Umicore Germanium Optics Leading the way in infrared optics

Transcription

1 Umicore Germanium Optics Leading the way in infrared optics

2 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

3 Umicore Germanium Optics 3 Properties of Germanium Physical Symbol Ge Atomic Number 32 Atomic Weight Crystal Structure diamond cubic Density, 25 C, (g/cm 3 ) Atomic Density, 25 C, (atoms/cm 3 ) X Lattice Constant, 25 C,(nm) 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 2 ) 746 (53 ohm-cm) Other Resistivities (See Figure Below) Fracture Toughness, (MPa m 1/2 ) (110 fracture plane) Thermal Shock Resistance 125 C Poisson s Ratio, K Natural Isotopic Abundance, (%) mass no Elastic Constants, 25 C, (cm 2 /dyne) S11 = X S12 = X S44 = X Elastic Coefficients, 25 C, (dynes/cm 2 ) C11 = X C12 = 5.09 X C44 = 6.69 X Young s Modulii, 25 C, (dynes/cm 2 ) Y100 = X Y110 = X Y111 = X Shear Modulii, 25 C, (dynes/cm 2 ) M100 = 6.69 X M100 = 4.1 x M111 = 4.9 x Thermal Melting Point, ( C) Boiling Point, ( C) 2830 Heat Capacity, 25 C, (J/kg K) 322 Latent Heat of Fusion, (J/g) Latent Heat of Vaporization, (J/g) 4602 Coefficient of Linear Expansion, (10-6 /K) 100K K K 6.0 Other Temperatures See Below Thermal Conductivity, (W/Km) 100K K K K 43.2 Other Temperatures See Below Electronic Intrinsic Resistivity, 25 C, (ohm-cm) 53 Intrinsic Conductivity Type (n) Negative Intrinsic Electron Drift Mobility, 25 C, (cm 2 /Vs) 3800 Intrinsic Hole Mobility, 25 C, (cm 2 /Vs) 1850 Band Gap, minimum, (ev) 25 C K Number of Intrinsic Electrons, 25 C, (10 13 /cm 3 ) 2.12 Linear Thermal Expansion Coefficient and Thermal Conductivity of Germanium vs. Temperature Vicker's Hardness (kg/mm 2 ) Vicker s Hardness vs. Resistivity Linear Thermal Expansion Coefficient (10-6 /K) Expansion Conductivity Thermal Conductivity (W/(m k) Resistivity (ohm-cm) Temperature (K)

4 Strength The thickness required to support a pressure difference may be determined by the following equation: Thk = (1.1 P r 2 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 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 reacts readily with mixtures of nitric and hydrofluoric acids, with molten alkalies, and more slowly with aqua regia. Germanium also reacts readily with the halogens to form the respective tetrahalides. Toxicology Germanium metal is considered to have low toxicity. Inhalation of Ge dust, such as from grinding or polishing, has not been shown to have produced any health problem. Umicore has studied the effect of Ge machining on the renal function of its coworkers, and found no effect*. Broken Germanium is sharp and can easily cause cuts. Properties of Standard Opical Grade Germanium Electrical Our Standard Optical Grade Ge is n-type. The resistivity of the material is typically in the range of 3-40 ohm-cm at 25 C. Measurements are made on each boule or casting produced according to ASTM Standards F 42 and F 43. Optical Ge produced to these electrical specifications can provide very good transmission in the 2-15 µm range up to about 45 C. Representative samples prepared from each boule or casting produced are tested with a spectro-photometer (FTIR) through the wavelength range of interest. Transmittance, and subsequently absorption coefficients, can be determined from these measurements. Standard Optical Grade Ge has an absorption coefficient no greater than 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: * B Swennen, A Mallants, H A Roels, J P Buchet, A Bernard, RR Lauwerys, D Lison, Occup Environ Med 2000; 57 p 242 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 = (n- 1) 2 /(n+1) 2, where n is the refractive index. The change in index with temperature, dn/dt, from K, is 4.0 X 10-4 K -1.

5 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) Maximum Absorption Coefficient % 45.7% cm Based upon the refractive index and 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 any wavelength according to the following equations: T = [(1-r) 2 e -at ] / [1-r 2 e -2at ] R = r+[(1-r) 2 re -2at ] / [1-r 2 e -2at ] A = (1-r) [1-e -at ] / [1-re -at ] T = fraction of energy transmitted R = fraction of energy reflected A = fraction of energy absorbed r = reflectivity = [(n-1)/(n+1)] 2 n = refractive index a = absorption coefficient (cm -1 ) t = thickness (cm) Energy Distribution of Typical Optical Grade Germanium Wavelength n Typical a (µm) (cm -1 ) Thickness = 1.0mm Refl. Abs. Trans. Thickness = 10.0mm Refl. Abs. Trans

6 Index of Refraction at 25 C of Optical Grade Germanium One of the most important properties of Germanium is its high refractive index, making it a very useful imaging component of IR systems operating in the 2 to 12 µm range. Although we do not measure the index of refraction nor its homogeneity, Umicore s Optical Grade Germanium has been found to have inhomogeneities of the index below 2 X The transmission curve at the top of the next page shows the typical transmission of Optical Grade Ge at 25 C for a polished, uncoated sample of 10 mm thickness. Index of Refraction See expanded view below Wavelength (µm) Index of Refraction Wavelength Wavelength ( m) (µm)

7 Umicore Germanium Optics 7 50 Germanium Typical Transmission 40 % Transmission % Transmission Wavelength (µm) Wavelength (µm) Typical Typical Germanium Coefficient of Absorption Absorption at 25 C of Optical Grade Germanium Absorption Coeff. Coefficient (cm -1 ) (cm -1 ) Wavelength Wavelength (micron) (µm) Germanium exhibits low absorption of infrared radiation in the usable wavelength range of 2 to 12 µm. The band gap of 0.67 ev in Germanium is responsible for the increase in absorption in the short wavelength region. The lattice (phonon) absorption bands are responsible for the long wavelength absorption. The absorption coefficient below 2 µm rises rapidly as follows: 1.9 µm cm

8 Absorption Absorption vs. Temperature vs. Temp at 10.6 at 10.6 μ µm 1 Absorption Coefficient (cm Absorption Coefficient (cm -1-1 ) ohm-cm Temperature ( C) (C) 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.

9 Umicore Germanium Optics 9 Absorption Absorption vs. Temperature vs at 8.0 µ µm 1 Absorption Coefficient (cm Absorption Coefficient (cm -1-1 ) ) ohm-cm Temperature ( C) (C)

10 Dopant Density (Sb atoms/cm 3 ) 2.3x x x x x C 80 C Absorption Coeff Coefficient (cm-1) at (cm ) at µm 10.6 µm C 40 C 25 C 0 C -20 C -40 C -60 C Resistivity (ohm-cm) at 25 CC 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.

11 Umicore Germanium Optics 11 Dopant Density (Sb atoms/cm 3 ) 2.3x x x x x C 80 C Absorption Coeff Coefficient (cm-1) at (cm ) at µm 8.0 µm C 40 C 25 C 0 C -20 C -40 C -60 C 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.

12 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 1000 C Resistivity versus Temperature for n-type Ge of different dopant densities Intrinsic 100 Resistivity Resistivity (ohm-cm) /K

13 Umicore Germanium Optics 13 %Transmission vs. Wavelength (24 C) % Transmission (0.5 cm (0.5 thickness) cm thickness) ohm-cm 39 ohm-cm 14.5 ohm-cm 5.0 ohm-cm ohm-cm ohm-cm 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.

14 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 cm -1 max. at 10.6µm Oxygen Content Less than 0.03 ppm Holes and Inclusions Not larger than 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 +/ to 150 mm +/-0.13 mm 4.00 to / >150 mm +/-0.24 mm >6.00 +/ Thickness +/-0.05 mm +/ Length and Width (less than 24 square inches in area) +/-0.05 mm +/ (greater than 24 square inches in area) +/-0.13 mm +/ Total Radius Sag* </=0.05 mm </=0.002 Wedge 0.05 mm max max. Angle +/- 1 +/- 1º Bevels 0.5 mm +/-0.25 mm /-.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 +/ Radius Corners +/-0.64 mm +/ Flatness (less than 24 square inches in area) +/ mm +/ (greater than 24 square inches in area) +/-0.05 mm +/ Parallelism (less than 24 square inches in area) +/-0.64 mm +/ (greater than 24 square inches in area) +/-0.05 mm +/ Rcc to Flat Sag +/-0.05 mm +/ Truncated Cone: Radius Edge References dimension only References dimension only Angle vertex a minimum of 25 micron or 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.

15 Umicore Germanium Optics 15 Quality Assurance Program Umicore customers can depend on exceptional quality in every product we manufacture. Umicore adheres to international quality standards (ISO 9001: quality and ISO 14001: environment). We use the demanding EFQM model (European Foudnation for Quality Management) for continuous improvement 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. Germanium Salvage Recovery and Refining Services Umicore s fully integrated refining facility offers comprehensive Ge recycling services. This technology makes it possible to recover and refine Ge from virtually all Ge containing salvage materials and to convert this refined material into Optical Grade Ge blanks for our customers. 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.

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