Performance of neutron-irradiated 4H-silicon carbide diodes subjected to alpha radiation

The unique electrical and material properties of 4H-silicon-carbide (4H-SiC) make it a promising candidate material for high rate particle detectors. In contrast to the ubiquitously used silicon (Si), 4H-SiC offers a higher carrier saturation velocity and larger breakdown voltage, enabling a high intrinsic time resolution and mitigating pile-up effects. Additionally, as radiation hardness requirements grow more demanding in the context of future high luminosity high energy physics experiments, wide-bandgap materials such as 4H-SiC could offer better performance due to low dark currents and higher atomic displacement thresholds. In this work, the detector performance of 50 µm thick 4H-SiC p-in-n planar pad sensors was investigated at room temperature, using an 241Am alpha source at reverse biases of up to 1100 V. Samples subjected to neutron irradiation with fluences of up to 1 × 1016 neq/cm2 were included in the study in order to quantify the radiation hardness properties of 4H-SiC. A calibration of the absolute number of collected charges was performed using a GATE simulation. The obtained results are compared to previously performed UV transient current technique (TCT) studies. Samples exhibit a drop in charge collection efficiency (CCE) with increasing irradiation fluence, partially compensated at high reverse bias voltages far above full depletion voltage. At fluences of 5 × 1014 neq/cm2 and 1 × 1015 neq/cm2, CCEs of 64 % and 51 % are obtained, decreasing to 15 % at 5 × 1015 neq/cm2. A plateau of the collected charges is observed in accordance with the depletion of the volume the alpha particles penetrate for an unirradiated reference detector. For the neutron-irradiated samples, such a plateau only becomes apparent at higher reverse bias, roughly 600 V and 900 V for neutron fluences of 5 × 1014 neq/cm2 and 1 × 1015 neq/cm2. For the highest investigated fluence, CCE behaves almost linearly with increasing reverse bias. Compared to UV-TCT measurements, the reverse bias required to deplete a sensitive volume covering full energy deposition is lower, due to the small penetration depth of the alpha particles. At the highest reverse bias, the measured CCE values agree well with earlier UV-TCT studies, with discrepancies between 1% and 5%.