Ion implantation induced defects in epitaxial 4H–SiC

Thick epitaxial layers of 4H–SiC are implanted with MeV He and B ions at low doses. The epi layers are nitrogen doped and have donor concentrations around 1×1015 cm−3. The ion energies are selected to give a mean projected range of 4 μm for both He and B (1.7 and 5.0 MeV, respectively) and the implantations are performed both at nominal room temperature and 700°C. Capacitance-voltage measurements show that the samples are strongly compensated despite the low ion doses. In silicon the prompt vacancy-interstitial recombination is known to reduce the number of free migrating interstitials and vacancies with around 95%. For SiC this is not the case and the resulting concentration of implantation induced defects stable at room temperature becomes much higher than in Si. Deep level transient spectroscopy measurements between 77 and 350 K show two acceptor peaks at EC−0.18 and EC−0.67 eV (±0.03 eV), but the major part of the compensation is shown to be caused by deeper lying acceptor traps.