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Proceedings Paper

Materials investigation of gallium arsenide for direct converting energy sensitive x-ray detectors
Author(s): Michael Kroening; Igor Besse; Tilo Baumbach; Axel Berthold; R. G. Melkadze; T. M. Lezhneva; L. B. Khvedelidze; G. D. Kalandadze
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Paper Abstract

For the last decade a tremendous development in the field of imaging radiation detectors has taken place. Conventional X-ray film has been replaced by digital X-ray imaging systems in a number of ways. Such systems mainly consist of silicon charge coupled devices (CCDs) where incident photons create electron-hole pairs in the thin silicon absorption layer near the surface. In contrast to visible light, which is absorbed within a 2 μm layer of silicon, the penetration of X-ray is much deeper due to higher photon energy. This disadvantage is often circumvented by the use of a scintillator absorption layer. Due to scattering of the low energy fluorescence photons, resolution and contrast of the X-ray images decrease. In order to eliminate these disadvantages, hybrid detectors consisting of direct converting semiconductors and readout electronics parts are fabricated. For this configuration, it is advantageous that both parts can be optimized separately and different materials can be used. Because of the well developed technology, the readout chip is fabricated out of silicon. As absorbing material, silicon is less suitable. In a silicon substrate of 500 μm thickness, only 15% of a 30 keV radiation is absorbed and converted into charges. In order to increase the absorption, materials with a higher atomic mass have to be used. Several compound semiconductors can be used for this purpose. One of them is GaAs, which is available as high quality semiinsulating wafer material. For detector optimization, GaAs wafers from several manufacturers with different properties were investigated. Test structures with Schottky and PIN diodes were fabricated. The I/V curves of the diodes, the spectral response from 5 up to 150 keV, the carrier concentration, and the carrier mobility were measured and compared. A survey of the results and the criteria for material selection resulting from these measurements will be provided in the paper.

Paper Details

Date Published: 9 May 2005
PDF: 8 pages
Proc. SPIE 5770, Advanced Sensor Technologies for Nondestructive Evaluation and Structural Health Monitoring, (9 May 2005); doi: 10.1117/12.601907
Show Author Affiliations
Michael Kroening, Fraunhofer Institute for Non-Destructive Testing (Germany)
Igor Besse, Fraunhofer Institute for Non-Destructive Testing (Germany)
Tilo Baumbach, Forschungszentrum Karlsruhe (Germany)
Axel Berthold, Fraunhofer Institute for Non-Destructive Testing (Germany)
R. G. Melkadze, Tbilisi State Univ. (Georgia)
T. M. Lezhneva, Tbilisi State Univ. (Georgia)
L. B. Khvedelidze, Tbilisi State Univ. (Georgia)
G. D. Kalandadze, Tbilisi State Univ. (Georgia)

Published in SPIE Proceedings Vol. 5770:
Advanced Sensor Technologies for Nondestructive Evaluation and Structural Health Monitoring
Norbert Meyendorf; George Y. Baaklini; Bernd Michel, Editor(s)

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