Note: Effect of photodiode aluminum cathode frame on spectral sensitivity in the soft x-ray energy band

• Published in: Review of scientific instruments 2014-09, Vol.85 (9), p.096105-096105
• Main Authors: McGarry, M B, Franz, P, Den Hartog, D J, Goetz, J A, Johnson, J
• Format: Article
• Language: English
• Subjects: 70 PLASMA PHYSICS AND FUSION TECHNOLOGY; ALUMINIUM; Aluminum; BREMSSTRAHLUNG; CATHODES; Electron energy; ELECTRON TEMPERATURE; High temperature plasmas; HOT PLASMA; INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND TECHNOLOGY; KEV RANGE; MST DEVICE; PHOTODIODES; RADIATION DETECTORS; Scientific apparatus & instruments; SENSITIVITY; SIGNALS; SILICON; SOFT X RADIATION; Soft x rays; Spectral sensitivity; Toruses; X ray spectra; X-RAY DETECTION
• ISSN: 0034-6748; 1089-7623
• DOI: 10.1063/1.4894656

Silicon photodiodes used for soft x-ray detection typically have a thin metal electrode partially covering the active area of the photodiode, which subtly alters the spectral sensitivity of the photodiode. As a specific example, AXUV4BST photodiodes from International Radiation Detectors have a 1.0 μm thick aluminum frame covering 19% of the active area of the photodiode, which attenuates the measured x-ray signal below ~6 keV. This effect has a small systematic impact on the electron temperature calculated from measurements of soft x-ray bremsstrahlung emission from a high-temperature plasma. Although the systematic error introduced by the aluminum frame is only a few percent in typical experimental conditions on the Madison Symmetric Torus, it may be more significant for other instruments that use similar detectors.