  In this paper, we report on the radiation resistance of 50-micron thick LGAD
detectors manufactured at the Fondazione Bruno Kessler employing several
different doping combinations of the gain layer. LGAD detectors with gain layer
doping of Boron, Boron low-diffusion, Gallium, Carbonated Boron and Carbonated
Gallium have been designed and successfully produced. These sensors have been
exposed to neutron fluences up to $\phi_n \sim 3 \cdot 10^{16}\; n/cm^2$ and to
proton fluences up to $\phi_p \sim 9\cdot10^{15}\; p/cm^2$ to test their
radiation resistance. The experimental results show that Gallium-doped LGADs
are more heavily affected by initial acceptor removal than Boron-doped LGAD,
while the presence of Carbon reduces initial acceptor removal both for Gallium
and Boron doping. Boron low-diffusion shows a higher radiation resistance than
that of standard Boron implant, indicating a dependence of the initial acceptor
removal mechanism upon the implant width. This study also demonstrates that
proton irradiation is at least twice more effective in producing initial
acceptor removal, making proton irradiation far more damaging than neutron
irradiation.
