Band-energy estimation on silicon cap annealed 4H-SiC surface using hard X-ray photoelectron spectroscopy

摘要

Silicon-cap annealing (SiCA) emerged as a promising silicidation-less ohmic contact formation method that can solve the crucial reliability limitation of ohmic contacts formed with metals; this limitation was due to carbon aggregation introduced during silicidation annealing. However, no previous study for a complete understanding of SiCA effects on the metal/SiC exists. In this study, the band-energy state of silicidation-less ohmic contacts formed by SiCA-SiC is directly estimated using hard X-ray photoelectron spectroscopy (HAXPES). The results show that Si-dot formation on the SiC surface reduces the contacts resistivity, and ohmic contact behavior is still observed even after Si-dot removal. A peak position analysis of Si 1 s orbit using HAXPES shows a clear increase in the band energy under various SiC surface conditions. Particularly, the Al/SiCA-SiC sample shows a peak shift of 0.765 eV. This strong potential barrier lowering the derived formation of the thin-depletion layer and low potential barrier on Al/SiCA-SiC junction. Moreover, the observations made using HAXPES, and transmission electron microscopy, suggest that the modification of the outer-most surface layer plays an essential role in the ohmic contact formation. These results provide insights on the ohmic contact formation mechanism for wide-band-gap semiconductor materials.