Materials Science Forum Vol. 1062

Abstract: 6H-SiC and 3C-SiC structural, electronic and optical properties have been calculated by applying the principles of density functional theory based on the plane wave pseudo-potential. This method is implanted in Wien2k Software. Structural parameters are calculated at the level of Perdew Burke and Ernzerhof (PBE) parameterized generalized gradient approximation (GGA). The obtained results given in Table I were compared to the experimental data in relation with the lattice constant hexagonal ration c/a and the band gap value parameters of 6H-SiC and 3C-SiC, there was a very accurate concordance. The superior gap value and the good absorption coefficient drives us to realize a p⁺nn⁺ solar cell device using SILVACO Software. The 3C-SiC material resulted in a considerable performance for photovoltaic applications.

Abstract: The 10 kV silicon carbide p-channel insulated gate bipolar transistors (IGBTs) with low forward voltage drop (V_F) have been fabricated and characterized successfully. The novel edge termination structure of Four-Region Multistep Field Limiting Rings (FRM-FLRs) and the optimum JFET region design proposed in our previous work is adopted to improve the blocking performance and the on-state characteristics. The fabricated device with a chip size of 6 mm × 6 mm and an active area of 0.16 cm² exhibits a high blocking voltage of -10 kV with a small leakage current below -200 nA. Meanwhile, a low forward voltage drop of -8 V at the collector current of -10 A with a gate bias of -20 V is obtained at room temperature, corresponding to a current density of 62.5 A/cm². Besides, a lower gate leakage current is measured less than 2 nA at the gate voltage of -30 V. Experimental results demonstrate that a better trade-off between the blocking voltage and the on-state characteristics is achieved for the fabricated device, which is desirable for the high power applications.

Abstract: In this paper, proton implantation with different combinations of MeV energies and doses from 2×10⁹ to 1×10¹¹ cm^-2 is used to create defects in the drift region of 10 kV 4H-SiC PiN diodes to obtain a localized drop in the SRH lifetime. On-state and reverse recovery behaviors are measured to observe how MeV proton implantation influences these devices and values of reverse recovery charge Q_rr are extracted. These measurements are carried out under different temperatures, showing that the reverse recovery behavior is sensitive to temperature due to the activation of incompletely ionized p-type acceptors. The results also show that increasing proton implantation energies and fluencies can have a strong effect on diodes and cause lower Q_rr and switching losses, but also higher on-state voltage drop and forward conduction losses. The trade-off between static and dynamic performance is evaluated using Q_rr and forward voltage drop. Higher fluencies, or energies, help to improve the turn-off performance, but at a cost of the static performance.

Abstract: The influence of the recovery characteristics on the switching behavior of SiC metal-oxide-semiconductor field-effect transistors (MOSFETs) with different switching speeds was investigated. A comparative analysis of the devices with different recovery characteristics revealed an increase in the turn-on loss (E_on) owing to the higher output capacitance charge (Q_oss) and reverse recovery charge (Q_rr) in the recovery arm. On the other hand, a higher Q_oss in the recovery arm resulted in a lower turn-off loss (E_off). In addition, an increase in Q_oss and Q_rr further influenced E_on and E_off at a higher switching speed. Furthermore, a higher Q_rr observed at a higher switching speed indicated a more significant impact of Q_rr on E_on at a high switching speed than that of Q_oss. The findings clarified in this study highlight the necessity of focusing the recovery characteristics to ensure a desirable switching loss of SiC MOSFETs.

Abstract: The effect of the contact resistance between the p-well and the source electrode of SiC metal-oxide-semiconductor field-effect transistors (MOSFETs) on the self-turn-on phenomenon was investigated experimentally. It was found that the contact resistance significantly affects the self-turn-on in addition to the conventional self-turn-on owing to the parasitic capacitances. To simulate this phenomenon, a circuit model including the contact resistance, p-well sheet resistance, and p-well/n+ region diode was created, and the simulation results were compared with the measurement results. Consequently, by considering the contact resistance and the forward recovery effect in the diode characteristics, the gate-induced voltage was calculated, with the results close to those of the experiment. Thus, the influence of contact resistance and p-well/n+ diode effects are clearly very important when operating SiC MOSFETs at high switching speeds.

Abstract: Due to their low leakage current, low noise levels, high thermal conductivity, and potential radiation hardness, SiC devices offer various advantages over Si devices in certain applications. As a result, they are being considered for operation in harsh environments, such as plasma diagnostic systems in future nuclear fusion reactors or in high energy physics applications. We report on relevant results of the GRACE project, which seeks to deliver a new generation of SiC sensors with graphene-enhanced contacts. Such devices are aimed to be radiation-hard and functional at high temperatures. The work presented in this paper focuses on the optimisation of the electrical contacts, along with the electrical characterisation and radiation-tolerance assessment of the first sensor prototypes produced.

Abstract: Power devices are susceptible to failure by terrestrial neutron single-event burnout (SEB) while in the high-voltage blocking state and above a V_DS threshold for that device. Typically, the SEB failure rate is measured at a high blocking voltage, with the source and gate at ground potential. Here the effect of a negative gate bias, commonly applied during MOSFET switching to the blocking state, on the SEB failure rate is examined. It is observed that the SEB failure rate is only weakly dependent on the negative gate bias, because it does not significantly affect the peak field in the drift region where avalanche breakdown is initiated. A negative gate bias of -8V_GS in the device blocking state at 1100V_DS only results in a 6% increase in the MOSFET SEB failure rate.

Abstract: Comparison of C-V characteristics and interface trap distribution for 6H-SiC MOS capacitor with AlN and HfO₂ as high-k dielectric are presented. It is observed that the transition from accumulation to inversion requires a small change in gate voltage for HfO₂ compared to AlN. Furthermore, larger shift in flat band voltage with respect to frequency is observed in case of AlN. A larger change in capacitance with respect to voltage and flat band voltage shift with respect to frequency for AlN indicated a poor choice for MOS capacitor compared to HfO₂.

Abstract: In this paper, a prototype of 6 series-connected SiC-MOSFETs for double pulses test purpose is presented. This prototype represents many challenges amongst which the measurements of voltage sharing and the EMI issues due to high dv/dt. High voltage tests are performed up to 8 kV at 65A and voltage balancing, losses and switching speeds are evaluated. Switching speed up to 520 V/ns are recorded.

Abstract: We report successful demonstration of 2kV, SiC super-junction (SJ) PiN diodes formed by deep implantation of Al and N. In our devices, alternating 12μm deep n-type and p-type SJ pillars fabricated on a 10μm pitch and result in a SJ diode with a measured blocking voltage 500V higher than comparable non-SJ diodes. Four activation anneals ranging from 1700 °C to 2000 °C were compared for effectiveness in eliminating post-implant lattice damage, and the optimum anneal condition was identified.