Effects of Shallow Carbon and Deep N++ Layer on the Radiation Hardness of IHEP-IME LGAD Sensors

Low-gain avalanche diode (LGAD) is the chosen technology for the ATLAS high-granularity timing detector (HGTD). According to previous studies, the acceptor removal effect due to the radiation and the single-event burnout (SEB) at high bias voltages are still a challenge for the LGAD. The Institute of High Energy Physics (IHEP), Beijing, China, cooperated with the Institute of Microelectronics (IME), Beijing, China, for the design and fabrication of the IHEP-IME LGAD sensors with shallow carbon and deep N++ layer to improve the radiation hardness of LGAD. After neutron irradiation up to
$2.5 \times 10^{15}\,\,{\mathrm{ n}}_{\mathrm{ eq}}$
/cm
²
, the leakage current, the collected charge, and timing resolution of the three IHEP-IME sensors measured with a beta telescope setup meet the HGTD requirements (
$< 125~\mu \text{A}$
/cm
²
, >4 fC, and <70 ps). The LGAD sensor with shallow carbon had the lowest operation voltage after irradiation and is very promising to avoid the SEB effect. A sensor with a deep N++ layer increased the breakdown voltage of the LGAD with a high dopant concentration, which could alleviate the problem of the early breakdown of radiation-hard LGAD before irradiation.