Study on characteristics of neutron-induced leakage current increase for SiC power devices

Abstract

In this paper, the displacement damage degradation characteristics of silicon carbide (SiC) Schottky barrier diode (SBD) and metal oxide semiconductor field effect transistor (MOSFET) are studied under 14-MeV neutron irradiation. The experimental results show that the neutron irradiation with a total fluence of 1.18×10<sup>11</sup> cm<sup>–2</sup> will not cause notable degradation of the forward <i>I-V</i> characteristics of the diode, but will lead to a significant increase in the reverse leakage current. A defect with energy level position of <inline-formula><tex-math id="Z-20230916130504">\begin{document}$ E_{\rm{C}} - 1.034 $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="18-20230976_Z-20230916130504.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="18-20230976_Z-20230916130504.png"/></alternatives></inline-formula> eV is observed after irradiation by deep level transient spectroscopy (DLTS) testing, which is corresponding to the neutron-induced defect cluster in SiC. This deep level defect may cause the Fermi level of n-type doping drift region to move toward the mid-gap level. It ultimately results in the decrease of the Schottky barrier and the increase of the reverse leakage current. In addition, neutron-induced gate leakage increase is also observed for SiC MOSFET. The gate current corresponding to <i>V</i><sub>gs</sub> = 15 V after irradiation increases nearly 3.3 times that before irradiation. The donor-type defects introduced by neutron irradiation in the oxide layer result in the difference in the conductivity mechanism of gate oxygen between before and after irradiation. The defects have an auxiliary effect on carrier crossing the gate oxide barrier, which leads to the increase of gate leakage current. The defects introduced by neutron irradiation are neutral after capturing electrons. The trapped electrons can cross a lower potential well and enter the conduction band to participate in conduction when the gate is positively biased, thus causing the gate current to increase with the electric field increasing. After electrons captured by donor-type defects enter the conduction band, positively charged defects are left from the gate oxide, leading to the negative shift of the transfer characteristics of SiC MOSFET. The results of DLTS testing indicate that the neutron irradiation can not only cause the intrinsic defect state of SiC material to change near the channel of MOSFET, but also give rise to new silicon vacancy defects. However, these defects are not the main cause of device performance degradation due to their low density relative to the intrinsic defect’s.