Nature effect of the gas during high temperature treatments of 4H-SiC substrates

4H-SiC seeds have been treated at high temperatures (1650-1900 deg. C) under Ar or N2 in a sublimation like graphite crucible with SiC powder at the hotter part. It was found that the surface morphology is significantly altered by the nature of the atmosphere. Surfaces without step bunching under 1 bar of N2 appear for low temperature range (≤1700 deg. C) whereas at higher temperature or lower pressure a step bunch morphology appears. Ar always gives step bunched surfaces but with more regular and parallel steps. Thermodynamical calculations performed on the Si-C-N (Ar) system show that N2 plays an important role on the gas phase chemistry of decomposition of SiC by forming gaseous species of nitrides. The theoretical results correlate well with the observations of surface morphology and graphitisation of the SiC powder