  Low Gain Avalanche Diode (LGAD) is applied for the High-Granularity Timing
Detector (HGTD), and it will be used to upgrade the ATLAS experiment. The first
batch IHEP-IME LGAD sensors were designed by the Institute of High Energy
Physics (IHEP) and fabricated by the Institute of Microelectronics (IME). Three
IHEP-IME sensors (W1, W7 and W8) were irradiated by the neutrons up to the
fluence of 2.5 x 10^15 n_eq/cm^2 to study the effect of the shallow carbon and
deep N++ layer on the irradiation hardness. Taking W7 as a reference, W1 has an
extra shallow carbon applied, and W8 has a deeper N++ layer.
