Development of Large-area Lithium-drifted Silicon Detectors for the GAPS Experiment. (arXiv:1812.07255v1 [astro-ph.IM])

Development of Large-area Lithium-drifted Silicon Detectors for the GAPS Experiment. (arXiv:1812.07255v1 [astro-ph.IM])
<a href="http://arxiv.org/find/astro-ph/1/au:+Kozai_M/0/1/0/all/0/1">M. Kozai</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Fuke_H/0/1/0/all/0/1">H. Fuke</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Yamada_M/0/1/0/all/0/1">M. Yamada</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Erjavec_T/0/1/0/all/0/1">T. Erjavec</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Hailey_C/0/1/0/all/0/1">C. J. Hailey</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Kato_C/0/1/0/all/0/1">C. Kato</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Madden_N/0/1/0/all/0/1">N. Madden</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Munakata_K/0/1/0/all/0/1">K. Munakata</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Perez_K/0/1/0/all/0/1">K. Perez</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Rogers_F/0/1/0/all/0/1">F. Rogers</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Saffold_N/0/1/0/all/0/1">N. Saffold</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Shimizu_Y/0/1/0/all/0/1">Y. Shimizu</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Tokuda_K/0/1/0/all/0/1">K. Tokuda</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Xiao_M/0/1/0/all/0/1">M. Xiao</a>

We have developed large-area lithium-drifted silicon (Si(Li)) detectors to
meet the unique requirements of the General Antiparticle Spectrometer (GAPS)
experiment. GAPS is an Antarctic balloon-borne mission scheduled for the first
flight in late 2020. The GAPS experiment aims to survey low-energy cosmic-ray
antinuclei, particularly antideuterons, which are recognized as essentially
background-free signals from dark matter annihilation or decay. The GAPS Si(Li)
detector design is a thickness of 2.5 mm, diameter of 10 cm and 8 readout
strips. The energy resolution of <4 keV (FWHM) for 20 to 100 keV X-rays at temperature of -35 to -45 C, far above the liquid nitrogen temperatures frequently used to achieve fine energy resolution, is required. We developed a high-quality Si crystal and Li-evaporation, diffusion and drift methods to form a uniform Li-drifted layer. Guard ring structure and optimal etching of the surface are confirmed to suppress the leakage current, which is a main source of noise. We found a thin un-drifted layer retained on the p-side effectively suppresses the leakage current. By these developments, we succeeded in developing the GAPS Si(Li) detector. As the ultimate GAPS instrument will require >1000 10-cm diameter Si(Li) detectors to achieve high sensitivity to
rare antideuteron events, high-yield production is also a key factor for the
success of the GAPS mission.

We have developed large-area lithium-drifted silicon (Si(Li)) detectors to
meet the unique requirements of the General Antiparticle Spectrometer (GAPS)
experiment. GAPS is an Antarctic balloon-borne mission scheduled for the first
flight in late 2020. The GAPS experiment aims to survey low-energy cosmic-ray
antinuclei, particularly antideuterons, which are recognized as essentially
background-free signals from dark matter annihilation or decay. The GAPS Si(Li)
detector design is a thickness of 2.5 mm, diameter of 10 cm and 8 readout
strips. The energy resolution of <4 keV (FWHM) for 20 to 100 keV X-rays at
temperature of -35 to -45 C, far above the liquid nitrogen temperatures
frequently used to achieve fine energy resolution, is required. We developed a
high-quality Si crystal and Li-evaporation, diffusion and drift methods to form
a uniform Li-drifted layer. Guard ring structure and optimal etching of the
surface are confirmed to suppress the leakage current, which is a main source
of noise. We found a thin un-drifted layer retained on the p-side effectively
suppresses the leakage current. By these developments, we succeeded in
developing the GAPS Si(Li) detector. As the ultimate GAPS instrument will
require >1000 10-cm diameter Si(Li) detectors to achieve high sensitivity to
rare antideuteron events, high-yield production is also a key factor for the
success of the GAPS mission.

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