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 MOSFET are studied based on 14 MeV neutron irradiation. The experimental results show that 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 positions of <i>E<sub>c</sub></i>-1.034 eV is observed after irradiation by deep level transient spectroscopy (DLTS) testing, which is corresponding to the neutron-induced defect clusters 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 result in the reduction of the Schottky barrier and the increase of the reverse leakage current. In addition, neutron-induced gate leakage increase is also observed for SiC MOSFETs. The gate current corresponding to <i>V<sub>gs</sub></i>=15 V after irradiation has increased nearly 3.3 times compared to that before irradiation. The donor type defects introduced by neutron irradiation in the oxide layer result in the alteration of the conductivity mechanism of gate oxygen 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 increase of electric field. After electrons captured by donor type defects enter the conduction band, positively charged defects are left in the gate oxide, leading to the negative shift of the transfer characteristics of SiC MOSFET. The results of DLTS testing indicate that neutron irradiation can not only cause changes in the intrinsic defect state of SiC materials near the channel of MOSFET, but also introduce new silicon vacancy defect. However, these defects are not the main cause of device performance degradation due to their low density relative to the intrinsic defects.