Investigation of electroluminescence across 4H-SiC p+/n-/n+ structures using optical emission microscopy

Studies have been conducted on the carrier recombination radiation properties across operating 4H-SiC p(+)/n-n(+) structures. Spectral and spatial distributions of the electroluminescence (EL) emitted from the cross-sectional plane of forward biased diodes were investigated by combining optical emission microscopy and imaging spectroscopy techniques. The spectral content of the luminescence across the active region was analyzed as a function of injection in a temperature range of 300-500K. At low currents deep-boron related recombination is dominating within the p-n junction region and with rising forward bias is gradually taken over by emission from the injection regions via shallow-dopant transitions. Interestingly, this band-edge EL component is found to extend deep into the substrate, apparently resulting from excess carrier diffusion and recombination. The effective diffusion length of holes was estimated from the profiles of EL penetration into the 4H-SiC substrates. The observed dissimilarity of EL penetration in different diodes is discussed considering carrier trapping and processing-induced effects.