Silicon vacancy-type defects in as-received and 12-MeV proton-irradiated 6H−SiC studied by positron annihilation spectroscopy

Positron lifetime spectroscopy is used to detect vacancy-related defects in as-received and 12-MeV proton-irradiated 6H-SiC crystals. We can infer from the temperature dependence of the lifetime spectra decomposition that neutral and negatively charged vacancy defects exist in crystals before and after proton irradiation at low fluence (<~4×10¹⁵H⁺cm^-2). Neutral vacancies are detected after irradiation at high fluence (>~4×10¹⁶H⁺cm^-2). Negatively charged VSi silicon monovacancies with 202±8ps lifetime are detected at low temperature in as-received n-type 6H-SiC and after irradiation at low fluence. Neutral V_Si-C divacancies associated with the (225±5)-ps lifetime are produced by irradiation and dominate the positron trapping at room temperature. In addition, different types of ionic acceptors are detected. One of them acts as a strong trapping center even at room temperature.