Observation of bias-dependent position flipping of the electric field maximum in neutron irradiated SiC diodes

This study presents an investigation of the internal electric field distribution in neutron-irradiated silicon carbide (SiC) p-in-n diodes using the Two-Photon Absorption Transient Current Technique (TPA-TCT). By analyzing the transient signal characteristics with both Weighted Prompt Current (WPC) and Time-over-Threshold (ToT) estimators, the spatial evolution of the electric field was reconstructed under varying bias conditions. After irradiation, the diodes show significant carrier trapping and a non-uniform electric field profile. A key finding is the bias-dependent flipping of the electric field maximum: under reverse bias, the field is concentrated near the front side, while under forward bias, a prominent field peak emerges at the back side. The results also indicate that the ToT-based estimator provides more robust measurements in irradiated devices, being less sensitive to signal amplitude variations and SPA contamination. These observations support the hypothesis that forward biasing enhances charge collection by repositioning the active high-field region, and they underscore the importance of field engineering in radiation-hard detector design.