Germanium

Germanium — Material Page

View Products ↓

Germanium (Ge, atomic number 32) is a lustrous, grayish-white metalloid in Group 14 of the periodic table — the element that, more than any other, launched the semiconductor revolution. Predicted by Mendeleev in 1871 as "eka-silicon" based on gaps in his periodic table and discovered by Clemens Winkler in 1886, germanium's identification confirmed the predictive power of the periodic law. It has a diamond cubic crystal structure (like silicon and carbon-diamond), a bandgap of 0.67 eV at room temperature, and a refractive index of 4.0 in the mid-infrared — the highest of any common optical material. Germanium is brittle at room temperature (Mohs 6, no slip systems available at RT), has a density of 5.32 g/cm³, and expands slightly on solidification. It is a critical raw material designated by both the EU and US, produced primarily as a byproduct of zinc smelting (~150 tonnes/year globally) and from fly ash of coal combustion — supply is geographically concentrated in China (~70% of refinery output) and subject to periodic export restrictions.

Germanium's defining optical property is its broad infrared transparency — it transmits wavelengths from approximately 2 to 14 µm, covering both the mid-wave IR (MWIR, 3–5 µm) and long-wave IR (LWIR, 8–12 µm) atmospheric windows — making it the lens and window material of choice for thermal imaging systems. With a refractive index of ~4.0 (much higher than ZnSe at 2.4 or silicon at 3.4), germanium lenses achieve high numerical apertures in compact form factors, enabling miniaturized LWIR camera modules for automotive night vision, building envelope thermography, firefighting, and military thermal sights. Germanium's high refractive index also produces strong Fresnel reflection losses (~36% per uncoated surface), making anti-reflection coating essential for camera applications — diamond-like carbon (DLC) and ZnS AR coatings are standard. GeO₂ is the key dopant in silica optical fiber, raising the refractive index of the fiber core above the cladding to achieve total internal reflection — essentially all single-mode fiber worldwide contains a germanium-doped silica core.

In semiconductor electronics, germanium is experiencing a major renaissance as a high-mobility channel material in advanced CMOS and as the substrate for III-V multi-junction solar cells. While silicon displaced germanium in transistors by the 1960s (primarily due to GeO₂'s water solubility and inferior passivation compared to SiO₂), germanium is now returning at the leading edge: its hole mobility (~1,900 cm²/V·s, ~4× silicon) and electron mobility (~3,900 cm²/V·s, ~3× silicon) make strained Ge and SiGe channel transistors compelling for high-performance CMOS at 3 nm and below — Intel and TSMC have integrated Ge-channel pMOS in their most advanced nodes. High-purity germanium (HPGe) radiation detectors — grown as large single crystals of ultra-high purity (>10¹⁰ cm⁻³ free carrier concentration, equivalent to ~1 part in 10¹³ impurity level) — achieve energy resolution of ~0.1–0.2% for gamma rays at 1 MeV, far surpassing NaI scintillators, and are the reference instruments for nuclear safeguards, environmental radioactivity monitoring, and neutrinoless double beta decay searches using enriched ⁷⁶Ge.

General Properties

Property	Value	Notes
Atomic Number	32	Group 14 (carbon group), Period 4; metalloid; between gallium (31) and arsenic (33); the "middle" semiconductor of the classic group IV series (C, Si, Ge, Sn, Pb) with properties intermediate between silicon and tin
Atomic Mass	72.630 u	Five stable (or near-stable) isotopes spanning ⁷⁰Ge to ⁷⁶Ge; ⁷⁴Ge is the most abundant (36.50%); ⁷⁶Ge is a double beta decay candidate studied in neutrinoless double beta decay experiments (GERDA, MAJORANA)
Density (20 °C)	5.32 g/cm³	Intermediate between silicon (2.33 g/cm³) and tin (7.29 g/cm³); higher density than silicon makes Ge heavier for equivalent-size optical elements; density increases slightly on melting (liquid Ge is denser than solid, unlike Si which floats on its melt)
Melting Point	938.25 °C (1,211.40 K)	ITS-90 fixed point — the germanium melting point (938.3244 °C, on the ITS-90 scale) is one of the defined fixed points used for platinum resistance thermometer calibration; lower than silicon (1,414 °C), enabling zone refining and crystal growth at more accessible furnace temperatures
Boiling Point	2,833 °C (3,106 K)	Wide liquid range; germanium vapor pressure is negligible below ~1,000 °C; relevant to Czochralski and Bridgman crystal growth atmosphere design
Thermal Conductivity	60.2 W/m·K (at 25 °C)	Significant phonon thermal conductivity at room temperature; decreases sharply with temperature (as T⁻¹ above ~100 K) and with doping; high-purity Ge at 77 K has thermal conductivity ~1,000 W/m·K — relevant for HPGe detector cooling; isotopically enriched ⁷⁴Ge has ~40% higher thermal conductivity than natural Ge due to reduced isotope scattering
Electrical Resistivity	4.7 × 10⁻² Ω·m (intrinsic, 25 °C)	Intrinsic (undoped) semiconductor; resistivity is orders of magnitude lower than silicon (intrinsic resistivity ~640 Ω·m) due to Ge's smaller bandgap (0.67 eV vs. Si 1.12 eV) and higher intrinsic carrier concentration (~2.4 × 10¹³ cm⁻³ vs. Si 1.5 × 10¹⁰ cm⁻³ at 300 K); HPGe requires cooling to 77 K to achieve detector-grade resistivity
Crystal Structure	Diamond cubic (Fd3̄m); a = 5.658 Å	Identical structure to silicon-diamond and carbon-diamond; tetrahedral sp³ bonding; 8 atoms per unit cell; lattice parameter 5.658 Å (vs. Si 5.431 Å), ~4.2% larger than Si — enabling SiGe alloy epitaxy with tunable lattice parameter and bandgap; no allotropic transformations at ambient pressure

Mechanical Properties

Property	Value	Notes
Hardness	Mohs 6; ~780 HV Vickers	Hard but brittle — no ductile deformation at room temperature; cleaves along {111} planes; handled and machined with diamond tools; IR optical components are susceptible to impact damage and thermal shock; harder than optical glasses (Mohs 5–6) but much less tough
Elastic (Young's) Modulus	103 GPa	Slightly lower than silicon (130 GPa) and significantly lower than diamond (1,050 GPa); anisotropic — modulus varies with crystal orientation; relevant to design of Ge wafer handling systems and IR lens mounts that must accommodate differential thermal expansion between Ge and metal housings
Poisson's Ratio	0.28	Similar to silicon (0.28) and glass (0.20–0.28); relevant to finite element analysis of Ge optical element stress under mounting loads and thermal gradients
Fracture Toughness	~0.6 MPa·m½	Very low fracture toughness — germanium is substantially more brittle than silicon (~0.9 MPa·m½) and much more brittle than optical glasses (~0.7–1.0 MPa·m½); the lowest fracture toughness of any commonly used IR optical material; thermal shock resistance is poor — rapid temperature changes must be avoided in optical system design

Thermal & Environmental Properties

Property	Value	Notes
Stability in Air	Stable at RT; oxidizes above ~550 °C	Germanium forms a native GeO₂ layer (~1–2 nm) in air at room temperature; the oxide is stable and passivates the surface adequately for most applications; above ~550 °C in air, GeO₂ growth accelerates; above ~710 °C, GeO (volatile, bp 710 °C) begins to sublime — unlike SiO₂ which is fully refractory, limiting Ge use in high-temperature oxidizing environments
Acid / Alkali Resistance	Resistant to HCl, dilute H₂SO₄, HF; dissolved by HNO₃, aqua regia, H₂O₂/NH₄OH	More chemically resistant than silicon to many acids; resistant to HF (unlike SiO₂ which dissolves in HF, Ge/GeO₂ is not readily etched by HF alone); dissolved by oxidizing acid mixtures; used in selective etching of Si/Ge heterostructures in semiconductor processing
Optical Transmission	Transparent 2–14 µm (MWIR and LWIR)	Broad IR transparency across both atmospheric windows; refractive index n ≈ 4.0 at 10 µm (temperature-dependent: dn/dT = +400 ppm/°C — the highest of any common IR material, causing significant focus shift with temperature in uncooled thermal cameras); opaque below ~1.8 µm (above the bandgap energy); used without cooling in passive thermal imaging
Bandgap	0.67 eV (indirect, at 300 K); direct gap 0.80 eV at Γ	Indirect bandgap like silicon; the direct gap at the Γ point is only 130 meV above the indirect gap — strained Ge and GeSn alloys can convert the indirect gap to direct, enabling Ge-based light emission and photodetectors integrated on silicon photonic platforms; bandgap decreases with temperature (–3.7 × 10⁻⁴ eV/K)

Chemical Properties

Property	Value / Behavior	Notes
Surface Oxide	GeO₂ (hexagonal, rutile, or amorphous); GeO (volatile)	Hexagonal GeO₂ (mp 1,115 °C) is the stable bulk oxide; rutile-type GeO₂ is metastable above ~1,033 °C; native GeO₂ on Ge surfaces is water-soluble (unlike SiO₂) — a critical distinction that prevented Ge from becoming the dominant transistor material in the 1960s and remains a surface passivation challenge for Ge-channel CMOS
Oxidation States	+4 (primary, GeO₂, GeCl₄); +2 (GeO, GeS, GeCl₂)	Ge⁴⁺ is strongly dominant; GeCl₄ is the key precursor for GeO₂ fiber optic dopant deposition (MCVD, OVD, PCVD processes); GeBr₄ and GeH₄ (germane) are MOCVD/CVD precursors for Ge thin-film deposition; Ge²⁺ is a less stable state found in chalcogenide glasses (GeSe₂, GeS₂) used for IR fiber optics
Semiconductor Properties	p-type dopants: B, Al, Ga, In; n-type: P, As, Sb	Doping behavior analogous to silicon; carrier mobility: electrons ~3,900 cm²/V·s, holes ~1,900 cm²/V·s (both ~3–4× silicon values); SiGe alloys with 10–30% Ge content are the standard base material for HBT and MOSFET strain engineering in advanced CMOS foundries (TSMC, Samsung, Intel); pure Ge-channel pMOS transistors are in production at Intel 4/3 nm nodes
IR Refractive Index	n ≈ 4.003 at 10.6 µm (25 °C)	Highest refractive index of any common IR optical material; enables high-NA lenses and beam-shaping optics in compact form; the large dn/dT (+400 ppm/°C) means athermalization (passive optical compensation for focus shift with temperature) is essential in uncooled thermal camera design — addressed through lens-housing material selection and diffractive optical element combinations

Identifier	Value
Symbol	Ge
Atomic Number	32
CAS Number	7440-56-4
UN Number	Not classified (bulk metal/metalloid)
EINECS Number	231-164-3

Isotope	Type	Notes
⁷⁰Ge	Stable	20.57% natural abundance; I = 0; enriched ⁷⁰Ge has ~40% higher thermal conductivity than natural Ge due to reduced isotope-mass-disorder phonon scattering — isotopically purified ⁷⁰Ge single crystals are used in fundamental phonon transport research and as reference materials for isotopic thermal conductivity studies
⁷²Ge	Stable	27.45% natural abundance; I = 0; used as an enriched spike isotope for germanium IDMS quantification in environmental and geological samples by ICP-MS; the ⁷²Ge/⁷⁴Ge isotope ratio is used as a geochemical tracer for Ge cycling in rivers, hydrothermal systems, and the ocean
⁷³Ge	Stable	7.75% natural abundance; I = 9/2, NMR-active; ⁷³Ge NMR spectroscopy probes germanium coordination environments in germanate glasses, zeolite frameworks, and organogermanium compounds; low natural abundance and large quadrupole moment make sensitivity poor — typically requires high-field instruments and isotopic enrichment for practical NMR
⁷⁴Ge	Stable	36.50% natural abundance; most abundant germanium isotope; I = 0; the primary reference isotope for Ge isotope ratio measurements; ⁷⁴Ge/⁷⁰Ge and ⁷⁴Ge/⁷²Ge ratios (δ⁷⁴Ge) measured by MC-ICP-MS are used as proxies for continental weathering, hydrothermal alteration, and biological uptake in marine geochemistry
⁷⁶Ge	Radioactive*	7.73% natural abundance; t½ > 10²¹ yr (double beta decay candidate); the target isotope in neutrinoless double beta decay (0νββ) experiments — GERDA (Gran Sasso), MAJORANA Demonstrator (SURF), and the next-generation LEGEND experiments use enriched ⁷⁶Ge HPGe detectors to search for 0νββ at the 2,039 keV Q-value; observation of 0νββ would establish neutrinos as Majorana fermions and explain the matter-antimatter asymmetry of the universe

Scientific & Research Applications

Use Case	Form Typically Used	Description
High-Purity Ge (HPGe) Gamma Detectors	HPGe single crystals (6N+, >10¹⁰ cm⁻³ carrier purity, cooled to 77 K)	HPGe detectors achieve energy resolution of ~0.1–0.2% FWHM at 1.33 MeV (⁶⁰Co) — approximately 20× better than NaI(Tl) scintillators — and are the reference standard for nuclear gamma spectroscopy. Used in nuclear safeguards and nonproliferation verification (IAEA inspections), environmental radioactivity monitoring, nuclear security (radiological/nuclear threat detection), and as calibration references for all other gamma detection systems. Coaxial, planar, and BEGe (broad energy germanium) configurations cover energies from ~3 keV to >10 MeV.
Neutrinoless Double Beta Decay Searches	Enriched ⁷⁶Ge HPGe crystals (86–88% ⁷⁶Ge enrichment)	The GERDA experiment at LNGS (Gran Sasso) and MAJORANA Demonstrator at SURF used enriched ⁷⁶Ge HPGe detectors to search for 0νββ at the 2,039 keV Q-value, setting half-life limits of T½ > 1.8 × 10²⁶ yr. The successor LEGEND-200 (200 kg of enriched Ge) is currently operating at Gran Sasso; LEGEND-1000 (1 tonne) is planned. If observed, 0νββ would establish lepton number violation, confirm neutrinos are Majorana particles, and provide a mechanism for leptogenesis explaining cosmic matter-antimatter asymmetry.
IR Spectroscopy Windows & ATR Crystals	Ge single crystal windows, Ge ATR prisms (45° and 60° cut)	Germanium ATR (attenuated total reflectance) crystals provide a broad FTIR spectral window from 600 to 5,500 cm⁻¹ — the widest of any common ATR material. The high refractive index (n = 4.0) gives 45° Ge ATR crystals an effective sampling depth of only ~0.65 µm at 1,000 cm⁻¹, making Ge ATR the preferred choice for strongly absorbing samples (liquids, polymer films, biological tissues, foods). Used on essentially all modern FTIR instruments for rapid attenuated total reflection sampling.
SiGe HBT & Channel Research	Ge wafers, SiGe epitaxial layers on Si substrates	SiGe heterojunction bipolar transistors (HBTs) achieve fT and fmax exceeding 700 GHz — the fastest silicon-based transistors — by incorporating a graded SiGe base layer (10–30% Ge) that creates a built-in electric field accelerating minority carrier transit. Used in 5G millimeter-wave power amplifiers, automotive radar ICs (77 GHz), and high-speed optical transceiver driver circuits. Pure Ge-channel pMOS transistors with hole mobility >1,900 cm²/V·s are integrated in Intel's leading-edge CMOS processes.
Thermoelectric Devices (RTGs)	SiGe alloy pellets (Si₀.₇Ge₀.₃, p-type and n-type)	Silicon-germanium thermoelectric alloys (SiGe, ~30% Ge) were the power source for NASA deep-space missions including Voyager 1 and 2, Cassini, New Horizons, and Curiosity/Perseverance Mars rovers — operating as radioisotope thermoelectric generators (RTGs) converting ²³⁸Pu decay heat to electricity at ~700–900 °C hot-side temperatures where SiGe achieves ZT ~0.5–0.7, superior to other thermoelectrics in this temperature range.
ITS-90 Temperature Calibration	High-purity Ge metal (≥5N) in sealed calibration cells	The germanium melting point (938.3244 °C on ITS-90) is a defined fixed point of the International Temperature Scale of 1990, used for calibrating platinum resistance thermometers (Type S and R thermocouples) in the range 630–1,064 °C. High-purity Ge (≥99.999%) sealed in fused silica or graphite cells provides the reproducible melting plateau at national metrology institutes worldwide.

Industrial & Commercial Applications

Sector	Form / Compound Used	Description
Infrared Thermal Imaging Optics	Ge single crystal lenses, windows, domes (AR-coated)	Germanium lenses and windows (AR-coated with DLC or ZnS) are the standard optical elements in LWIR thermal cameras for automotive night vision (Tier 1 suppliers: Umicore, Tydex), building diagnostics, firefighting, maritime surveillance, and industrial process monitoring. Ge accounts for ~20–25% of global germanium consumption. The high refractive index (n = 4.0) enables compact, fast optics but requires careful athermalization design because dn/dT = +400 ppm/°C causes significant focus shift across the operating temperature range of uncooled microbolometer cameras.
Optical Fiber (GeO₂ Dopant)	GeCl₄ (germanium tetrachloride, optical fiber process)	GeO₂ is the primary dopant for raising the refractive index of silica optical fiber cores above the cladding, enabling total internal reflection and guided wave propagation. GeCl₄ vapor is oxidized inside the preform tube (MCVD, PCVD) or outside (OVD, VAD) during fiber manufacture. Essentially all single-mode telecommunications fiber (G.652, G.654, G.657 standards) uses a GeO₂-doped core; global fiber production exceeds 500 million km/year, making this the single largest end-use of germanium (~30% of total consumption).
III-V Multi-Junction Solar Cells	Ge substrates (150 mm wafers, 6N purity)	Germanium wafers are the standard substrate for triple-junction III-V solar cells (InGaP/GaAs/Ge) used in space solar panels on communications satellites, Earth observation spacecraft, and solar-electric propulsion systems. The Ge substrate forms the bottom junction (~0.67 eV), and its lattice parameter (5.658 Å) closely matches GaAs (5.653 Å), enabling pseudomorphic epitaxial growth of the upper junctions without excessive dislocation generation. Space solar cell production consumes ~5% of global germanium demand.
PET Scanner Detector Components	Bismuth germanate (BGO, Bi₄Ge₃O₁₂) scintillator crystals	Bismuth germanate (BGO) scintillator crystals are used as gamma detector elements in PET (positron emission tomography) scanners — detecting the 511 keV annihilation photons from positron-emitting radiotracers. BGO has high density (7.13 g/cm³) and high effective atomic number (Zeff = 75), providing excellent 511 keV photon stopping efficiency in compact detector rings. While largely replaced by faster LYSO and LSO scintillators in modern total-body PET systems, BGO is experiencing a revival in time-of-flight PET due to its prompt Cherenkov photon component.
Polyethylene Terephthalate (PET Plastic) Catalyst	GeO₂ (germanium dioxide) polycondensation catalyst	Germanium dioxide is used as a polycondensation catalyst in the production of high-clarity PET polyester resin — particularly for specialty optical-clarity grades used in water bottles, food packaging, and optical fiber buffer coatings where the clarity advantage over antimony-catalyzed PET justifies the cost premium. Ge-catalyzed PET produces a cleaner, less tinted polymer than Sb₂O₃-catalyzed material and avoids antimony regulatory concerns. This application consumes ~10–15% of global germanium production.
Infrared Chalcogenide Glass & Fiber	GeSe₂, GeS₂, Ge-As-Se, Ge-Sb-Se glasses	Germanium-based chalcogenide glasses (GeSe₂, Ge-As-Se, Ge-Sb-Se systems) transmit from 1 to 16+ µm — extending beyond the cut-off of crystalline Ge — and can be drawn into flexible IR optical fibers for chemical sensing, laser power delivery (CO₂ laser at 10.6 µm), and minimally invasive medical diagnostics. Chalcogenide glass IR optics are also used in low-cost thermal camera lenses molded by precision glass pressing, competing with single-crystal Ge at lower cost and higher volume.

Purity

Main Use

99.999% (5N)

Optical applications and general electronics — suitable for IR window and lens fabrication (thermal imaging optics), ATR crystal production, GeO₂ fiber optic dopant precursor synthesis, and SiGe thermoelectric alloy preparation where total metallic impurity levels below 10 ppm are required but ultra-high purity HPGe detector specifications are not

99.9999% (6N)

Infrared optics, high-performance semiconductors, and radiation detectors — the standard purity for HPGe gamma detector crystal growth (Czochralski or zone refining, achieving <10¹⁰ cm⁻³ free carrier concentration), MBE effusion cell loading for Ge-channel CMOS research, space solar cell substrate wafer production, and enriched ⁷⁶Ge crystal growth for neutrinoless double beta decay experiments

Synonym / Alternative Name	Context
Ge	Chemical symbol
Germanium metal	Standard commercial designation for the elemental form; distinguishes from germanium compounds (GeO₂, GeCl₄, GaAs-substrate Ge, etc.) in trade and regulatory contexts
Elemental germanium	Scientific term used to distinguish the pure element from germanium-containing materials and compounds in geochemistry, materials science, and semiconductor processing literature
HPGe (High-Purity Germanium)	Specific designation for ultra-high purity germanium used in radiation detector applications — typically zone-refined or Czochralski-grown material with net impurity concentration <10¹⁰ atoms/cm³ (one impurity atom per ~10¹³ Ge atoms), requiring operation at 77 K to suppress intrinsic carrier generation
Eka-silicon	Historical name used by Mendeleev in 1871 when predicting the existence and properties of germanium based on gaps in his periodic table — one of the most famous predictions in the history of chemistry, confirmed when Clemens Winkler discovered the element in 1886 in the mineral argyrodite (Ag₈GeS₆)
Germanium (5N / 6N)	Trade notation specifying purity: 5N = 99.999%, 6N = 99.9999%; the purity designation is critical in optical, semiconductor, and detector applications where impurity concentrations at the ppb–ppt level affect carrier mobility, optical absorption, and radiation detector energy resolution

My Wish List

Last Added Items

You have no items in your wish list.

Services

Applications

No minimum order

Free shipping included

Customized Materials

99% stock availability