Surface recombination velocities for 4H-SiC: Dependence of excited carrier concentration and surface passivation

Carrier lifetime plays a crucial role in optimizing the performance and reliability of SiC devices. Surface recombination is one of the factors affecting carrier lifetime. However, the reported values for surface recombination velocity (S) have been inconsistent. This study aimed to elucidate the discrepancy in S observed in various reports by conducting microwave photoconductivity decay measurements on n-type 4H-SiC freestanding epitaxial layers at different excitation carrier concentrations. Additionally, we investigated the impact of passivation by examining the surfaces subjected to oxidation and post-oxidation annealing. We observed an increase in S with increasing excited carrier concentration for the surfaces, irrespective of the crystal faces (Sand C-faces) and passivation. This suggests the presence of a potential barrier or shallow recombination centers on the surfaces. Furthermore, we observed that S remained nearly constant with increasing temperature, contrary to the behavior observed under low-injection conditions. This difference also suggests the existence of a potential barrier or shallow recombination centers on both Si- and C-faces. The comprehensive insights gained from our study have significant implications for the design of SiC devices with enhanced performance and reliability.