Impact of low-dose electron irradiation on n⁺p silicon strip sensors

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• 作者：The Tracker Group of the CMS Collaboration
• 关键词：Silicon strip sensors ; Charge collection ; Radiation damage ; Surface damage
• 刊名：Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment
• 出版年：2015
• 出版时间：11 December 2015
• 年：2015
• 卷：803
• 期：Complete
• 页码：100-112
• 全文大小：4602 K

文摘

The response of n⁺p silicon strip sensors to electrons from a ⁹⁰Sr source was measured using a multi-channel read-out system with 25 ns sampling time. The measurements were performed over a period of several weeks, during which the operating conditions were varied. The sensors were fabricated by Hamamatsu Photonics on 200 渭m thick float-zone and magnetic-Czochralski silicon. Their pitch was 80 渭m, and both p-stop and p-spray isolation of the n⁺ strips were studied. The electrons from the ⁹⁰Sr source were collimated to a spot with a full-width-at-half-maximum of 2 mm at the sensor surface, and the dose rate in the SiO₂ at the maximum was about 50 Gy(SiO₂)/d. After only a few hours of making measurements, significant changes in charge collection and charge sharing were observed. Annealing studies, with temperatures up to 80 °C and annealing times of 18 h showed that the changes can only be partially annealed. The observations can be qualitatively explained by the increase of the positive oxide-charge density due to the ionization of the SiO₂ by the radiation from the 尾 source. TCAD simulations of the electric field in the sensor for different oxide-charge densities and different boundary conditions at the sensor surface support this explanation. The relevance of the measurements for the design of n⁺p strip sensors is discussed.