NASA is exploring the potential use of nuclear reactors as power sources for future space missions. These missions will require electrical components, consisting of power circuits and semiconductor devices, to be placed in close vicinity to the reactor, in the midst of a high neutron and gamma-ray radiation field. Therefore, the primary goal of this research is to examine the effects of a mixed neutron and gamma-ray radiation field on the static and dynamic electrical performance of power Schottky diodes and power MOSFETs in order to support future design efforts of radiation-hard power semiconductors and circuits.
In order to accomplish this goal, commercial Si and 4H-SiC Schottky barrier power diodes were irradiated in the mixed neutron and gamma-ray radiation field of The Ohio State University research reactor (OSURR). The forward I-V characteristics were measured before and immediately after each successive radiation dose and the carrier-removal rates were compared, on the basis of NIEL, to a previous study, for which the same diode models were irradiated with a 203 MeV proton beam. In addition, a number of SiC Schottky barrier diodes were also irradiated in the OSURR and subsequently functionally tested in half-wave rectifier circuits, for which the voltage and current waveforms in the circuit were recorded. The results from the functional testing of these half-wave rectifier circuits were analyzed using results from I-V characterization, PSpice simulations, and an analytical formulation.
In addition, boost and buck converters containing commercial power MOSFETs and Schottky diodes that were irradiated to various doses in a mixed neutron and gamma-ray radiation field, were tested. In addition to overall circuit performance in terms of output voltage and efficiency, the individual voltage and current waveforms of the MOSFET and diode in each circuit were examined. Radiation-induced changes in the switching characteristics of the MOSFETs were observed. Furthermore, changes in overall circuit performance and increased power dissipation in the MOSFETs during the over-voltage turn-off transient and on-state conduction portions of the switching cycle were observed. In addition to I-V characterization of the MOSFETs and diodes, PSpice simulations were performed in order to aid in the analysis and interpretation of the experimental results.