Ge
Ge is a dense, high-index semiconductor crystal transmitting 2–14 µm and is the classic lens material for uncooled thermal imaging systems.
Reference datasheet — Ge is not in the instant-quote catalog. Upload your part and an engineer will quote it in this grade or suggest the closest stocked equivalent.
Values for the SC-OPT condition
Ge tempers and conditions
Ge is supplied in 5 conditions, soft to hard. SC-OPT is the default FabDigit quotes; the values on this page are for it.
Compare all 5 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
SC-OPTDefault Optical-grade single crystal | Standard choice for thermal-imaging lenses, windows and domes needing best 8–12 µm transmission and diamond-turnable surfaces. | 70 | 0 | 800 HV | 59 W/m·K | |
High-resistivity / near-intrinsic single crystal | Pick when minimum free-carrier absorption is critical — long path lengths, THz components, CO2-laser and high-power IR optics. | 70 | 0 | 800 HV | 60 W/m·K | |
Semiconductor/substrate-grade single crystal | Ga- or Sb-doped <100>/<111> wafers for III–V epitaxy and multi-junction solar cells, not for IR imaging optics. | 70 | 0 | 800 HV | 55 W/m·K | |
Single crystal with AR / diamond-like-carbon coating | Use for any real system: multilayer AR (and DLC on the outer face) removes the 36 %/surface reflection and adds rain/sand erosion resistance. | 70 | 0 | 1,800 HV | 59 W/m·K | |
Polycrystalline optical germanium | Lower-cost, large-diameter windows and non-diamond-turned optics where grain boundaries in the surface are acceptable. | 75 | 0 | 790 HV | 57 W/m·K |
What is Ge?
Ge is a dense, high-index semiconductor crystal transmitting 2–14 µm and is the classic lens material for uncooled thermal imaging systems. It is available as single-crystal and polycrystalline optical blanks, high-resistivity and semiconductor grades, and AR/DLC-coated finished optics, with thermal conductivity of 58.6 W/m·K that helps in laser optics. Absorption rises with temperature, so service is limited to about 100 °C, and the crystal is brittle with {111} cleavage and a 5.9 µm/m·K CTE. The high index makes AR coating mandatory; ZnSe is the alternative when visible-band alignment or 0.5–22 µm coverage is needed. Ge has a density of 5.32 g/cm³ (0.192 lb/in³), heavier than 93% of glass grades. It melts at 938°C (1,720 °F). Ge has a tensile strength of 70 MPa (10.2 ksi), stronger than 76% of glass grades. Elongation at break is 0% and the elastic modulus is 103 GPa (14.9 Msi).
What is Ge used for?
- thermal imaging lenses
- IR windows
- AR-coated Ge optics
- laser optics
Advantages
- Conducts heat well — 58.6 W/m·K (33.9 BTU/hr·ft·°F), better than 95% of glass grades
- Easy to machine — 45/100, better than 85% of glass grades
- Stiff — 103 GPa (14.9 Msi), better than 81% of glass grades
Limitations
- Limited service temperature — 100°C (212 °F), worse than 98% of glass grades
- High embodied carbon — 130 kg CO₂/kg, worse than 97% of glass grades
- Heavy — 5.32 g/cm³ (0.192 lb/in³), worse than 93% of glass grades
Ge properties
Typical room-temperature values for Ge-SC-OPT; bars are the position among glass grades.
Physical4
Ge has a density of 5.32 g/cm³ (0.192 lb/in³), heavier than 93% of glass grades. It melts at 938°C (1,720 °F).
Mechanical13
Ge has a tensile strength of 70 MPa (10.2 ksi), stronger than 76% of glass grades. Elongation at break is 0% and the elastic modulus is 103 GPa (14.9 Msi).
Thermal5
Ge is rated for continuous service to 100°C (212 °F). It conducts heat at 58.6 W/m·K (33.9 BTU/hr·ft·°F), better than 95% of glass grades. Thermal expansion is 5.9 µm/m·K (3.28 µin/in·°F).
Electrical3
Ge has an electrical resistivity of 0.3 Ω·m.
Chemical & Environmental2
Corrosion resistance is good (55/100), worse than 74% of glass grades.
Sustainability3
Producing a kilogram of Ge takes about 2,000 MJ of energy and emits 130 kg of CO₂ — more than 97% of glass grades. Typical recycled content is 30%.
Manufacturability2
Ge's machinability is fair (45/100, better than 85% of glass grades).
Common Calculations4
Values are nominal handbook figures for design screening. Certified mill or lot data ships with every FabDigit order on request.
Strength versus weight in the glass family
Yield strength against density for every glass grade FabDigit runs. Ge is highlighted; hover a dot for its name, or open the interactive family chart.
Working with Ge
Is Ge easy to machine?
Grind and lap with diamond abrasives, then single-point diamond turn with light depths of cut and copious coolant; it is brittle with {111} cleavage, so edges must be chamfered and clamping loads kept low.
Can Ge be welded?
Not weldable — mount by elastomeric bonding, low-stress epoxy or spring/retainer rings that accommodate its 5.9 µm/m·K CTE.
Can Ge be formed, bent or molded?
Shaped only by crystal growth (Czochralski/casting) plus subtractive optical finishing; no plastic forming at room temperature.
Ge chemical composition (wt %)
Limits by weight percent from the governing specification, written the way the spec states them — a single maximum for impurities, a range for alloying elements, and the base element as balance.
| Element | Spec limit (wt %) |
|---|---|
| Sbppb-level n-type dopant deliberately added in some crystals to set resistivity | ≈ 0 |
| Gezone-refined 5N–6N feedstock; optical grade specified by resistivity (5–40 Ω·cm) and dislocation/etch-pit density rather than by trace chemistry | ≥ 100 (balance) |
What surface finishes work on Ge?
Polishes to sub-nanometre roughness; virtually always finished with multilayer 8–12 µm AR coatings and a DLC or hard-carbon layer on exposed outer surfaces.
How much does Ge cost?
Ge is a high-cost glass ($$$$), pricier than about 78% of the materials FabDigit quotes. Part price depends far more on geometry, tolerance and quantity than on the raw stock — upload a CAD file for a live quote.
Ge — frequently asked
What is Ge used for?
Ge is typically used for thermal imaging lenses, IR windows, AR-coated Ge optics and laser optics. In short: standard 8–12 µm lens material; high index, high density; limited to ~100 °C service.
What is the tensile strength of Ge?
Ge has a typical tensile strength of 70 MPa (10.2 ksi) — stronger than 76% of glass grades. Strength varies by condition: see the 5 listed tempers.
Is Ge easy to machine?
Reasonably — machinability is rated fair (45/100, better than 85% of glass grades). Grind and lap with diamond abrasives, then single-point diamond turn with light depths of cut and copious coolant; it is brittle with {111} cleavage, so edges must be chamfered and clamping loads kept low.
Can Ge be welded?
Not weldable — mount by elastomeric bonding, low-stress epoxy or spring/retainer rings that accommodate its 5.9 µm/m·K CTE.
What surface finishes work on Ge?
Polishes to sub-nanometre roughness; virtually always finished with multilayer 8–12 µm AR coatings and a DLC or hard-carbon layer on exposed outer surfaces.
Can Ge be formed, bent or molded?
Shaped only by crystal growth (Czochralski/casting) plus subtractive optical finishing; no plastic forming at room temperature.
What is the maximum service temperature of Ge?
Ge is rated for continuous use to about 100°C (212 °F). Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
How much does Ge cost?
Ge is a high-cost glass ($$$$), pricier than about 78% of the materials FabDigit quotes. Part price depends far more on geometry, tolerance and quantity than on the raw stock — upload a CAD file for a live quote.
Sources
- ASM Handbook Vol. 2 — Properties of Nonferrous Alloys and Special-Purpose Materials (germanium) — ASM International (1990)
- Handbook of Optical Constants of Solids — Academic Press (1998)
- CRC Handbook of Chemistry and Physics, 97th ed. — CRC Press (2016)
- Germanium (Ge) IR optical material datasheet — II-VI / Coherent, Umicore, Crystran (2023)
- Landolt-Börnstein: Semiconductors — Group IV Elements, elastic constants of Ge — Springer (2001)
- Mineral Commodity Summaries — Germanium (recycling and price) — USGS (2025)
Property data is compiled from published supplier and standards handbooks and normalised for comparison; hardness values on non-Brinell scales are converted approximately for charting only. Manufacturability limits are FabDigit quote-engine defaults and may be relaxed by engineering review. Nothing on this page is a certification — request mill certs, CoC or material test reports with your order.