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Silicon Si
Silicon is used as an optical window primarily in the 3 to 5 micron band and as a substrate for production of optical filters. Large blocks of Silicon with polished faces are also employed as neutron targets in Physics experiments.
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| Transmission Range | 1.2 to 15 μm and 30 to >100 μm (1) |
| Refractive Index | 3.4223 at 5 μm (1) (2) |
| Reflection Loss | 46.2% at 5 μm (2 surfaces) |
| Absorption Coefficient | 0.01 cm-1 @ 3 μm |
| Reststrahlen Peak | n/a |
| dn/dT | 160 x 10-6/°C (3) |
| dn/dμ | 10.4 μm |
| Density | 2.33 g/cc |
| Melting Point | 1420°C |
| Thermal Conductivity | 163 W m-1 K-1 @ 273 K |
| Thermal Expansion | 2.6 x 10-6/°C @ 20°C |
| Hardness | Knoop 1150 |
| Specific Heat Capacity | 703 J Kg-1 K-1 |
| Dielectric Constant | 13 at 10 GHz |
| Young's Modulus (E) | 131 GPa (4) |
| Shear Modulus (G) | 79.9 GPa (4) |
| Bulk Modulus (K) | 102 GPa |
| Elastic Coefficients | C11 = 167; C12 = 65; C44 = 80 (4) |
| Apparent Elastic Limit | 124.1 MPa (18,000 psi) |
| Poisson Ratio | 0.266 (4) |
| Solubility | Insoluble in water |
| Molecular Weight | 28.09 |
| Class/Structure | Cubic diamond, Fd3m |
| μm | No | μm | No | μm | No |
|---|---|---|---|---|---|
| 1.357 | 3.4975 | 2.714 | 3.4358 | 6.500 | 3.4195 |
| 1.367 | 3.4962 | 3.000 | 3.4320 | 7.000 | 3.4186 |
| 1.395 | 3.4929 | 3.303 | 3.4300 | 7.500 | 3.4186 |
| 1.5295 | 3.4795 | 3.500 | 3.4284 | 8.000 | 3.4184 |
| 1.660 | 3.4696 | 4.000 | 3.4257 | 8.500 | 3.4182 |
| 1.709 | 3.4664 | 4.258 | 3.4245 | 10.00 | 3.4179 |
| 1.813 | 3.4608 | 4.500 | 3.4236 | 10.50 | 3.4178 |
| 1.970 | 3.4537 | 5.000 | 3.4223 | 11.04 | 3.4176 |
| 2.153 | 3.4476 | 5.500 | 3.4213 | ||
| 2.325 | 3.4430 | 6.000 | 3.4202 |
Silicon is grown by Czochralski pulling techniques (CZ) and contains some oxygen which causes an absorption band at 9 microns. To avoid this, Silicon can be prepared by a Float-Zone (FZ) process. Optical Silicon is generally lightly doped ( 15 to 40 ohm cm) for best transmission above 10 microns. Silicon has a further pass band 30 to 100 microns which is effective only in very high resistivity uncompensated material. Doping is usually Boron (p-type) and Phosphorus (n-type).
REFERENCES:
(1) Handbook Optical Constants, ed Palik, V1, ISBN 0-12-544420-6
(2) Li, Refractive Index of Germanium etc, J.Phys Chem, V9, p561, 1980
(3) Icenogle et al, Appl. Opt. V15, 2348 (1976)
(4) Wortman & Evans, V36, (1), P153 (1965)