Effect of deep gain layer and Carbon infusion on LGAD radiation hardness

The properties of 50 μm thick Low Gain Avalanche Diode (LGAD) detectors manufactured by Hamamatsu photonics (HPK) and Fondazione Bruno Kessler (FBK) were tested before and after irradiation with neutrons. Their performance were measured in charge collection studies using $\beta$-particles from a 90Sr source and in capacitance-voltage scans (C-V) to determine the bias to deplete the gain layer. Carbon infusion to the gain layer of the sensors was tested by FBK in the UFSD3 production. HPK instead produced LGADs with a very thin, highly doped and deep multiplication layer. The sensors were exposed to a 1 MeV neutron equivalent ($n_{eq}/{cm}^2$) neutron fluence from $4\times {10}^{14}{n}_{eq}/{cm}^2$ to $4\times {10}^{15}{n}_{eq}/{cm}^2$. The collected charge and the timing resolution were measured as a function of bias voltage at $-30$ C, furthermore the profile of the capacitance over voltage of the sensors was measured. The deep gain layer (HPK-3.2) and the Carbon infusion (FBK3+C) both show reasonable performance up to $3\times {10}^{15}{n}_{eq}/{cm}^2$. Furthermore the correlation between the time resolution and the gain is found to be independent from the sensor type, given the same thickness, and from the fluence. Finally a correlation is shown between the bias voltage to deplete the gain layer and the bias voltage needed to reach a certain amount of gain in the sensor.