The effects of cyclic thermal loading on n-type 4H-SiC device components for EM-gun pulsers

This study developed and performed laboratory experiments which mimic the acute thermal cycling inflicted on device structures during high power switching for use in future EM-gun systems. Ni contacts to n-SiC were the device components selected for cyclic thermal testing. Modifications of the Ni-SiC materials properties in response to cyclic thermal fatigue were quantitatively assessed via Rutherford backscattering spectrometry (RBS), scanning electron microscopy (SEM), atomic force microscopy (AFM), surface profilometry, transmission electron microscopy (TEM) and nanoindentation testing. Decreases in nanohardness, elastic modulus and surface roughness were observed in response to thermal fatigue. No compositional modifications were observed at the metal-semiconductor interface. Our results demonstrated that the majority of the material changes were initiated after the first thermal pulse and that the effects of subsequent thermal cycling (up to 10 pulses) were negligible. The stability of the metal-semiconductor interface after exposure to repeated pulsed thermal cycling lends support for the utilization of Ni as a contact metallization for high power pulsed switching applications.