30 September 2016 Effects on hard x-ray response of a double-sided Si strip detector caused by interstrip surface charge
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Abstract
We studied a surface effect of Double-sided Si Strip Detectors (DSSDs) in order to apply it for imaging spectroscopy of X-ray photons down to 5 keV for the first time. The Japanese cosmic X-ray satellite Hitomi, launched in February 2016, is equipped with the Hard X-ray Imager (HXI), which employs the DSSDs in 5-80 keV. In such a low energy band, the surface effect is non-negligible. When interstrip regions of p-side are irradiated, the DSSD sometimes show signals with negative pulse heights, presumably caused by positive surface charges between Si and SiO2 layers.1{5 The effect modifies the X-ray response of the HXI towards its low-energy end, below ~ 10 keV. By irradiating the DSSD with uncollimated mono-energetic X-rays of different energies, we measured the fraction of the negative events to be 2% at 26.4 keV and 30% at 6.0 keV. Using an 8 keV colli- mated X-ray beam, we directly verified that the negative events originated from the interstrip gaps on the p-side where the SiO2 layers exist. The measured energy- and position- dependences can be modeled by assuming that the negative events are produced in approximately 25 μm deep and 120 μm wide interstrip regions. When the bias voltage are halved (from 350 V to 180 V), fraction of the negative events increased by a factor of ~ 1:7, qualitatively consistent with this picture.
Conference Presentation
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Katsuma Miyake, Katsuma Miyake, Shinya Saito, Shinya Saito, Toshio Nakano, Toshio Nakano, Koichi Hagino, Koichi Hagino, Shogo Benjamin Kobayashi, Shogo Benjamin Kobayashi, Kazufumi Okuda, Kazufumi Okuda, Taketo Miura, Taketo Miura, Goro Sato, Goro Sato, Shin Watanabe, Shin Watanabe, Motohide Kokubun, Motohide Kokubun, Kazuhiro Nakazawa, Kazuhiro Nakazawa, Shinichiro Takeda, Shinichiro Takeda, Hiroyasu Tajima, Hiroyasu Tajima, Yasushi Fukazawa, Yasushi Fukazawa, Tadayuki Takahashi, Tadayuki Takahashi, "Effects on hard x-ray response of a double-sided Si strip detector caused by interstrip surface charge", Proc. SPIE 9968, Hard X-Ray, Gamma-Ray, and Neutron Detector Physics XVIII, 99680D (30 September 2016); doi: 10.1117/12.2240291; https://doi.org/10.1117/12.2240291
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