{ "spore": "profile", "id": "silicon-germanium", "spore_version": "0.2", "family": "semiconductor-materials", "name": "Silicon-germanium alloy", "abbreviation": "SiGe", "role": "semiconductor", "category": "semiconductors", "type": "silicon", "summary": "SiGe is an alloy of silicon and germanium, written Si1-xGex, and it can be made in any ratio of the two (Wikipedia). NASA radioisotope generators on Voyager 1 and 2, Galileo, Ulysses, Cassini and New Horizons used SiGe thermoelectric couples. NASA calls SiGe a popular RTG choice because it is mechanically robust and stable in air or vacuum at high temperature. In a 2023 paper, p-type Si80Ge20B2 reached a figure of merit (zT) of 0.75 at 1000 K, and 0.8 with a MnTe addition. SiGe is also used in heterojunction bipolar transistors (HBTs), and IHP reports a SiGe HBT with fT/fmax of 505 GHz/720 GHz.", "best_for": "High-temperature thermoelectric legs for radioisotope generators, and SiGe transistors for fast RF chips", "weakest_at": "Thermoelectric efficiency: NASA says the figure of merit of Si-Ge is much lower than that of lead telluride", "identity": { "formula": "Si1-xGex, a silicon-germanium alloy in any ratio; the thermoelectric composition in the sources read is Si80Ge20", "designations": [], "source": "wiki-sige", "where": "Lead section, composition sentence (an alloy of silicon and germanium in any molar ratio)" }, "tags": { "environments": [], "stresses": [], "applications": [ "electronics-and-chips", "batteries" ] }, "properties": [ { "benchmark": "figure_of_merit_zt", "label": "Thermoelectric figure of merit, p-type Si80Ge20B2", "value": 0.75, "bound": "exact", "unit": "-", "scope": "material", "conditions": { "composition": "Si80Ge20B2, pristine, p-type", "temperature": "1000 K" }, "method": "Value printed in the paper abstract", "status": "ground", "source": "ivanova2023", "where": "Abstract, zT values", "source_detail": { "title": "Ivanova et al., p-type SiGe-based composite produced by mechanical alloying and spark plasma sintering, Materials Letters 357 (2023), 135746", "url": "https://mdr.nims.go.jp/datasets/8ac554e7-8275-4a96-90f5-99a2ea57ef18", "kind": "paper", "license": "In Copyright (repository record); values cited, not reproduced" } }, { "benchmark": "figure_of_merit_zt", "label": "Thermoelectric figure of merit, Si80Ge20B2 with 4 wt% MnTe", "value": 0.8, "bound": "exact", "unit": "-", "scope": "material", "conditions": { "composition": "Si80Ge20B2 plus 4 wt% MnTe, p-type", "temperature": "1000 K" }, "method": "Value printed in the paper abstract", "status": "ground", "source": "ivanova2023", "where": "Abstract, zT values", "source_detail": { "title": "Ivanova et al., p-type SiGe-based composite produced by mechanical alloying and spark plasma sintering, Materials Letters 357 (2023), 135746", "url": "https://mdr.nims.go.jp/datasets/8ac554e7-8275-4a96-90f5-99a2ea57ef18", "kind": "paper", "license": "In Copyright (repository record); values cited, not reproduced" } }, { "benchmark": "figure_of_merit_zt", "label": "Thermoelectric figure of merit, p-type SiGe (up to)", "value": 0.7, "bound": "exact", "unit": "-", "scope": "material", "conditions": { "temperature": "1000 °C", "bound": "up to, as printed" }, "method": "Value printed on a reference page (Wikipedia); zT is dimensionless and no unit is printed", "status": "ground", "source": "wiki-sige", "where": "Thermoelectric application section, p-SiGe bullet", "source_detail": { "title": "Wikipedia, Silicon-germanium (composition, uses, thermoelectric and RTG sections)", "url": "https://en.wikipedia.org/wiki/Silicon%E2%80%93germanium", "kind": "web", "license": "page content, cited as published" } }, { "benchmark": "figure_of_merit_zt", "label": "Thermoelectric figure of merit, n-type SiGe (up to)", "value": 1, "bound": "exact", "unit": "-", "scope": "material", "conditions": { "temperature": "1000 °C", "bound": "up to, as printed" }, "method": "Value printed on a reference page (Wikipedia); zT is dimensionless and no unit is printed", "status": "ground", "source": "wiki-sige", "where": "Thermoelectric application section, n-SiGe bullet", "source_detail": { "title": "Wikipedia, Silicon-germanium (composition, uses, thermoelectric and RTG sections)", "url": "https://en.wikipedia.org/wiki/Silicon%E2%80%93germanium", "kind": "web", "license": "page content, cited as published" } }, { "benchmark": "seebeck_coefficient", "label": "Seebeck coefficient, p-type Si80Ge20B2 (first value in abstract)", "value": 252, "bound": "exact", "unit": "uV/K", "scope": "material", "conditions": { "composition": "Si80Ge20B2, pristine, p-type", "temperature": "1000 K" }, "method": "Value printed in the paper abstract; the abstract reads it as a fall from 252 to 197 when MnTe is added", "status": "ground", "source": "ivanova2023", "where": "Abstract, Seebeck coefficient sentence", "source_detail": { "title": "Ivanova et al., p-type SiGe-based composite produced by mechanical alloying and spark plasma sintering, Materials Letters 357 (2023), 135746", "url": "https://mdr.nims.go.jp/datasets/8ac554e7-8275-4a96-90f5-99a2ea57ef18", "kind": "paper", "license": "In Copyright (repository record); values cited, not reproduced" } }, { "benchmark": "seebeck_coefficient", "label": "Seebeck coefficient, p-type Si80Ge20B2 with 4 wt% MnTe (second value in abstract)", "value": 197, "bound": "exact", "unit": "uV/K", "scope": "material", "conditions": { "composition": "Si80Ge20B2 plus 4 wt% MnTe, p-type", "temperature": "1000 K" }, "method": "Value printed in the paper abstract", "status": "ground", "source": "ivanova2023", "where": "Abstract, Seebeck coefficient sentence", "source_detail": { "title": "Ivanova et al., p-type SiGe-based composite produced by mechanical alloying and spark plasma sintering, Materials Letters 357 (2023), 135746", "url": "https://mdr.nims.go.jp/datasets/8ac554e7-8275-4a96-90f5-99a2ea57ef18", "kind": "paper", "license": "In Copyright (repository record); values cited, not reproduced" } }, { "benchmark": "hot_junction_temperature", "label": "Hot-junction temperature, SiGe stage of a 1968 generator study", "value": 1089, "value_high": 1255, "bound": "range", "unit": "K", "scope": "material", "conditions": { "basis": "design hot-junction temperatures in a parametric study, not measured material limits" }, "method": "Values stated in a NASA Lewis parametric analysis (the study gives 811 K for lead telluride)", "status": "ground", "note": "Design temperatures for a generator model. The property name hot_junction_temperature is not in the canonical list (see gaps).", "source": "nasa-tmx1453", "where": "Summary, sentence on hot-junction temperatures for lead telluride and Si-Ge", "source_detail": { "title": "Parametric analysis of radioisotope-thermoelectric generators, NASA Lewis TM X-1453 (1968)", "url": "https://ntrs.nasa.gov/citations/19680005161", "kind": "report", "license": "public domain (NASA)" } }, { "benchmark": "hot_junction_temperature", "label": "Hot-junction temperature, MHW-RTG SiGe couples", "value": 1273, "bound": "exact", "unit": "K", "scope": "material", "conditions": { "device": "MHW-RTG, Voyager era", "couples": "312 SiGe thermoelectric couples" }, "method": "Value printed on a reference page (Wikipedia)", "status": "ground", "source": "wiki-rtg-app", "where": "MHW-RTG section, SiGe couples paragraph", "source_detail": { "title": "Wikipedia, Application of silicon-germanium thermoelectrics in space exploration", "url": "https://en.wikipedia.org/wiki/Application_of_silicon-germanium_thermoelectrics_in_space_exploration", "kind": "web", "license": "page content, cited as published" } }, { "benchmark": "cold_junction_temperature", "label": "Cold-junction temperature, MHW-RTG SiGe couples", "value": 573, "bound": "exact", "unit": "K", "scope": "material", "conditions": { "device": "MHW-RTG, Voyager era", "couples": "312 SiGe thermoelectric couples" }, "method": "Value printed on a reference page (Wikipedia)", "status": "ground", "source": "wiki-rtg-app", "where": "MHW-RTG section, SiGe couples paragraph", "source_detail": { "title": "Wikipedia, Application of silicon-germanium thermoelectrics in space exploration", "url": "https://en.wikipedia.org/wiki/Application_of_silicon-germanium_thermoelectrics_in_space_exploration", "kind": "web", "license": "page content, cited as published" } }, { "benchmark": "density", "label": "Density assumed for Si-Ge elements in a generator weight model", "value": 4.31, "bound": "exact", "unit": "g/cm3", "scope": "material", "conditions": { "basis": "input to a 1968 weight model, not a measurement", "composition": "not stated" }, "method": "Value stated in a NASA Lewis analysis", "status": "ground", "note": "The study used this value for weight only. The Ioffe density fit for Si1-xGex gives a lower value at x = 0.2 (about 3.0 g/cm3 by arithmetic), so do not treat 4.31 as a measured density.", "source": "nasa-tmx1501", "where": "Weight analysis paragraph, sentence on the Si-Ge element density", "source_detail": { "title": "Ward and Ruch, Parametric analysis of radioisotope cascaded thermoelectric generators, NASA TM X-1501 (1968)", "url": "https://ntrs.nasa.gov/citations/19680005116", "kind": "report", "license": "public domain (NASA)" } } ], "corrosion": [ { "environment": "Air or vacuum at high temperature (RTG operation)", "headline": "NASA says SiGe is stable in air or vacuum at high temperature.", "effect": "The NASA report lists SiGe as a popular RTG choice for high temperature, mechanically robust, stable in air or vacuum, with reasonable ZT. No oxidation rate, mass change or temperature limit is given.", "rating": "low", "conditions": { "basis": "qualitative statement in the source; no rate or temperature number printed" }, "source": "nasa-wsi2", "where": "Silicon Germanium Alloys slide, Popular choice for RTG systems bullet" }, { "environment": "Dry oxygen at 850 to 1000 °C (thermal oxidation of Si1-xGex, x = 0.13)", "headline": "Ge atoms are pushed out of the oxide at the interface and do not enter the oxide layer.", "effect": "The Osaka study of a fully strained Si0.87Ge0.13 layer on Si oxidized in dry O2 at 850 to 1000 °C. Ordered SiO2 formed, and the authors describe the characteristic of SiGe oxidation as the ejection of Ge atoms from the interface between the surface oxide and the SiGe layer, without their incorporation into the oxide layer.", "rating": "unknown", "conditions": { "x": 0.13, "oxidant": "dry O2", "temperature": "850 to 1000 °C" }, "source": "osaka-prb2010", "where": "Introduction and oxidation results, paragraph on Ge ejection from the interface" }, { "environment": "Wet and dry oxidation at high temperature", "headline": "Wet oxidation of SiGe is faster than for Si, while dry oxidation is about equal or slightly faster.", "effect": "The Osaka paper's introduction says that SiGe oxidation is faster than that of Si under wet oxidation conditions, but almost equal or slightly higher under dry oxidation. No rate constants are given in the text read.", "rating": "unknown", "conditions": { "basis": "literature summary in the introduction of the Osaka paper; no rate number read" }, "source": "osaka-prb2010", "where": "Introduction, paragraph comparing wet and dry oxidation" } ], "risks": { "hazards": [ { "text": "The only SDS read for this profile is for germanium (Pure Tech, revised 10/89). It says germanium is considered to be of low toxicity and may be a mild skin irritant. Inhalation effects are listed as unknown. No SDS for a SiGe alloy was read for this profile.", "ghs": [], "source": "ge-msds", "where": "Section 4, Health hazard data" } ], "failure_risks": [ { "mode": "Grain growth in nanostructured SiGe", "trigger": "Long operation at high temperature", "consequence": "NASA says thermally induced grain growth can hinder the practical use of nano-sized SiGe grains, because the ZT gain from small grains is lost as the grains grow.", "severity": "moderate", "source": "nasa-wsi2", "where": "Enhancing Si/Ge slide, last bullet" }, { "mode": "Germanium supply interruption", "trigger": "China's ban on germanium exports to the United States in 2024", "consequence": "USGS reports that US imports of germanium metal fell 67 percent in 2025 to an estimated 7,000 kg, and that net import reliance was above 50 percent in every year from 2021 to 2025e. Germanium is about 20 percent of a Si80Ge20 alloy, so germanium supply sets the cost and availability of the alloy, while silicon is far more abundant.", "severity": "moderate", "source": "usgs-ge-2026", "where": "Events, Trends, and Issues; Salient Statistics, net import reliance row" } ], "side_effects": [], "handling": [ { "text": "The germanium SDS lists germanium as a material that fractures mechanically, so SiGe wafers and ingots should be handled as brittle solids.", "source": "ge-msds", "where": "Protection section, MECHANICAL (General) line" }, { "text": "The germanium SDS lists incompatibilities with bromine, chlorine, fluorine, oxygen and potassium chlorate when germanium is heated.", "source": "ge-msds", "where": "Section 6, Reactivity data, incompatibility line" } ], "mitigations": [] }, "uses": [ { "application": "electronics-and-chips", "device": "SiGe heterojunction bipolar transistors (HBTs) in RF and mixed-signal chips", "example": "IHP presented a SiGe HBT with fT/fmax of 505 GHz/720 GHz at the 2016 International Electron Devices Meeting (IEDM).", "source": "ihp-2016", "where": "Press release title and first paragraph" }, { "application": "electronics-and-chips", "device": "SiGe strain layer in CMOS transistors", "example": "Wikipedia says SiGe is used as a strain-inducing layer for CMOS transistors, and that HBTs allow CMOS logic to be integrated into mixed-signal circuits.", "source": "wiki-sige", "where": "Lead section, Uses paragraph" }, { "application": "batteries", "device": "Radioisotope thermoelectric generators (MHW-RTG and GPHS-RTG; a power source, not a battery)", "example": "MHW-RTG units with SiGe couples flew on Voyager 1 and 2 (launched 1977). GPHS-RTG units with the same SiGe technology flew on Galileo (October 18, 1989), Ulysses (October 6, 1990), Cassini (October 15, 1997) and New Horizons (January 19, 2006).", "source": "wiki-rtg-app", "where": "Application history, MHW-RTG and GPHS-RTG subsections" }, { "application": "batteries", "device": "SiGe thermoelectric legs in radioisotope generators (power source, not a battery)", "example": "NASA's report on SiGe with tungsten silicide calls SiGe a popular choice for RTG systems, citing its high temperature, mechanical robustness and stability in air or vacuum.", "source": "nasa-wsi2", "where": "Silicon Germanium Alloys slide, first bullet group" } ], "supply": [ { "subject": "Silicon (about 80 percent of a Si80Ge20 alloy)", "abundance": "The USGS silicon chapter gives no crustal abundance figure. It says world and domestic resources for making silicon metal are abundant.", "producers": [ { "country": "China", "share_percent": 80, "year": 2025 } ], "critical_lists": [ { "list": "USGS 2025 List of Critical Minerals (silicon added in 2025)", "listed": true } ], "recycling": "USGS silicon chapter: recycling is insignificant.", "substitutes": [ "USGS: gallium arsenide and germanium are the principal substitutes for silicon in semiconductor and infrared applications." ], "source": "usgs-si-2026", "where": "World Production table (silicon metal, 2024 and 2025 columns); Salient Statistics; Recycling; Substitutes; Final 2025 critical list paragraph" }, { "subject": "Germanium (about 20 percent of a Si80Ge20 alloy)", "abundance": "No abundance figure was read in the germanium chapter. It says resources are linked to zinc and lead-zinc-copper sulfide ores, and that reserves were not widely reported.", "producers": [], "critical_lists": [], "recycling": "USGS: much germanium removed in machining infrared optics is routinely recycled as new scrap, and germanium wafers used as solar-cell substrates are recycled. The USGS says the information available was inadequate for reliable estimates of secondary germanium.", "substitutes": [ "USGS: silicon or gallium arsenide substitute for germanium in certain electronic applications." ], "source": "usgs-ge-2026", "where": "Salient Statistics; Import Sources (2021 to 2024); Recycling; Substitutes" } ], "media": [], "documents": [ { "title": "Ivanova et al., p-type SiGe-based composite produced by mechanical alloying and spark plasma sintering, Materials Letters 357 (2023), 135746 (NIMS repository record)", "type": "paper", "url": "https://mdr.nims.go.jp/datasets/8ac554e7-8275-4a96-90f5-99a2ea57ef18", "year": 2023 }, { "title": "Mackey, Sehirlioglu and Dynys, WSi2 in Si1-xGex composites: processing and thermoelectric properties (NASA NTRS 20150002719)", "type": "report", "url": "https://ntrs.nasa.gov/citations/20150002719", "year": 2015 }, { "title": "Parametric analysis of radioisotope-thermoelectric generators, NASA Lewis TM X-1453 (1968)", "type": "report", "url": "https://ntrs.nasa.gov/citations/19680005161", "year": 1968 }, { "title": "Ward and Ruch, Parametric analysis of radioisotope cascaded thermoelectric generators, NASA TM X-1501 (1968)", "type": "report", "url": "https://ntrs.nasa.gov/citations/19680005116", "year": 1968 }, { "title": "Shimura et al., Residual order in the thermal oxide of a fully strained SiGe alloy on Si, Physical Review B 81, 033308 (2010)", "type": "paper", "url": "https://hdl.handle.net/11094/85489", "year": 2010 }, { "title": "USGS Mineral Commodity Summaries 2026, Silicon", "type": "report", "url": "https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-silicon.pdf", "year": 2026 }, { "title": "USGS Mineral Commodity Summaries 2026, Germanium", "type": "report", "url": "https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-germanium.pdf", "year": 2026 }, { "title": "Pure Tech Material Safety Data Sheet, Germanium (last revision 10/89)", "type": "sds", "url": "https://cores.research.utdallas.edu/files/2023/04/germanium.pdf", "year": 1989 } ], "gaps": [ "Thermal conductivity of SiGe at a stated composition and temperature: not found in a page read for this profile. The Basu et al. 2014 RSC page returned 403, the AIP Advances 2019 record on DOAJ returned a bot check, and the Inorganics 2025 MDPI paper returned 403. The Materials Letters abstract gives no absolute thermal conductivity.", "Melting point of SiGe: the Ioffe page gives solidus Ts = 1412 - 738x + 263x2 degC and liquidus Tl = 1412 - 80x - 395x2 degC (Stohr and Klemm 1954). These are formulas, not values at a stated composition, so no value is given. The Ioffe page was read over plain HTTP because its HTTPS certificate failed.", "Density of SiGe at a stated composition: the Ioffe fit (2.329 + 3.493x - 0.499x2 g/cm3 at 300 K) was read but is a formula. The only density value given is the 1968 weight-model input of 4.31 g/cm3, which does not match the fit.", "Thermal-conductivity formula on the Ioffe page (0.046 + 0.084x W/cm/K) gives values that do not match the pure-Si and pure-Ge entries printed on the same page (1.3 and 0.58 W/cm/K), so it was not used.", "Band gap, electron and hole mobility, lattice constant, dielectric constant and elastic constants of SiGe at a stated composition: not read as printed values in this run. Wikipedia gives only the qualitative statement that SiGe has a lower band gap than silicon.", "Hazard data: the PubChem GHS entry for germanium returned a browser check and could not be read. No SDS for a SiGe alloy was read. The germanium SDS is dated 1989 and lists no exposure limit.", "Occupational exposure limits (OSHA PEL, NIOSH REL, ACGIH TLV) for germanium or SiGe: not found. The NIOSH search returned only germanium tetrahydride.", "Critical-mineral status of germanium on the 2025 USGS list: not confirmed in the germanium chapter read for this profile. Silicon is confirmed as added to the 2025 list in the USGS silicon chapter. EU critical-materials status: not checked.", "Crustal abundance of silicon and germanium: not found in the USGS chapters read.", "Dopant levels and growth conditions for the RTG couples: the NASA report says p-type is doped with boron and n-type with phosphorus, and that traditional samples were solidified and homogenized by zone-levelling (citing Dismukes 1964). No dopant level or growth parameter is given.", "Conflict in sources: the Wikipedia RTG page says the n-leg is doped with boron and the p-leg with phosphorus. The NASA report says n-type with P and p-type with B. This profile follows the NASA report.", "Radiation, vacuum and flight data for the SiGe couples in the RTGs: not checked in this profile. Voyager power status in 2026 was not verified.", "Property names not in spores/property-canon.yaml and used here: figure_of_merit_zt, seebeck_coefficient, hot_junction_temperature, cold_junction_temperature.", "Type: the taxonomy has a SiGe type under semiconductors, which fits better than silicon. The profile uses silicon, as the brief asked, to match germanium.yaml." ], "story": { "why": "SiGe is the thermoelectric alloy used for deep-space radioisotope generators. NASA calls it a popular choice because it is high-temperature, mechanically robust and stable in air or vacuum. Alloying silicon with germanium scatters phonons and lowers lattice conductivity, which is the reason for the alloy. Its figure of merit is lower than that of lead telluride, but it tolerates hotter hot junctions. The same silicon-germanium material system is used in SiGe HBT transistors.", "uses": [ { "where": "Radioisotope generators", "line": "MHW-RTG units with SiGe couples flew on Voyager 1 and 2, and GPHS-RTG units with the same SiGe technology flew on Galileo, Ulysses, Cassini and New Horizons (Wikipedia)." }, { "where": "SiGe transistors", "line": "IHP presented a SiGe HBT with fT/fmax of 505 GHz/720 GHz at IEDM 2016. Wikipedia says the HBTs let CMOS logic be integrated into mixed-signal circuits." }, { "where": "Strain layers in CMOS", "line": "Wikipedia says SiGe is used as a strain-inducing layer for CMOS transistors." } ], "can_do": [ { "label": "Thermoelectric figure of merit", "line": "A p-type Si80Ge20B2 sample reached zT of 0.75 at 1000 K, and 0.8 with 4 wt% MnTe (Ivanova et al., 2023).", "benchmark": "figure_of_merit_zt", "scope": "material", "value": "0.75 at 1000 K" }, { "label": "Hot junction", "line": "NASA's 1968 study used SiGe hot junctions of 1089 K and 1255 K in its generator designs.", "benchmark": "hot_junction_temperature", "scope": "material", "value": "1089 to 1255 K" }, { "label": "Density in a weight model", "line": "NASA's 1968 weight model used 4.31 g/cm3 for Si-Ge elements, against a higher value for lead telluride. The value is a model input, not a measurement.", "benchmark": "density", "scope": "material", "value": "4.31 g/cm3" } ], "compare": "The NASA 1968 study says lead telluride has a higher figure of merit than Si-Ge, but a much higher density than Si-Ge (4.31 g/cm3), and it chose Si-Ge for generators with hotter hot junctions (1089 to 1255 K against 811 K for lead telluride). Against germanium on its own, the sources read here give no direct comparison of thermoelectric behaviour.", "compare_rows": [ { "label": "Density", "benchmark": "density", "scope": "material" }, { "label": "Thermoelectric figure of merit at 1000 K", "benchmark": "figure_of_merit_zt", "scope": "material" }, { "label": "Hot-junction temperature", "benchmark": "hot_junction_temperature", "scope": "material" } ], "handling": [ "Treat germanium-containing SiGe as brittle. The germanium SDS lists mechanical fracture.", "Keep it away from bromine, chlorine, fluorine, oxygen and potassium chlorate when heated, per the germanium SDS.", "Check a SiGe-specific SDS before handling, because none was read for this alloy." ], "good_for": [ "High-temperature thermoelectric legs. NASA and Wikipedia report SiGe couples in RTGs with hot junctions of 1089 to 1273 K.", "Fast RF transistors. IHP reports a SiGe HBT with fT/fmax of 505 GHz/720 GHz." ], "watch_out": [ "Figure of merit: zT is about 0.75 at 1000 K for the p-type sample read, and NASA says it is much lower than lead telluride.", "Germanium supply: about 20 percent of a Si80Ge20 alloy is germanium, and USGS reports high US import reliance.", "Grain growth at high temperature can erase the gain from nanostructuring." ], "verdict": "SiGe is well established as a high-temperature thermoelectric alloy for deep-space radioisotope generators, and as the base of SiGe transistors for fast RF chips. Ten values are sourced here, covering zT, Seebeck coefficient, junction temperatures and one design density. Thermal conductivity, melting point and density at a stated composition were not found as printed values in the pages read, and no SiGe-specific hazard data were read.", "recipe": { "line": "SiGe is an alloy of silicon and germanium in any molar ratio, written Si1-xGex (Wikipedia). The RTG thermoelectric material in the NASA report is Si1-xGex, doped with boron for p-type and with phosphorus for n-type. The 2023 paper's p-type composition is Si80Ge20B2. NASA's report describes powder processing with spark plasma sintering. Traditional samples were solidified and homogenized by zone-levelling (NASA report, citing Dismukes 1964).", "parts": [ { "name": "Silicon", "symbol": "Si", "role": "Host lattice of the alloy. Phonon scattering from the Si and Ge mass difference lowers lattice conductivity (NASA report, citing Abeles).", "share_percent": 80 }, { "name": "Germanium", "symbol": "Ge", "role": "Alloying element. Its share is the Si80Ge20 composition of the 2023 paper; the alloy is made in any Si-Ge ratio (Wikipedia).", "share_percent": 20 } ] }, "risk_groups": [ { "title": "For people", "lead": "The only SDS read is for germanium (1989), and it gives low toxicity. No SDS for the SiGe alloy was read.", "points": [ { "label": "Germanium SDS", "line": "The 1989 SDS says germanium is considered to be of low toxicity and may be a mild skin irritant. Inhalation effects are unknown." }, { "label": "Handling", "line": "Avoid heating germanium with bromine, chlorine, fluorine, oxygen or potassium chlorate, per the same SDS." } ], "level": 1, "verdict": "Low toxicity for germanium; no SiGe SDS" }, { "title": "If it fails", "lead": "The failure routes in the sources are grain growth at high temperature and germanium supply.", "points": [ { "label": "Heat", "line": "NASA says thermally induced grain growth can hinder nanostructured SiGe, because the ZT gain from small grains is lost." }, { "label": "Supply", "line": "USGS reports that US imports of germanium metal fell 67 percent in 2025, to an estimated 7,000 kg, after China's ban on exports to the United States in 2024." } ] } ] }, "updated": "2026-10-26", "review": { "status": "draft", "method": "assistant", "checked_values": 10, "unreachable": 0, "caveats": 0, "note": "Written by an AI assistant on 2026-10-26 from pages read for this profile. Ten property values are sourced. Thermal conductivity, melting point and density at a stated composition were not found as printed values." }, "sources": { "ivanova2023": { "title": "Ivanova et al., p-type SiGe-based composite produced by mechanical alloying and spark plasma sintering, Materials Letters 357 (2023), 135746", "url": "https://mdr.nims.go.jp/datasets/8ac554e7-8275-4a96-90f5-99a2ea57ef18", "kind": "paper", "license": "In Copyright (repository record); values cited, not reproduced" }, "wiki-sige": { "title": "Wikipedia, Silicon-germanium (composition, uses, thermoelectric and RTG sections)", "url": "https://en.wikipedia.org/wiki/Silicon%E2%80%93germanium", "kind": "web", "license": "page content, cited as published" }, "wiki-rtg-app": { "title": "Wikipedia, Application of silicon-germanium thermoelectrics in space exploration", "url": "https://en.wikipedia.org/wiki/Application_of_silicon-germanium_thermoelectrics_in_space_exploration", "kind": "web", "license": "page content, cited as published" }, "nasa-wsi2": { "title": "Mackey, Sehirlioglu and Dynys, WSi2 in Si1-xGex composites: processing and thermoelectric properties (NASA NTRS 20150002719)", "url": "https://ntrs.nasa.gov/citations/20150002719", "kind": "report", "license": "public domain (NASA)" }, "nasa-tmx1453": { "title": "Parametric analysis of radioisotope-thermoelectric generators, NASA Lewis TM X-1453 (1968)", "url": "https://ntrs.nasa.gov/citations/19680005161", "kind": "report", "license": "public domain (NASA)" }, "nasa-tmx1501": { "title": "Ward and Ruch, Parametric analysis of radioisotope cascaded thermoelectric generators, NASA TM X-1501 (1968)", "url": "https://ntrs.nasa.gov/citations/19680005116", "kind": "report", "license": "public domain (NASA)" }, "osaka-prb2010": { "title": "Shimura et al., Residual order in the thermal oxide of a fully strained SiGe alloy on Si, Physical Review B 81, 033308 (2010)", "url": "https://hdl.handle.net/11094/85489", "kind": "paper", "license": "Copyright 2010 American Physical Society (repository record); values cited, not reproduced" }, "ihp-2016": { "title": "IHP press release, fastest silicon-based transistor (IEDM 2016, SiGe HBT with fT/fmax of 505 GHz/720 GHz)", "url": "https://nachrichten.idw-online.de/2016/12/05/ihp-presents-the-fastest-silicon-based-transistor-in-the-world", "kind": "web", "license": "page content, cited as published" }, "usgs-si-2026": { "title": "USGS Mineral Commodity Summaries 2026, Silicon", "url": "https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-silicon.pdf", "kind": "report", "license": "public domain (USGS)" }, "usgs-ge-2026": { "title": "USGS Mineral Commodity Summaries 2026, Germanium", "url": "https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-germanium.pdf", "kind": "report", "license": "public domain (USGS)" }, "ge-msds": { "title": "Pure Tech Material Safety Data Sheet, Germanium (revision 10/89)", "url": "https://cores.research.utdallas.edu/files/2023/04/germanium.pdf", "kind": "datasheet", "license": "supplier document, linked not reproduced" } }, "license": "CC-BY-4.0", "url": "https://spacemushroom.com/profiles/silicon-germanium/" }