 700 Torr to about 760 Torr. A reaction space temperature can range from about 200° C. to about 500° C., about 275° C. to about 475° C., or about 300° C. to about 420° C. 
     Silane source  104  includes silane (SiH 4 ) and can optionally include a carrier. Silane source  104  can optionally include one or more dopant compounds, such as compounds typically used to fabricate photonic and/or semiconductor devices. Exemplary p-type dopant compounds include B 2 H 6  and exemplary n-type dopant compounds include PH 3  and AsH 3 . Use of silane is advantageous over the use of higher order silane compounds, such as disilane, trisilane, tetrasilane (Si 4 H 10 ), neopentasilane (Si 5 H 12 ), and higher order silanes, because silane is relatively less expensive and is more readily available. The inventors found that using pressures, a cross-flow reactor, and/or the ratio of reactants disclosed herein allows for formation of high-quality Si x Ge 1-x Sn y  layers using silane—rather than higher order silanes. 
     Germanium precursor source  106  can include germane (GeH 4 ) and may optionally include one or more carrier gasses and/or dopant compounds, such as compounds typically used to fabricate photonic and/or semiconductor devices—e.g., B 2 H 6  and/or PH 3 , AsH 3 . 
     Use of germane is advantageous over other precursors, such as digermane, trigermane, and other higher-order germanes, used to form Si x Ge 1-x Sn y  layers, because germane is relatively selective when mixed with various carrier gasses (e.g., hydrogen, nitrogen, or the like) and is also relatively selective, even when dopants (e.g., p-type dopants) are used with the precursor. Also, germane is relatively safe, compared to higher order digermanes, and thus can be used and/or transported in higher quantities, compared to higher order germanes. Also, germane can be used as a precursor for other layers, such as germanium, and is more readily available and is less expensive, compared to higher-order germane compounds. 
     Tin precursor source  108  includes any compound suitable for providing tin to a Si x Ge 1-x Sn y  layer. Exemplary tin precursors include tin chloride (SnCl 4 ), deuterated stannane (SnD 4 ), and methyl and/or halide substituted stannanes, such as compounds having a formula Sn(CH 3 ) 4-n X n , in which X is H, D (deuterium), Cl, or Br and n is 0, 1, 2, or 3; ZSn(CH 3 ) 3-n X n , in which Z is H or D, X is Cl or Br, and n is 0, 1, or 2; Z2Sn(CH 3 ) 2-n X n  in which Z is H or D, X is Cl or Br, and n is 0 or 1; or SnBr 4 . Some exemplary tin precursors suitable for use with the present disclosure are discussed in more detail in application Ser. No. 13/783,762, filed Mar. 4, 2013, entitled TIN PRECURSORS FOR VAPOR DEPOSITION AND DEPOSITION PROCESSES, the contents of which are hereby incorporated herein by reference, to the extent such contents do not conflict with the present disclosure. 
     Purge and/or carrier gas source  110  may include any suitable purge or carrier gas. Exemplary gasses suitable as carrier and purge gasses include nitrogen, argon, helium, and hydrogen. 
     System  100  can also include a gas distribution system. An exemplary gas distribution system, which allows for fast switching between gasses (e.g., from sources  104 - 110 ) is set forth in U.S. Pat. No. 8,152,922 to Schmidt et al., issued Apr. 10, 2012, entitled “Gas Mixer and Manifold Assembly for ALD Reactor,” the contents of which are hereby incorporated herein by reference, to the extent the contents do not conflict with the present disclosure. The gas distribution system may be used to, for example, mix one or more precursor gasses and a carrier gas (which may be the same or different from a purge gas from gas source  108 ) prior to the gasses reaching plenum  114  or reactor  102 . 
     Turning now to  FIG. 2 , an exemplary method  200  of forming a Si x Ge 1-x Sn y  layer is illustrated. Method  200  includes the steps of providing a gas-phase reactor (step  202 ), providing a substrate within the gas-phase reactor (step  204 ), providing precursors to a reaction space of the reactor (step  206 ), and forming a Si x Ge 1-x Sn y  layer overlying the substrate (step  208 ). Method  200  can optionally include one or more of forming an insulating layer overlying the substrate (step  210 ), and/or forming a via within the insulating layer (step  212 ). 
     During step  202 , a gas-phase reactor, such as a CVD reactor suitable for epitaxial growth, is provided. The reactor can be a single-substrate, laminar cross-flow reactor. Suitable reactors are available from ASM, under the name Epsilon® 2000 Plus, Epsilon® 3200, and Intrepid XP. 
     During step  204 , a substrate is provided within a reaction chamber of a reactor. The substrate may be received from a loading load lock of a reactor system and transported to the reaction space, such as a reaction chamber, using a suitable transfer mechanism. During this step, the reaction space can be brought to a suitable pressure and temperature for Si x Ge 1-x Sn y  layer formation, such as the pressures and temperatures noted herein. 
     At step  206 , the silane, germanium precursor, and the tin precursor are provided to the reaction space of the reactor. The precursors can comprise, consist essentially of, or consist of these precursors. The silane, germanium precursor, and tin precursor can be mixed (e.g., at mixer  112 ) prior to entering the chamber. The silane, germanium precursor, and tin precursor can individually or in various combinations be mixed with one or more carrier gasses prior to entering the reaction space. One or more of the precursors, in any combination, can be mixed with a carrier upstream of the reaction chamber, such as at a mixer, upstream of a mixer, and/or within the respective source. During this step, a partial pressure of silane can range from about 5 Torr to about 20 Torr; a partial pressure of the germanium precursor (e.g., germane) can range from about 300 Torr to about 450 Torr; or a partial pressure of the tin precursor (e.g., tin chloride) can range from about 1 Torr to about 3 Torr. 
     During step  208 , a crystalline layer (e.g., an epitaxial layer) of Si x Ge 1-x Sn y  is formed overlying a substrate. As noted above, an operating pressure of a reaction space during layer formation steps can range from about 500 Torr to about 760 Torr, about 600 Torr to about 760 Torr, or about 700 Torr to about 760 Torr. And, a reaction space temperature can range from about 200° C. to about 500° C., about 275° C. to about 475° C., or about 300° C. to about 420° C. 
     During step  210 , any suitable insulating layer, such as silicon oxide or silicon nitride, is deposited onto the substrate. Then, during step  212 , one or more vias are formed within the insulating layer. Reactive ion etching or other suitable technique can be used to form the one or more vias. 
     In the cases where steps  210  and  212  are performed, the Si x Ge 1-x Sn y  layer formed during step  206  can be selectively formed within the vias. As noted above, use of a germane precursor is advantageous because it is relatively selective when using a variety of carrier gasses, such as hydrogen, and/or when the layer includes one or more dopants, such as p-type dopants. 
       FIG. 3  illustrates an X-Ray diffraction (XRD) plot of Si x Ge 1-x Sn y  layers of various compositions grown with fixed silane, germane, and tin chloride flow rates over a layer of germanium overlying a silicon substrate. A reaction space temperature during the deposition of the films varied between 300° C. and 375° C. The plot illustrates that a composition of the Si x Ge 1-x Sn y  layers can be adjusted to be lattice matched to germanium or can be increasingly strained. 
       FIG. 4  illustrates aligned and random yield of Rutherford backscattering spectra of a Si x Ge 1-x Sn y  layer formed overlying a germanium layer on a silicon substrate. The Si x Ge 1-x Sn y  includes about 5% tin and about 8% silicon and was grown at a temperature of about 320° C. The low yield of the aligned spectra relative to the random spectra indicates that the Si x Ge 1-x Sn y  layer is a substitutional alloy. 
       FIG. 5  illustrates Raman spectra of Si x Ge 1-x Sn y  layers of various compositions, illustrating ternary binding in the films and that the films are substitutional alloys. 
       FIGS. 6-12  illustrate exemplary structures  600 - 1200  that can be formed—e.g., using the exemplary systems and/or methods described herein. 
     Structure  600  includes a substrate  602 , a buffer layer  604 , and a Si x Ge 1-x Sn y  layer  606  (e.g., epitaxially formed overlying layer  604 ). Substrate  602  can include, for example, a silicon substrate. Substrate  602  can include additional layers of materials used to form electronic or photonic devices. Buffer layer  604  can include or be, for example, a layer of germanium that is epitaxially formed overlying substrate  602 . Si x Ge 1-x Sn y  layer  606  can be formed using, for example, method  200 . Structure  600  can be used to form a variety of electronic or photonic devices. 
     A thickness of buffer layer  604  can range from, for example, about 0.5 to about 0.7, or about 0.8 to about 0.9, or be about one micron thick. A thickness of Si x Ge 1-x Sn y  layer  606  can range from about 1 to about 9, or about 10 nm to about 100 nm in thickness. 
     Structure  700  is similar to structure  600 , except structure  700  includes an additional layer  708 . Structure  700  includes a substrate  702 , a buffer layer  704 , a Si x Ge 1-x Sn y  layer  706 , and a germanium layer  708 . Substrate  702 , buffer layer  704 , and Si x Ge 1-x Sn y  layer  706  can be the same as the corresponding substrate and layers described in connection with  FIG. 6  and can have the same thicknesses. A thickness of germanium layer  708  can range from about 1 to about 3, or about 4 to about 9 or be about 10 nm thick. Germanium layer  708  can be epitaxially formed overlying Si x Ge 1-x Sn y  layer  706  using, e.g., an epitaxial process with germane as a precursor. 
     Structure  800  includes a substrate  802 , a buffer layer  804 , a Si x Ge 1-x Sn y  layer  806 , and a germanium tin (GeSn) layer  808  epitaxially formed overlying Si x Ge 1-x Sn y  layer  806 . Substrate  802  and layers  804 - 806  can be the same or similar to corresponding layers described above in connection with  FIGS. 6 and 7  and have the same thicknesses. GeSn layer  808  can have a thickness of about 1 to about 3, or about 4 to about 9, or be about 10 nm. GeSn layer  808  can be formed by, for example, using germane and a tin precursor such as tin chloride. GeSn layer  808  can include, for example, about 1 at % to about 8 at % or about 9 at % to about 15 at % tin. 
     Structure  900  includes a substrate  902 , a germanium layer  904 , a GeSn layer  906 , and a Si x Ge 1-x Sn y  layer  908 . The composition of the layers can be the same as the corresponding layers described above in connection with  FIG. 8  (with germanium layer  904  corresponding to buffer layer  804 ). In the illustrated example, buffer layer  904  can have the same thickness as buffer layers  604 - 804 ; a thickness of GeSn layer can range from about 100 nm to about 400 nm, or about 500 nm to about 900 nm, or be about 1000 nm. Si x Ge 1-x Sn y  layer  908  can have the same thickness as Si x Ge 1-x Sn y  layers  606 ,  706 , and  806 . Structure  900  is similar to structure  800 , except GeSn layer  906  and Si x Ge 1-x Sn y  layer  908  are formed in reverse order—compared to the structure illustrated in  FIG. 8 . 
     Structure  1000 , which is suitable for quantum well structures and devices, includes a substrate  1002 , a buffer layer  1004 , first Si x Ge 1-x Sn y  layer  1006 , GeSn layer  1008 , and second Si x Ge 1-x Sn y  layer  1006 . The various layers can be formed as described above. Buffer layer  1004 , first and second Si x Ge 1-x Sn y  layers  1006  and  1010 , and GeSn layer  1008  can have the same thickness noted above. By way of example, buffer layer  1004  can be about 1 micron thick, first Si x Ge 1-x Sn y  layer  1006  and second Si x Ge 1-x Sn y  layer  1010  can each be about 50 nm thick, and GeSn layer  1008  can be about 10 nm thick. Layers  1008 - 1010  can be repeated a desired number of times to form a quantum well structure. 
       FIG. 11  illustrates another structure  1100  that is suitable for use as a quantum well structure or device. Structure  1100  includes a substrate  1102 , a buffer layer  1104 , a first Si x Ge 1-x Sn y  layer  1106 , a first Ge layer  1108 , a GeSn layer  1110 , a second Ge layer  1112 , and a second Si x Ge 1-x Sn y  layer  1114 . Buffer layer  1104 , first and second Si x Ge 1-x Sn y  layers  1106  and  1114 , first and second Ge layers  1108  and  1112 , and GeSn layer  1110  can have the same thickness noted above. By way of example, buffer layer  1104  can be about 1 micron thick, first Si x Ge 1-x Sn y  layer  1106  can be about 50 nm thick, first Ge layer  1108  and second Ge layer  1112  can be about 50 nm thick, GeSn layer  1110  can be about 10 nm thick, and second Si x Ge 1-x Sn y  layer  1114  can be about 10 nm thick. Layers  1106 - 1114  can be repeated a desired number of times to form a quantum well structure. 
       FIG. 12  illustrates yet another structure  1200  in accordance with various embodiments of the disclosure. Structure  1200  includes substrate  1202 , first Si x Ge 1-x Sn y  layer  1204 , GeSn layer  1206 , and second Si x Ge 1-x Sn y  layer  1208 . Structure  1200  is similar to structure  1000 , except structure  1200  does not include buffer layer  1004 . The layers of structure  1200  can be formed using the same techniques used to form structure  1000  and the layers can have the same or similar thicknesses. 
       FIG. 13  illustrates yet another structure  1300  in accordance with additional exemplary embodiments of the disclosure. Structure  1300  includes a substrate  1302 , an insulating layer  1304 , a via  1306  formed within insulating layer  1304 , a germanium layer  1308  (e.g., epitaxially formed overlying substrate  1302 ), and a Si x Ge 1-x Sn y  layer  1310  (e.g., epitaxially formed overlying layer  1308 ). Layers  1308  and/or  1310  can be selectively formed within via  1306 —e.g., using method  200 . Substrate  1302 , germanium layer  1308 , and Si x Ge 1-x Sn y  layer  1310  can be the same or similar to respective layers described above and can have the same or similar thicknesses. Insulating layer  1304  can include silicon oxide, silicon nitride, and/or silicon oxynitride. A thickness of insulating layer  1304  can range from about 1 to about 10 nm, or about 10 to about 100 nm. 
     It is to be understood that the configurations and/or approaches described herein are exemplary in nature, and that these specific embodiments or examples are not to be considered in a limiting sense. In the case of exemplary methods, specific routines or steps described herein can represent one or more of any number of processing strategies. Thus, the various acts illustrated can be performed in the sequence illustrated, performed in other sequences, performed simultaneously, or omitted in some cases. 
     The subject matter of the present disclosure includes all novel and nonobvious combinations and subcombinations of the various processes, layers, systems and configurations, and other features, functions, acts, and/or properties disclosed herein, as well as any and all equivalents thereof.