Germanium (Ge) SDS
Germanium (Ge) Data Sheet

Germanium is a high index material that is used to manufacture Attenuated Total Reflection (ATR) prisms for spectroscopy. Its refractive index is such that Germanium makes an effective natural 50% beamsplitter without the need for coatings. Germanium is also used extensively as a substrate for production of optical filters. Germanium covers the whole of the 8-14 micron thermal band and is used in lens systems for thermal imaging. Germanium can be AR coated with Diamond producing an extremely tough front optic.

Transmission Range
1.8 to 23 μm (1)
Refractive Index
4.0026 at 11 μm (1) (2)
Reflection Loss
53% at 11 μm (2 surfaces)
Absorption Coefficient
<0.027 cm-1 @ 10.6 μm (typical) (7)
 
0.006 cm-1 @ 5.6 μm (typical) (7)
 
<0.005 cm-1 @ 2.7 μm (7)
Reststrahlen Peak
n/a
dn/dT
+396 x 10-6 K-1 (2)(6)
dn/dμ = 0
Almost constant
Density
5.33 g/cc
Melting Point
936°C (3)
Thermal Conductivity
58.62 W m-1 K-1 @ 293 K  (6)
Thermal Expansion
6.1 x 10-6/°C @ 298 K (3)(4)(6)
Hardness
Knoop 780
Specific Heat Capacity
310 J Kg-1 K-1 (3)
Dielectric Constant
16.6 at 9.37 GHz at 300K
Youngs Modulus (E)
102.7 GPa (4)(5)
Shear Modulus (G)
67 GPa (4)(5)
Bulk Modulus (K)
77.2 GPa  (4)
Elastic Coefficients
C11 = 129 C12 = 48.3 C44 = 67.1 (5)
Apparent Elastic Limit
89.6 MPa (13000psi)
Poisson Ratio
0.28 (4)(5)
Solubility
Insoluble in water
Molecular Weight
72.59
Class/Structure
Cubic Diamond, Fd3m

 

µm No
2.058 4.102
2.153 4.0919
2.313 4.0786
2.437 4.0708
2.577 4.0609
2.714 4.0562
µm No
2.998 4.0452
3.303 4.0369
4.258 4.0216
4.866 4.017
6.238 4.0094
8.660 4.0043
µm No
9.720 4.0034
11.04 4.0026
12.00 4.0023
13.02 4.0021
   
   

Germanium is grown using the Czochralski technique by a small number of manufacturers in Belgium, USA, China and Russia. The refractive index of Germanium changes rapidly with temperature and the material becomes opaque at all wavelengths a little above 350K as the band gap floods with thermal electrons.

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) Pearson & Brattain, Proc. Inst. Radio Eng. V43, p1794, 1955
(4) Fine, J.App.Phys, V24, p338, 1953
(5) Wortman & Evans, V36, (1), P153 (1965)
(6) Hawkins, Sherwood, Djotni: Mid IR Filters for astronomical and remote sensing instrumentation. Invited Paper SPIE Conference Glasgow 2008
(7) Manufactures Published Data

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