In situ Observation of Microstructure Evolution in 4H–SiC under 3.5 keV He⁺ Irradiation

4H–SiC was irradiated with 3.5 keV He⁺ ions using the MIAMI facility at University of Huddersfield. The evolution of microstructure and gas bubbles during the irradiation at 700 °C, 800 °C and 900 °C was observed by in situ transmission electron microscopy. Under irradiation, isolated bubbles and bubble discs formed in the SiC matrix. Bubble discs lying on {0001} and {10-10} crystal planes were beginning to form at ion fluence above 2.3 × 10²⁰ He⁺/m² at 700 °C. The density of bubble discs increased with increasing irradiation fluence. However, growth rates were different at different of the implantation periods and temperature holding periods. The nucleation and growth of the bubble discs were attributed to be coalescence of the adjacent He vacancies and combination of loop punching and trap mutation, respectively.