Behaviour of defects in semi-insulating 4H-SiC after ultra-high temperature anneal treatments

We have recently explored the nature and stability of native defects in SI 4H-SiC after post-growth anneals between 1000 and 1800 °C from combined electron paramagnetic resonance (EPR) and low-temperature infrared photoluminescence (PL) experiments. In the present work we have extended these studies to SI 4H-SiC subjected to very high post-growth anneal temperatures (1900-2400 °C) where significantly enhanced carrier lifetimes have been recently reported for such conditions. Previously, the intensities of the V_C, V_Si, V_C-V_Si and SI-5 EPR decreased monotonically with anneals from 1200 to 1800 °C. In this work, surprisingly, many of these defects reappeared after annealing at 2100 °C and above. Similar annealing behavior was observed for the IR PL lines. Many defects are present during growth and these results illustrate the effects of the post-growth anneal treatments on their concentrations.