Chemically dependent traps and polytypes at Pt/Ti contacts to 4H and 6H–SiC

We have used low energy electron-excited nanoluminescence (LEEN) spectroscopy and x-ray photoemission spectroscopy (XPS) to probe deep level defect states at interfaces of 4H and 6H–SiC with Ti/Pt metallization. These studies aim to identify process conditions under which thermally stable ohmic and Schottky contacts can be obtained on SiC while minimizing the formation of deep level electronic states. Depth-dependent LEEN measurements establish the presence of localized states and their spatial distribution on a nanometer scale. Spectra from the near interface region of 6H–SiC indicate the existence of a SiC polytype with a higher band gap of ∼3.4 eV. Excitation of the intimate metal–SiC interface reveals a process-dependent discrete state deep within the SiC band gap. XPS measurements reveal consistent differences in the C 1s chemical bonding changes with specific process steps. Analogous chemical treatments of 4H–SiC also produce a lower band gap SiC polytype with ∼2.5 eV energy extending tens of nanometers beyond the interface—confirmed by transmission electron microscopy. This work is the first to show the effect of metal–semiconductor interactions not only on localized states but also on the lattice structure of the semiconductor near the interface.