Specification for germanium used in infrared optics
1 Scope
This specification specifies the requirements for germanium used in infrared optics.
This specification is applicable to the germanium products used in infrared optics (hereinafter referred to as optical germanium) with wavelength range of 2.5~14.0μm.
2 Normative references
The following normative documents contain provisions which, through reference in this text, constitute provisions of this specification. For dated references, subsequent amendments (excluding corrections) to, or revisions, of any of these publications do not apply. However parties to agreements based on this specification are encouraged to investigate the possibility of applying the most recent editions of the normative documents indicated below. For undated references or references with version not indicated, the latest edition of the normative document referred to applies.
GB/T 1550 Test methods for conductivity type of extrinsic semiconducting materials
GB/T 6040 General rules for infrared analysis
GB/T 6569 Fine ceramics (advanced ceramics, advanced technical ceramics) - Test method for flexural strength of monolithic ceramics at room temperature
GB/T 26074 Germanium monocrystal - Measurement of resistivity-DC linear four-point probe
GJB 179A-1996 Sampling procedures and tables for inspection by attributes
YS/T 602 Test method for resistivity of zone-refined germanium ingot using a two-point probe
3 Requirements
3.1 Designation
The designation of optical germanium is expressed as follows:
Wherein,
M represents monocrystal, P represents polycrystal, Cz represents Czochralski growth method and DS represents directional solidification method.
Example: TR/Cz-MGe refers to germanium monocrystal used in infrared optics prepared by Czochralski growth method.
3.2 Electrical properties
3.2.1 Conductivity type
The optical germanium is of n-type conductivity.
3.2.2 Resistivity
The resistivity measuring temperature of optical germanium is (20±1)℃, and the common resistivity (ρ) is 5~30Ω·cm. Under specific conditions, the resistivity (ρ) is less than 5Ω·cm or greater than 30Ω·cm.
3.3 Optical properties
3.3.1 Transmittance
The transmittance of optical germanium is as follows:
a) At (20±3)℃, the transmittance curve of germanium monocrystal with resistivity (ρ) of 5~30Ω·cm and thickness of (5.0±0.1)mm is shown in Figure 1. The transmittance shall not be less than 39.5% at 2.5μm, not be less than 46% at 3.0~10.0μm, not be less than 45% at 11.0μm, not be less than 39.5% at 12.0μm, and not be less than 40.5% at 13.0~14.0μm.
Figure 1 Transmittance curve of optical germanium monocrystal with resistivity of 5~30Ω·cm
b) At (20±3)℃, the transmittance curve of germanium polycrystal with resistivity (ρ) of 5~30Ω·cm and thickness of (5.0±0.1)mm is shown in Figure 2. The transmittance shall not be less than 39.5% at 2.5μm, not be less than 46% at 3.0~10.0μm, not be less than 45% at 11.0μm, not be less than 39.5% at 12.0μm, and not be less than 40.5% at 13.0~14.0μm.
Figure 2 Transmittance curve of optical germanium polycrystal with resistivity of 5~30Ω·cm
c) See Figures 3 and 4 for transmittance curves of optical germanium monocrystals with resistivity of 1~5Ω·cm and resistivity greater than 30Ω·cm respectively.
Figure 3 Transmittance curve of optical germanium monocrystal with resistivity of 1~5Ω·cm
Figure 4 Transmittance curve of optical germanium monocrystal with resistivity greater than 30Ω·cm
3.3.2 Absorption coefficient
At (20±3)℃, the absorption coefficients of optical germanium shall meet those specified in Table 1.
Table 1 Absorption coefficient
Absorption coefficient Wavelength
μm
2.5 3.0 5.0 10.6 12.0 14.0
Absorption coefficient of monocrystal, cm-1 ≤0.035 ≤0.01 ≤0.015 ≤0.03 ≤0.035 ≤0.04
Absorption coefficient of polycrystal, cm-1 ≤0.04 ≤0.04 ≤0.025 ≤0.035 ≤0.04 ≤0.05
3.3.3 Refractive index
See Table 2 for reference refractive index of optical germanium at (20±1)℃.
Table 2 Refractive index of optical germanium
Wavelength, μm Refractive index Permissible deviation
3.0 4.0444 ±0.0004
4.0 4.0243
5.0 4.0154
6.0 4.0106
7.0 4.0076
8.0 4.0057
9.0 4.0044
10.0 4.0035
10.6 4.0029
11.0 4.0025
12.0 4.0020
13.0 4.0014
14.0 4.0010
3.3.4 Refractive index inhomogeneity
The refractive index inhomogeneity of germanium monocrystal shall be less than 5×10-5 and that of germanium polycrystal shall be less than 1×10-4 at a wavelength of 10.6μm.
3.3.5 Temperature coefficient of refractive index
For optical germanium, the reference temperature coefficient of refractive index is (4±0.2)×10-4 at 20~25℃.
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3.4 Bending fracture strength
The bending fracture strength of optical germanium shall not be less than 75MPa.
3.5 Dimension and permissible deviation
The dimension and permissible deviation of optical germanium shall be determined by the supplier and the purchaser through negotiation.
3.6 Appearance quality
The corner angles, edges and all surfaces of optical germanium shall be free of gaps, cracks and holes that cannot be removed by subsequent processing.
4 Quality assurance
4.1 Inspection classification
The inspections specified in this specification are quality conformance inspection.
4.2 Inspection conditions
Unless otherwise specified, inspections shall be carried out under the following conditions:
a) ambient temperature: 15~35℃;
b) relative humidity: 45%~75%;
c) atmospheric pressure: 76~106kPa.
4.3 Quality conformance inspection
The quality conformance inspection of optical germanium may be classified into Group A inspection, Group B inspection and Group C inspection. See Table 3 for inspection items.
Foreword i
1 Scope
2 Normative references
3 Requirements
4 Quality assurance
5 Delivery preparation
6 Instructions
Annex A (Normative) Test method for transmittance and absorption coefficient of optical germanium in infrared waveband
Annex B (Normative) Test method for refractive index of optical germanium
Annex C (Normative) Test method for refractive index inhomogeneity of optical germanium
