Materials>>Silicon window

Silicon windows, Silicon lenses, Silicon optics

Alkor Technologies produces a wide variety of Silicon Optical Components, including Silicon optical lenses, IR filters, or windows.

Silicon optical lenses are ideal for collimation or focusing applications that utilize monochromatic light. These lenses are available in a range of sizes or focal lengths for a wide variety of application needs.

Silicon optical filters, which are integrated into IR applications such as FTIR spectroscopy, are used to transmit or block a specific range of IR wavelengths.

Silicon windows are available uncoated or with a 3 - 5μm antireflection coating.

The largest dimensions of Silicon optics -up to 300mm diameter.
Silicon lenses - Dia 3mm Silicon lenses for IR LEDs, Diameter 3mm

Optical grade Silicon is normally specified with a resistivity of 10 to 40 Ohm-cm which is higher than most semiconductor applications. The usual Silicon material, unless otherwise specified is CZ, Czochralski Grade which has a Si-O absorption band at 9μm and so not important if the windows are used in the 3 to 5μm thermal band. Where required FZ, Float Zone material can be supplied which does not have this absorption.

Very high resistivity material can be supplied on special order, particularly for TeraHertz applications.

Silicon is used for windows and lenses in the 2-7µm range, ideal choice for IR LED lenses. The refractive index is near 3.4 throughout the range. Silicon high thermal conductivity and low weight are attractive features in IR or FTIR applications. Silicon is also used as a high reflectivity mirror for lasers and for IR silicon viewports.

Silicon windows transmission

Different types of Silicon are available:

  • Czochralski standard low-cost n-type (resistivity >10 Ohm*cm) or p-type (>20 Ohm*cm)
  • high resistivity Float-Zone Silicon with resistivity >1000 Ohm*cm.


Silicon properties
Chemical Formula Si
Molecular Weight 28.09
Crystal Class Cubic
Lattice Constant, 5.43
Density, g/cm3 at 293 K 2.329
Dielectric Constant for 9.37 x 109 Hz 13
Melting Point, K 1690
Thermal Conductivity, W/(m K)
at 125 K
at 313 K
at 400 K

598.6
163
105.1
Thermal Expansion, 1/K
at 75 K
at 293 K
at 1400 K

-0.5 x 10-6
2.6 x 10-6
4.6 x 10-6
Specific Heat, cal/(g K)
at 298 K
at 1800 K

0.18
0.253
Debye Temperature, K 640
Bandgap, eV 1.1
Solubility in water None
Knoop Hardness, kg/mm2 1100
Mohs Hardness 7
Young's Modulus, GPa 130.91
Shear Modulus, GPa 79.92
Bulk Modulus, GPa 101.97
Poisson's Ratio 0.28

Optical grade Silicon - index of refraction

µm    No µm    No µm    No
1.357    3.4975 1.367    3.4962 1.395    3.4929
1.5295    3.4795 1.660    3.4696 1.709    3.4664
1.813    3.4608 1.970    3.4537 2.153    3.4476
2.325    3.4430 2.714    3.4358 3.000    3.4320
3.303    3.430 3.500    3.4284 4.000    3.4257
4.258    3.4245 4.500    3.4236 5.000    3.4223
5.500    3.4213 6.000    3.4202 6.500    3.4195
7.000    3.4189 7.500    3.4186 8.000    3.4184
8.500    3.4182 10.00    3.4179 10.50    3.4178
11.04    3.4176