Umicore
Germanium Optics
Leading the way in infrared optics
Germanium Infrared Optical Materials
Umicore brings you the proven advantages of Germanium (Ge)
infrared optical materials for the manufacture of quality thermal
imaging systems. Ge provides the reliability and
reproducible properties essential to today’s rapidly expanding base
of commercial and military thermal imaging applications.
Umicore has built upon the many proven advantages of Ge to offer
you, the highest quality, the broadest possible range of sizes and
specifications and the shortest lead time in the industry.
Ge is the material of choice for systems operating in the far infrared
wavelength region, 8 to 12 microns. It is also useful at wavelengths
down to 2 microns. The chart below compares some of the more
significant characteristics of Ge and other infrared materials.
Both monocrystalline and polycrystalline Ge are available. Our
Standard Optical Grade materials are produced to optimize
transmission in the usable wavelength region. Ge has also
been shown to be a good electromagnetic interference (EMI)
shielding material. Other grades, engineered to meet your
specific requirements, are also available. Sophisticated machining
capabilities at Umicore allow for the production of optical blanks in
a wide variety of shapes and sizes, up to 24 inches in diameter, in
prototype or production quantities, as well as finished optics
(polished and coated) spherical, aspherical and asphero-diffractives.
Material
Transmittance
Available
Sizes
EMI
Performance
Rain
Erosion
Resistance
Relative
Cost
Index of
Refraction
Modulus of
Rupture
Ge
Good
Large
Good
Good
Low/Med
4.0
Med - High
Si
Good/Mid IR
Medium
Moderate
Good
Low
3.4
High
ZnS
Good
Large
Poor
Poor
Low/Med
2.2
Med
ZnSe
Good
Large
Poor
Poor
High
2.4
Low - Med
ZnS/ZnSe
Good
Medium
Poor
Poor
High
2.4
Med
GaAs
Good
Medium
Poor
Poor
High
3.0
Med
CdTe
Good
Small
Poor
Poor
High
2.7
Low
Umicore Germanium Optics 3
Properties of Germanium
Physical
Thermal
Symbol
Ge
Atomic Number
32
Atomic Weight
72.59
Crystal Structure
diamond cubic
5.323
Density, 25°C, (g/cm3)
4.416 X 1022
Atomic Density, 25°C, (atoms/cm3)
Lattice Constant, 25°C,(nm)
0.565754
Surface Tension, liquid at mp,
(mN/m, (= dyne/cm))
650
Modulus of Rupture, (MPa)
72.4
Mohs Hardness
6.3
Vickers Hardness, 25 gm load, (kg/mm ) 746 (53 ohm-cm)
Other Resistivities (See Figure Below)
1.004 (110 fracture plane)
Fracture Toughness, (MPa•m1/2) Thermal Shock Resistance
125°C
Poisson’s Ratio, 125-375 K
0.278
Natural Isotopic Abundance, (%)
mass no. 70
20.4
72
27.4
73
7.8
74
36.6
76
7.8
Elastic Constants, 25°C, (cm2/dyne)
S11 = 9.685 X 10-13
S12 = -2.70 X 10-13
S44 = 14.94 X 10-13
Elastic Coefficients, 25°C, (dynes/cm2)
C11 = 13.16 X 1011
C12 = 5.09 X 1011
C44 = 6.69 X 1011
Young’s Modulii, 25°C, (dynes/cm2)
Y100 = 10.33 X 1011
Y110 = 13.80 X 1011
Y111 = 15.55 X 1011
Shear Modulii, 25°C, (dynes/cm2)
M100 = 6.69 X 1011
M100 = 4.1 x 1011
M111 = 4.9 x 1011
Melting Point, (°C)
937.4
Boiling Point, (°C)
2830
Heat Capacity, 25°C, (J/kg•K)
322
Latent Heat of Fusion, (J/g)
466.5
Latent Heat of Vaporization, (J/g)
4602
Coefficient of Linear Expansion, (10-6/K)
100K
2.3
200K
5.0
300K
6.0
Other Temperatures
See Below
Thermal Conductivity, (W/Km)
100K
232
200K
96.8
300K
59.9
400K
43.2
Other Temperatures
See Below
Vicker’s Hardness vs. Resistivity
Vicker's Hardness (kg/mm2)
1000
950
900
850
800
750
700
0.1
1
10
Resistivity (ohm-cm)
100
Electronic
Intrinsic Resistivity, 25°C, (ohm-cm)
Intrinsic Conductivity Type
Intrinsic Electron Drift Mobility,
25°C, (cm2/Vs)
Intrinsic Hole Mobility,
25°C, (cm2/Vs)
Band Gap, minimum, (eV)
25°C
0 K
Number of Intrinsic Electrons,
25°C, (1013/cm3)
53
(n) Negative
3800
1850
0.67
0.744
2.12
Linear Thermal Expansion Coefficient and Thermal
Conductivity of Germanium vs. Temperature
6
260
220
5
Expansion
4
180
3
140
Conductivity
2
100
60
1
20
0
0
100
200
300
Temperature (K)
400
500
Thermal Conductivity (W/(m•k)
Linear Thermal Expansion Coefficient (10-6/K)
2
Strength
The thickness required to support a pressure difference may be
determined by the following equation:
Thk = (1.1 P r2 SF/MR)1/2
where P= pressure difference (PSI)
r= unsupported radius (inches)
SF= safety factor (4 to 6 suggested)
MR= modulus of rupture (PSI)
Chemical Properties
Germanium is quite stable in air up to 400°C when slow oxidation
begins. Oxidation becomes noticeably more rapid above 600°C.
The metal resists concentrated hydrochloric acid, concentrated
hydrofluoric acid and concentrated sodium hydroxide solution, even
Properties of Standard
Opical Grade Germanium
at their boiling points. It is not attacked by cold sulfuric acid, but
does react slowly in hot sulfuric acid. Nitric acid attacks Germanium
more readily than sulfuric acid at all temperatures. Germanium
Electrical
reacts readily with mixtures of nitric and hydrofluoric acids, with
Our Standard Optical Grade Ge is n-type. The resistivity of the material
molten alkalies, and more slowly with aqua regia. Germanium also
is typically in the range of 3-40 ohm-cm at 25°C. Measurements are
reacts readily with the halogens to form the respective tetrahalides.
made on each boule or casting produced according to ASTM Standards
F 42 and F 43.
Toxicology
Optical
Germanium metal is considered to have low toxicity. Inhalation of
Ge produced to these electrical specifications can provide very good
Ge dust, such as from grinding or polishing, has not been shown to
transmission in the 2-15 µm range up to about 45°C. Representative
have produced any health problem. Umicore has studied the effect
samples prepared from each boule or casting produced are tested
of Ge machining on the renal function of its coworkers, and found
with a spectro-photometer (FTIR) through the wavelength range of
no effect*. Broken Germanium is sharp and can easily cause cuts.
interest. Transmittance, and subsequently absorption coefficients, can
be determined from these measurements.
Standard Optical Grade Ge has an absorption coefficient no greater
than 0.035 cm-1 at 10.6 µm at 25°C. The table at the top of the
next page shows the minimum transmission values Umicore will
guarantee through a 1 cm thick, polished, uncoated sample and
the calculated absorption coefficients for Ge at 25°C at selected
wavelengths. Shown for comparison are theoretical maximum
transmissions based on reflection losses only.
Absorption coefficients are calculated from the thickness (t),
transmission (T), and wavelength data by the equation below:
Where r is the reflectivity of Ge at the wavelength of interest. For Ge
beyond about 1.5 µm, where the absorption index is negligible, r = (n1)2/(n+1)2, where n is the refractive index. The change in index with
* B Swennen, A Mallants, H A Roels, J P Buchet, A Bernard, RR Lauwerys,
D Lison, Occup Environ Med 2000; 57 p 242
temperature, dn/dT, from 250-350 K, is 4.0 X 10-4 K-1.
Umicore Germanium Optics 5
Guaranteed Minimum Transmission
and Maximum Absorption Coefficients of
Standard Optical Grade Ge at 25°C
Wavelength (µm)
Theoretical
Maximum
Transmission
(1 cm )
Minimum
Transmission
(1 cm)
Based upon the refractive index and
Maximum
Absorption
Coefficient
absorption coefficient of typical Optical Grade
Germanium, the total energy distribution
of a light beam approaching a Germanium
flat at normal incidence can be calculated at
-1
2.5
3
4
5
6
46.39%
46.60
46.80
46.88
46.93
45.7%
45.9
46.1
46.2
46.1
0.010 cm
0.010
0.010
0.010
0.012
7
8
9
10
10.6
11
12
13
14
46.96
46.98
47.00
47.00
47.01
47.01
47.02
47.02
47.03
45.9
45.7
45.5
45.3
45.0
44.9
37.6
38.1
38.6
0.017
0.022
0.025
0.029
0.035
0.037
0.179
0.169
0.158
any wavelength according to the following
equations:
T = [(1-r)2e-at] / [1-r2e-2at]
R = r+[(1-r)2re-2at] / [1-r2e-2at]
A = (1-r) [1-e-at] / [1-re-at]
T
R
A
r
n
a
t
=
=
=
=
=
=
=
fraction of energy transmitted
fraction of energy reflected
fraction of energy absorbed
reflectivity = [(n-1)/(n+1)]2
refractive index
absorption coefficient (cm-1)
thickness (cm)
Energy Distribution of Typical Optical Grade Germanium
Wavelength
(µm)
2.5
3.0
4.0
5.0
6.0
7.0
8.0
8.5
9.0
9.5
10.0
10.6
11.0
11.3
11.5
11.7
11.9
12.0
12.3
12.7
13.0
13.3
14.0
14.1
15.0
15.6
16.0
n
4.0653
4.0446
4.0255
4.0170
4.0122
4.0092
4.0074
4.0067
4.0061
4.0056
4.0052
4.0048
4.0045
4.0043
4.0042
4.0041
4.0040
4.0039
4.0038
4.0036
4.0035
4.0034
4.0032
4.0031
4.0029
4.0027
4.0026
Typical a
(cm-1)
.0047
.0047
.0047
.0051
.0068
.0107
.0150
.0150
.0178
.0195
.0215
.0270
.0295
.0340
.056
.130
.200
.170
.140
.133
.160
.225
.149
.147
.385
.605
.530
Refl.
53.59
53.38
53.19
53.10
53.04
52.99
52.96
52.95
52.94
52.92
52.91
52.89
52.87
52.85
52.77
52.49
52.22
52.33
52.45
52.47
52.37
52.13
52.41
52.41
51.54
50.79
51.04
Thickness = 1.0mm
Abs.
0.05
0.05
0.05
0.05
0.07
0.11
0.15
0.15
0.18
0.19
0.21
0.27
0.29
0.34
0.56
1.28
1.96
1.67
1.38
1.31
1.57
2.20
1.47
1.45
3.70
5.68
5.02
Trans.
46.36
46.57
46.77
46.85
46.89
46.90
46.89
46.90
46.89
46.88
46.87
46.84
46.83
46.81
46.68
46.23
45.82
46.00
46.18
46.22
46.06
45.68
46.13
46.14
44.76
43.53
43.94
Refl.
53.43
53.22
53.02
52.92
52.80
52.63
52.44
52.44
52.33
52.26
52.18
51.98
51.88
51.72
50.95
48.67
46.86
47.60
48.39
48.58
47.85
46.28
48.14
48.20
43.29
40.60
41.37
Thickness = 10.0mm
Abs.
Trans.
0.47
0.47
0.47
0.51
0.68
1.06
1.48
1.48
1.75
1.91
2.10
2.62
2.86
3.28
5.28
11.41
16.45
14.37
12.17
11.64
13.65
18.09
12.84
12.69
27.08
36.15
33.40
46.11
46.32
46.51
46.57
46.52
46.32
46.08
46.09
45.93
45.83
45.72
45.40
45.26
45.00
43.76
39.92
36.69
38.03
39.44
39.78
38.50
35.62
39.02
39.11
29.63
23.25
25.22
Index of Refraction at 25°C of Optical
Grade Germanium
7
One of the most important properties of
Germanium is its high refractive index,
6
making it a very useful imaging component
of IR systems operating in the 2 to 12 µm
range. Although we do not measure the
5
See expanded
view below
Umicore’s Optical Grade Germanium has been
found to have inhomogeneities of the index
below 2 X 10-4.
The transmission curve at the top of the
next page shows the typical transmission
Index of Refraction
index of refraction nor its homogeneity,
4
3
2
of Optical Grade Ge at 25°C for a polished,
uncoated sample of 10 mm thickness.
1
0.01
0.1
1
1
0
50
Wavelength (µm)
4.025
Index of Refraction
4.020
4.015
4.010
4.005
4.000
4
6
8
10
Wavelength
(Mm)
Wavelength
(µm)
12
14
16
Umicore Germanium Optics 7
Germanium Typical
Typical Transmission
Transmission
Germanium
50
% Transmission
% Transmission
40
30
20
10
0
5
10
15
Wavelength (µm)
Wavelength (µm)
25
Absorption
at 25°C of
Optical Grade
Germanium
Typical
Germanium
Coefficient
Typical
Germanium
Coefficientof
of Absorption
Absorption
3
2
1
0.9
0.8
0.7
0.6
0.5
0.4
-1
Absorption
Coefficient
Abs Coeff.
(cm-1)(cm )
20
0.3
Germanium exhibits low absorption of
0.2
infrared radiation in the usable wavelength
range of 2 to 12 µm. The band gap of
0.1
0.09
0.08
0.07
0.06
0.05
0.67 eV in Germanium is responsible for
the increase in absorption in the short
0.04
wavelength region. The lattice (phonon)
0.03
absorption bands are responsible for the
0.02
long wavelength absorption. The absorption
coefficient below 2 µm rises rapidly as
0.01
0.009
0.008
0.007
0.006
0.005
0.004
follows:
0.003
1.9 µm
0.631 cm-1
0.002
1.8
7.2
1.7
44.7
1.6
295.0
0.001
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
Wavelength
Wavelength (micron)
(µm)
19
20
21
22
23
24 25
Absorption
vs. Temperature
at 10.6
µm
Absorption
vs. Temp at 10.6
μ
Absorption Coefficient (cm )
Absorption Coefficient (cm-1-1)
1
0.1
35 ohm-cm
10
6
2
0.6
0.01
0.001
-60
-40
20
0
20
40
60
80
100
Temperature(°C)
(C)
Temperature
At high temperatures, Standard Optical
Grade Germanium is subject to excessive
absorption due to the increased number of
thermally generated holes. Germanium can
be optimized for use at 80°C or higher by
special doping to lower n-type resistivities.
This special doping makes it possible to
optimize the transmission of Ge for other
than standard optical conditions, with
minimal losses when operating at standard
conditions.
Umicore Germanium Optics 9
Absorption
vs. Temperature
at 8.0
Absorption
vs. Temp at 10.6
µ µm
Absorption Coefficient (cm-1)
Absorption Coefficient (cm-1)
1
0.1
0.01
35 ohm-cm
10
6
2
0.6
0.001
-60
-40
-20
0
20
Temperature (°C)
(C)
Temperature
40
60
80
100
Dopant Density (Sb atoms/cm3 )
2.3x1016
1
3.6 x1015
1.7x1015
3.2 x1014
1.6 x1014
100° C
-1
Absorption
Coefficient
(cm
) atµm
10.6 µm
Abs Coeff
(cm-1) at
10.6
80° C
60° C
0.1
40° C
25° C
0° C
-20° C
-40° C
-60° C
0.01
0.001
0.1
1
10
Resistivity (ohm-cm)
at 25
25°C
Resistivity
(ohm-cm) at
C
Free carrier (electron and hole) absorption and lattice (phonon)
absorption account for the IR absorption in the optical range. Holes
in Ge absorb more IR energy than electrons in this range. For nearly
electrically neutral Ge, the number of holes times the number of
electrons is constant. The number of holes present can be reduced
by increasing the number of electrons by the addition of group
V atoms (donors) to the Ge. This lowers the resistivity. Excessive
addition of donors leads to excessive electron concentration, and
increased absorption.
Umicore Germanium Optics 11
Dopant Density (Sb atoms/cm3 )
2.3x1016
3.6 x1015
1.7x1015
3.2 x1014
1.6 x1014
1
100° C
-1
Abs Coeff
(cm-1) at
10.6
Absorption
Coefficient
(cm
) atµm
8.0 µm
80° C
0.1
60° C
40° C
25° C
0.01
0° C
-20° C
-40° C
-60° C
0.001
0.1
1
10
Resistivity (ohm-cm) at 25°C
A special grade of Ge, called EMI for its ability to shield against
electromagnetic interference, has become increasingly important
for modern defence applications where other signals can be strong
enough to make nearby IR systems ineffective. By providing a Ge
window with a lower resistivity, these signals are effectively shorted
out, and the IR system functions without difficulty. Ge at EMI
resistivities will have a minimal increase in absorption compared to
Standard Optical Grade Ge.
Ge windows can also be electrically heated, for anti-icing and anti-fogging purposes,
allowing the customer to add options of window resistance and power dissipation
specifications.
Resistivity vs. Temperature
60
1000
21
oC
-10
-23
Resistivity versus
Temperature for n-type
Ge of different dopant
densities
Intrinsic
Resistivity
Resistivity(ohm-cm)
(ohm-cm)
100
10
1
0.1
0.0028
0.0030
0.0032
0.0034
0.0036
1/K
0.0038
0.0040
0.0042
Umicore Germanium Optics 13
%Transmission vs. Wavelength (24°C)
50
45
%
(0.5 cm
%Transmission
Transmission
(0.5thickness)
cm thickness)
40
35
35 ohm-cm
39 ohm-cm
30
25
14.5 ohm-cm
20
15
5.0 ohm-cm
10
2.4 ohm-cm
5
0
20
40
60
80
100
120
140
0.5 ohm-cm
160
Wavelength (μm)
Wavelength (µm)
39 ohm-cm
5.0 ohm-cm
35 ohm-cm
2.4 ohm-cm
14.5 ohm-cm
0.5 ohm-cm
The far IR transmission (20 to 160 µm) of a polished, uncoated
sample of n-type Ge of different resistivities 0.5 cm thick at 24°C is
shown above. Data not shown indicate the transmission at elevated
temperatures (about 100°C) is nearly the same (and less than 5%)
regardless of the resistivity of the material. There is a minimal
increase in transmission at lower temperatures.
Specifications for Optical Grade Germanium
Material Specifications
Dimensional Specifications
Standard
Fabricated Shapes Circular: flats, wedges, rods
Crystalline Form
Polycrystalline
Rectangular: flats, wedges, rods
Conductivity Type
n-type
Other: ellipses, spherically
Typical Resistivity
3-40 ohm-cm
generated blanks
Absorption Coefficient, at 25ºC
0.035
cm-1 max. at
10.6µm
Oxygen Content
Less than
0.03 ppm
Holes and Inclusions
Not larger than
0.002”
Premium
Crystalline Form
Monocrystalline
Resistivity Range
To customer
specification
Absorption Coefficient, at 25ºC
As low as 0.02
cm-1 at 10.6µm
Umicore provides both p and n-type Germanium with resistivities of greater than 50 ohm-cm to 0.01 ohm-cm. (This material will not necessarily
exhibit Standard Optical Grade characteristics.) Available are 1:1:1 +/-0.5° orientation monocrystalline Germanium in a range of diameters,
1:0:0+/-1.0º and 1:1:0 +/-1.0º up to 6” diameters only, as well as off-axis orientation material. Closer tolerance on orientation is available at an
additional cost.
Diameter
<100 mm +/-0.05 mm
<4.00”+/-0.002”
100 to 150 mm +/-0.13 mm 4.00 to 6.00”+/-0.005”
>150 mm +/-0.24 mm
>6.00”+/-0.010”
Thickness
+/-0.05 mm
+/-0.002”
Length and Width (less than 24 square inches in area)
+/-0.05 mm
+/-0.002”
(greater than 24 square inches in area)
+/-0.13 mm
+/-0.005”
Total Radius Sag*
</=0.05 mm
</=0.002”
Wedge
0.05 mm max. 0.002”max.
Angle
+/- 1°
+/- 1º
Bevels
0.5 mm +/-0.25 mm 0.020”+/-.010”
Surface Finish
1.27 microns max. 50 micro inches max.
Edge Finish
20 microns max. 20 microns max.
Edge Chips
<0.5 mm
<0.020”
Cropped Corners
+/-0.24 mm
+/-0.010”
Radius Corners
+/-0.64 mm
+/-0.025”
Flatness (less than 24 square inches in area)
+/-0.025 mm
+/-0.001”
(greater than 24 square inches in area)
+/-0.05 mm
+/-0.002”
Parallelism
(less than 24 square inches in area)
+/-0.64 mm
+/-0.001”
(greater than 24 square inches in area)
+/-0.05 mm
+/-0.002”
Rcc to Flat Sag
+/-0.05 mm
+/-0.002”
Truncated Cone: Radius Edge
References dimension only References dimension only
Angle vertex a minimum of 25 micron or 0.010” from large diameter
Maximum Sizes
Polycrystalline: 610 mm / 24 “ Dia; Rectangular: 559 mm x 889 mm / 22” x 35”; Generated: 610 mm / 24” Dia; Rod: 152,4 mm x 457,2 mm /
6” Dia x 18”Long
Monocrystalline: up to 241,3 mm / 9,5” Dia
* Total radius sag is dependent upon the ratio of the radius to the diameter.
Umicore Germanium Optics 15
Quality Assurance Program
Germanium Salvage Recovery
and Refining Services
Umicore customers can depend on
exceptional quality in every product
Umicore’s fully integrated refining facility
we manufacture. Umicore adheres to
offers comprehensive Ge recycling services.
international quality standards (ISO
This technology makes it possible to
9001:2000 - quality and ISO 14001:2004 -
recover and refine Ge from virtually all Ge
environment). We use the demanding EFQM
containing salvage materials and to convert
model (European Foudnation for Quality
this refined material into Optical Grade Ge
Management) for continuous improvement
blanks for our customers.
to achieve Business Excellence. These cover
the traditional client-supplier and employeremployee relationships, but also scrutinise
the company’s leadership, strategy and its
relationship to the environment and society.
Further satisfaction of your material
requirements is assured through Certificates
of Compliance, which are issued for all
products.
It is our policy to understand our customers’
expectations and requirements and to
manufacture products meeting or exceeding
those requirements in our pursuit of
continual improvement.
UMICORE OPTICAL MATERIALS
Post Office Box 737
Tel: 918-673-1650
Quapaw, Oklahoma 74363
Fax: 918-673-2121
USA
opticalmaterials@umicore.com
www.opticalmaterials.umicore.com
UMICORE ELECTRO-OPTIC MATERIALS
Watertorenstraat 33
Tel: +32 14 24 57 00
2250 Olen
Fax: +32 14 24 55 34
Belgium
optics@umicore.com
www.optics.umicore.com