Space Radiation Induced Degradation Effects in Si and SiC Power Devices

Abstract

4H-Silicon carbide (SiC), a wide bandgap semiconductor, has proved its mettle in several applications such as power transmission, oil exploration and, electric vehicles. SiC is also known to be a radiation hard material making it an attractive choice for nuclear and space applications. However, when the radiation tolerance of Si and SiC device technology is compared from an electrical viewpoint, some findings in the literature are contradictory. This may be attributed to the difficulty in directly comparing Si and SiC due to the vast difference in their properties. In the present work, this gap is thoroughly addressed by investigating the radiation tolerance of both device technologies via assessing the radiation induced electrical damage in commercial Si and SiC power diodes with the same rating, making them technological alternatives of each other. Two diode ratings (650 V and 1200 V) are chosen to further study the impact of device rating on their radiation hardness. The experiments are performed using 6 MeV protons so that a uniform defect density is produced throughout the active region of the diodes, though the effect of irradiating with a lower proton energy (2 MeV) is also studied. A selective and non-destructive decapsulation recipe is specifically developed, tailored, and optimized to expose the diodes while maintaining their integrity. This is needed so that the incoming protons with relatively low energy compared to space environment, are not stopped by the packaging material. The irradiation results suggest that despite having higher carrier removal rates, SiC diodes are at least ~4.5 times more tolerant than their Si counterparts in the forward mode. This is attributed to (i) the ~2 order of magnitude lower base region doping concentration of the Si diode and (ii) the bipolar nature of the Si PiN diode which makes it susceptible to severe recombination lifetime degradation, thereby reducing its on-state resistance. Similarly, in the reverse mode, the SiC diode demonstrates superior radiation hardness due to its wider bandgap, where the leakage current after a few hours of irradiation is even lower than that measured prior to irradiation; possibly due to a proton irradiation induced ‘self-healing’ effect. Furthermore, using the displacement damage dose hypothesis, a methodology is developed to accurately extend the presented experimental results to higher particle energies present in a real space environment, without the need to perform additional experiments. Additionally, the Non Ionizing Energy Loss (NIEL) concept is utilized to develop a TCAD-based framework which can simulate the displacement damage effects in planar semiconductor devices without relying on any previous irradiation experiments. The simulation results demonstrate good agreement with the experimental data for both the Si and SiC diodes. An analytical model that enables quick calculation of carrier removal rates of Si and SiC devices is also proposed, which only requires two known parameters, namely, the doping concentration of the active region and the NIEL value of the incoming radiation. The model helps identify the key design parameter which improves the radiation tolerance of power devices against displacement damage, enabling space engineers to predict the performance of electronic devices under any particle irradiation exposure.