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Vertical gradient freeze gallium phosphide based optics for infrared sensors

The project aims to develop gap with a low structural defect level by using the vgf procedure. This advanced material targets micro lenses for deep infrared sensors used in monitoring of stressed structures.

The use of infrared sensors and cameras for measurement and inspection tasks is growing in industrial applications. In this context, the technical approach to deeper and deeper infrared spectral ranges calls for measuring thermally inducted changes in objectives and processes in the earlier stages, for example when used for monitoring the wheel bearings of high-speed trains. Such tasks can be carried out by infrared micro-sensors which are sensitive between 800 and 3,000 nm wavelengths, and applicable for investigations in the microscopic world. Hereby, the warranty of invariability of the micro-optical images by passing light energy through lens material is a criterion for optical quality. Essentially, interactions are afforded in connection with passing deep infrared light with high-energy density up to high-level radiation like high-performance diode lasers with high-energy density per square centimetre. Operating under conditions without significant heating requires micro-optical components that are based on material without single or multidimensional crystal dislocations. This problem addresses applications in connection with laser-aided confocal measuring procedures, or the SISCAN-method, a procedure enhanced by SIEMENS and used for measuring roughness of surfaces (Bauer, et. al., Inspect 1/2006, S. 78-79). Many semiconductor materials are optically active within the infrared spectral range between 800 and 3,000 nm and so are always usable as an infrared component. To ensure the above-mentioned criteria of quality, there is a requirement to grow semiconductor material using a crystal growth method, which is known for small crystal lattice defects. Such features provide the Vertical Gradient Freeze (VGF) method developed and well-appropriated for crystal growing procedures of semiconductor materials. The VGF method is based on crystallisation of the melt by electronically scrolling the temperature field. Unlike the current methods (Horizontal Bridgeman method /HB/ and Liquid Encapsulated Czochralski methods /LEC/), the following advantaged are expected (see ZENTRUM FUER FUNKTIONSWERKSTOFFE /ZFW/ GGMBH GOETTINGEN): * Round slices with circular features (not fulfilled by HB method); * Lower thermal gradient (1 - 5 K/cm) during the crystal growing process such as with LEC methods (60-150 K/cm) and consequently, a significantly smaller structural crystal defect density; * tuneable partial pressure of the V-component and therefore improved control of the stoichiometry and precipitation; * in-situ tempering of crystals during the cooling procedure; more efficient control of the temperature fields by multi-section heater, consequently being more economical as a result of longer crystals. comprising analysis of the ZFW (wwwuser.gwdg.de/~zfw/hlz/GAAS3.html) between commercialised LEC-GaAS and VGF material shows a ratio related to structural lattice defects (for example) of 65,000 / cmexp2 to 500 / cmexp2.
Acronym: 
INFRASENS
Project ID: 
3 869
Start date: 
01-04-2007
Project Duration: 
69months
Project costs: 
1 870 000.00€
Technological Area: 
Optical Materials
Market Area: 
Other chemicals and materials (not elsewhere classified)

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