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.
All Science Journal Classification (ASJC) codes
McGarry, M. B., Franz, P., Den Hartog, D. J., Goetz, J. A., & Johnson, J. (2014). Note: Effect of photodiode aluminum cathode frame on spectral sensitivity in the soft x-ray energy band. Review of Scientific Instruments, 85(9), -. . https://doi.org/10.1063/1.4894656