Lattice recovery and microstructural defects in thermally annealed phosphorous and aluminum implanted (0001) 4H-SiC

We report on the lattice strain and crystal defects generated in thermally annealed phosphorus and aluminum implanted (0001) 4° off-axis oriented homoepitaxial (0001)-4H-SiC (ion energy range between 30 and 200 keV). The partial crystal lattice recovery of the ion-implanted subsurface layer was achieved by thermal annealing processes in an inert gas atmosphere (Ar) in the temperature range between 1675 and 1825 °C, while the annealing time was kept constant at 15 (or 30) min. The lattice strain in ion-implanted 4H-SiC prior to and after thermal treatments was investigated in detail by high-resolution x-ray diffraction and reciprocal space mapping measurements. The thermal annealing processes reduce the lattice strain by a factor of 7, from 11.6 × 10−3 to about 1.6 × 10−3, and occur only along the [0001] axis, while the in-plane strain is negligible (< ±3 × 10−5) for all samples prior and after annealing. The determined lattice strain shows that the crystal lattice is not completely recovered, as also revealed by transmission electron microscopy observations and photoluminescence measurements. The thermal annealing induces and promotes the formation of point defect aggregates (mainly carbon-related vacancies, interstitials, and antisites) and nanoclusters with an average size between 5 and 20 nm.