Measurement of Charge Cloud Size in X-Ray SOI Pixel Sensors

• Published in: IEEE transactions on nuclear science Vol. 66; no. 7; pp. 1897 - 1905
• Main Authors: Hagino, Kouichi, Oono, Kenji, Negishi, Kousuke, Yarita, Keigo, Kohmura, Takayoshi, Tsuru, Takeshi G., Tanaka, Takaaki, Uchida, Hiroyuki, Harada, Sodai, Okuno, Tomoyuki, Kayama, Kazuho, Amano, Yuki, Matsumura, Hideaki, Mori, Koji, Takeda, Ayaki, Nishioka, Yusuke, Fukuda, Kohei, Hida, Takahiro, Yukumoto, Masataka, Arai, Yasuo, Kurachi, Ikuo, Miyoshi, Toshinobu, Kishimoto, Shunji
• Format: Journal Article
• Language: English
• Published: New York IEEE 01.07.2019; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Astrophysics instrumentation; carrier transport; Charge measurement; charge sharing; Charge simulation; Cloud computing; Clouds; Collimation; Dependence; Detectors; Energy charge; Photoelectrons; Photonics; Photons; Pinholes; Pixels; Silicon; silicon radiation detectors; silicon-on-insulator technology; Size measurement; SOI (semiconductors); Spatial distribution; Thermal diffusion; X-ray astronomy
• ISSN: 0018-9499; 1558-1578
• DOI: 10.1109/TNS.2019.2920281

We report on a measurement of the size of charge clouds produced by X-ray photons in X-ray Silicon-on-insulator (SOI) pixel sensor named XRPIX. We carry out a beam scanning experiment of XRPIX using a monochromatic X-ray beam at 5.0 keV collimated to <inline-formula> <tex-math notation="LaTeX">\sim 10{\mathrm{ ~\mu m}} </tex-math></inline-formula> with a 4-<inline-formula> <tex-math notation="LaTeX">{\mathrm{ \mu m\phi }} </tex-math></inline-formula> pinhole and obtain the spatial distribution of single-pixel events at a subpixel scale. The standard deviation of charge clouds of 5.0-keV X-ray is estimated to be <inline-formula> <tex-math notation="LaTeX">\sigma _{\mathrm{ cloud}}=4.30\pm 0.07{\mathrm{ \,\,\mu m}} </tex-math></inline-formula>. Compared to the detector response simulation, the estimated charge cloud size is well explained by a combination of photoelectron range, thermal diffusion, and Coulomb repulsion. Moreover, by analyzing the fraction of multi-pixel events in various energies, we find that the energy dependence of the charge cloud size is also consistent with the simulation.