Calculation of positron annihilation characteristics of six main defects in 6H -SiC and the possibility to distinguish them experimentally

We have determined positron annihilation characteristics (lifetime and Doppler broadening) in six basic vacancy-type defects of $6H$-SiC and two nitrogen-vacancy complexes using ab initio calculations. The positron characteristics obtained allow us to point out which positron technique in the most adapted to identify a particular defect. They show that the coincidence Doppler broadening technique is the most relevant for observing the silicon vacancy--nitrogen complexes, ${\mathrm{V}}_{\mathrm{Si}}{\mathrm{N}}_{\mathrm{C}}$, and carbon vacancy--carbon antisite ones, ${\mathrm{V}}_{\mathrm{C}}{\mathrm{C}}_{\mathrm{Si}}$. For the other studied defects, the calculated positron characteristics are found to be too close for the defects to be easily distinguished using a single positron annihilation technique. Then it is required to use complementary techniques, positron annihilation based or other.