Neutron Radiation induced Effects in 4H-SiC PiN Diodes

Silicon carbide (SiC) is a wide band gap semiconductor and an attractive candidate for applications in harsh environments such as space, fusion, or future high luminosity colliders. Due to the large band gap, the leakage currents in SiC devices are extremely small, even after irradiation to very high fluences, enabling operation without cooling and at high temperatures. This study investigates the effect of neutron irradiation on 50$\mu$m p-n 4H-SiC diodes using current-voltage, capacitance-voltage, and charge collection efficiency (CCE) measurements up to neutron fluences of $1\times 10^{16}$ n$_{\text{eq}}$/cm$^2$. The leakage currents of the investigated devices remained extremely small, below 10 pA at 1.1 kV reverse bias. In the forward bias, a remarkable drop of the current was observed, which was attributed to an increased epi resistivity due to compensation of the epi layer doping by deep-level defects. The CCE was evaluated for alpha particles from a radioactive source, a 62.4 MeV proton beam at the MedAustron ion therapy center and using UV-TCT. The charge collection efficiency in reverse bias was shown to scale directly with the 1 MeV equivalent fluence $\Phi_{\text{eq}}$ as $\text{CCE} \propto \Phi_{\text{eq}}^{-0.63\pm0.01}$. A CCE better than 50% was able to be obtained for fluences up to $1 \times 10^{15}$ n$_{\text{eq}}$/cm$^2$. Because of the low currents in the forward direction, particle detection was also possible in forward bias, where the CCE was found to be increased relative to reverse bias. Furthermore, a significant dependency on the amount of injected charge was observed, with the CCE surpassing 100% in alpha and UV-TCT measurements, requiring further systematic investigation.