Polycrystalline Germanium N Type Crystal Uncoated

Germanium windows offer superior transmission capabilities in the 2-14 µm waveband, making them suitable for both mid-wave and long-wave infrared (IR) systems. As a prevalent choice in the production of IR windows and lenses, germanium is integral to thermal imaging technologies.

These high-density windows exhibit a thermal escape characteristic, where increased window temperatures lead to reduced transmission efficiency. Germanium windows are widely utilized across various sectors, including defense and aerospace industries, life and medical sciences, and industrial OEMs, among other applications requiring infrared functionality.




N-type germanium is a type of semiconductor that has been doped with elements to add extra electrons, making electrons the majority charge carriers. Below is a detailed overview of N-type germanium, including its properties, uses, and key characteristics.

Doping Elements:

  • Common Dopants: Phosphorus, arsenic, and antimony.
    • These elements have more valence electrons than germanium, contributing extra electrons to the semiconductor material.

Electrical Properties:

  • Majority Charge Carriers: Electrons.
  • Conductivity: Increased due to the abundance of free electrons.
  • Current Flow: Electrons move towards the positive terminal under an electric field, creating a flow of current.

Uses in Technology:

  • Semiconductor Devices:
    • Transistors: N-type germanium is used in the manufacture of bipolar junction transistors (BJTs) and field-effect transistors (FETs).
    • Integrated Circuits (ICs): Utilized in the production of various ICs due to its effective semiconductor properties.
  • Optical Applications:
    • Optical Storage Media: Germanium layers are vaporized under vacuum conditions to produce thin films used in CDs, DVDs, and Blu-ray discs.
    • Optical Coatings: Used in anti-reflective coatings and other optical components due to its favorable refractive index and optical properties.


  • Semiconductor Efficiency: Germanium has a higher electron mobility compared to silicon, which can improve the speed and efficiency of semiconductor devices.
  • Versatility: Functions well in both high-frequency and high-power applications, making it suitable for a wide range of electronic devices.

Comparison to Silicon:

  • Similarities:
    • Both germanium and silicon are group IV elements and act as semiconductors.
    • Used in similar applications, such as transistors and integrated circuits.
  • Differences:
    • Electron Mobility: Germanium has higher electron mobility than silicon, which can enhance device performance.
    • Thermal Properties: Germanium has a lower melting point compared to silicon (937°C vs. 1,414°C), which may influence the choice of material depending on the application.


N-type germanium is a crucial material in the field of electronics and optics. With its unique combination of metalloid properties, high electron mobility, and effectiveness in semiconductor applications, it continues to be a valuable material in advanced technology manufacturing. Its use in transistors, integrated circuits, and optical coatings highlights its versatility and importance in modern electronics and optical devices.


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General Specification
  • Material: Optical-Grade Monocrystalline Germanium ( resistivity of 5-40 ohm cm)
  • Diameter: Ranges from 12mm to 380mm
  • Length: Customizable
  • Electrical Resistivity: From 0.005Ω to 50Ω/cm
  • Crystal Purity: Between 99.999% and 99.9999%
  • Surface Roughness: From Ramax 0.2μm to 4.0μm
  • Refractive Index at 10.6μm: 4.0052
  • Absorbance at 10.6μm: ≤0.035
  • Thickness Tolerance: ± 0.10mm
  • Diameter Tolerance: +0.00/-0.05mm
  • Edge Finish: Finely ground
  • Surface Quality: 60/40 Scratch/Dig
  • Surface Flatness: ≤ 5 Fringes at 633nm
  • Parallelism: ≤ 3 Arc minutes
  • Orientation: <111>
  • Transmission Range: Covers IR wavelengths from 3 to 14 microns
  • Coating Specification: Upon Request, Anti-Reflective/Diamond-Like Carbon (AR/DLC)
  • Coating: AR coated from 3-14 microns, or DLC (Diamond-Like Carbon) in black/dark grey colour, with average transparency (Tavg) greater than 80%
  • Double-sided Anti-Reflective coating with an average transparency (Tavg) greater than 85%
A graph with a line drawn on it Description automatically generated

Here is the clearer plot of the typical transmission curve for a 1mm thick Germanium (mono-crystalline) window. The graph shows a sharp increase to 50% transmission starting from 2 µm and remains constant through 16 µm. This graph provides a visual representation of how the transmission behaves across the specified wavelength range.

Germanium Physical Properties

This table details various physical properties of the material, which could include mechanical, thermal, and electrical characteristics, relevant for applications that require precise material specifications.

the refractive index of a material Germanium

This table provides the refractive index of a material over the wavelength range from 2 micrometres to 14 micrometres, useful for applications requiring optical properties data at different IR spectrums.

optical characteristics of Germanium

This table presents various optical characteristics, including transmission spectrum, refractive index, and optical transmittance, which are crucial for understanding the performance of optical materials in specific applications, especially those involving precise wavelength requirements.

Shape Optics Diamond-Like Carbon (DLC) Coated Germanium Windows are crafted for robustness and longevity. These windows are equipped with a high-efficiency broadband anti-reflection coating on one side and a durable DLC coating on the opposite side, ensuring outstanding transmission and resistance to environmental conditions. The DLC-coated surface is engineered to endure extreme temperature fluctuations ranging from -80 to +160°F, continuous exposure to salt spray for 24 hours, salt solubility during a 24-hour immersion, and up to 5,000 wiper oscillations with a sand and slurry mixture. Moreover, ShapeOptics DLC Coated Germanium Windows comply with the MIL-C-675C standards for severe abrasion resistance.

Shape Optics offers Germanium (Ge) Windows with three options for anti-reflection coatings to cater to different infrared (IR) applications: a 3 – 5μm coating for mid-infrared use, a 3 – 12μm coating for broadband multispectral applications, and an 8 – 12μm coating for thermal imaging systems. Given germanium’s high index of refraction, approximately 4.0 across the 2 – 14μm wavelength range, applying an anti-reflection coating is crucial for achieving adequate transmission within the desired spectral region.

3 - 5μm coating for mid-infrared of Germanium

Typical transmission of a 3mm thick Ge window with BBAR (3000-5000nm) coating at 0° AOI. It indicates the coating design wavelength range, with the following specification: Ravg <3% @ 3000 - 5000nm

3mm thick Ge window

Typical transmission of a 3mm thick Ge window with BBAR (3000-12000nm) coating at 0° AOI. It indicates the coating design wavelength range, with the following specification: Ravg <5.0% @ 3 - 12μm

3mm thick Ge window with BBAR (8000-12000nm)

Typical transmission of a 3mm thick Ge window with BBAR (8000-12000nm) coating at 0° AOI. It indicates the coating design wavelength range, with the following specification: Ravg <3.0% @ 8 - 12μm

Germanium is prone to thermal runaway, a condition where its transmission efficiency declines as temperatures rise. Therefore, it is recommended to operate Shape Optics Germanium Windows at temperatures below 100°C to maintain optimal performance. Additionally, with a high density of 5.33 g/cm³, germanium windows should be carefully integrated into designs where weight sensitivity is a factor.

The material’s Knoop Hardness, at 780, is roughly double that of magnesium fluoride, making germanium windows exceptionally suitable for demanding IR applications where durable optics are essential.

  • Adhesion Test Compliant with MIL-C-675C military standards, an adhesion test involved applying a tape that meets LT-90 specifications onto the lens film layer. The tape was affixed fully and then removed vertically. This procedure was performed three times, resulting in no blistering or peeling.
  • Temperature Test In line with MIL-C-675C specifications, test pieces were subjected to temperatures of -62±1℃ and 71±1℃. After maintaining them at room temperature (16℃~32℃) for two hours, the adhesion test was repeated, confirming no film detachment.
  • Abrasion Resistance Test Conforming to MIL-C-675C and CCC-C-440 standards, the abrasion resistance test involved a gauze tester applying a minimum force of 1.0 lbs (0.45 kg) to the film. This was repeated 25 times with gauze widths of 1/4 inch (6.4mm) and 3/8 inch (9.5mm), ensuring no damage occurred to the film surface.
  • Humidity Test Under MIL-C-675C criteria, the test piece was placed in a controlled temperature and humidity chamber set to 49 ±2℃ and 95%~100% humidity for 24 hours. The film remained intact, with no peeling, scratches, or other defects.
  • Solvent and Cleaning Testing Following MIL-C-675C specifications, test pieces were exposed to room temperature conditions (16℃~32℃) and tested with acetone and alcohol for at least 10 minutes each. After air drying and subsequent cleaning with a cotton cloth soaked in alcohol, the film surface showed no signs of peeling or scratches.
  • Salt Spray Test After 100 hours in a 35°C environment with a 5% saltwater concentration, the film showed no signs of damage.

Polycrystalline Germanium:

  • Structure: Made up of many small crystalline grains or crystals, each with a different orientation.
  • Production: Easier and cheaper to produce compared to monocrystalline germanium.
  • Efficiency: Generally less efficient in electronic and photovoltaic applications because grain boundaries can scatter charge carriers, reducing their mobility.
  • Applications: Often used in less demanding electronic applications, such as infrared optics, and in some solar cells.

Monocrystalline Germanium:

  • Structure: Consists of a single, continuous crystal lattice with no grain boundaries.
  • Production: More difficult and expensive to produce as it requires precise control of the crystal growth process.
  • Efficiency: Higher efficiency in electronic and photovoltaic applications due to fewer defects and better charge carrier mobility.
  • Applications: Preferred for high-performance applications, such as in high-speed transistors, and high-efficiency solar cells.
P-Type Polycrystalline Germanium Window 11
P-Type Polycrystalline Germanium Window 16

N-type Germanium:

  • Doping: Doped with elements that have more valence electrons than germanium (group V elements like phosphorus, arsenic, or antimony).
  • Charge Carriers: The majority charge carriers are electrons.
  • Behavior: When an electric field is applied, electrons move towards the positive terminal, making it a negative type (N-type) semiconductor.
  • Applications: Used in various electronic components, including diodes, transistors, and integrated circuits.

P-type Germanium:

  • Doping: Doped with elements that have fewer valence electrons than germanium (group III elements like boron, gallium, or indium).
  • Charge Carriers: The majority charge carriers are holes (the absence of an electron).
  • Behavior: When an electric field is applied, holes move towards the negative terminal, making it a positive type (P-type) semiconductor.
  • Applications: Also used in electronic components, often in conjunction with N-type materials to create P-N junctions, which are essential for diodes, transistors, and solar cells.
  • Comparison of P-type and N-type Semiconductors:

    Dopant ElementsBoron, Gallium, IndiumPhosphorus, Arsenic, Antimony
    Majority Charge CarriersHolesElectrons
    Direction of Current FlowHoles move to negative terminalElectrons move to positive terminal