EPR of neutral vacancy-helium centers in silicon

In this letter we report the first observation by EPR of helium-associated defects in solid. Two new (S = 1) EPR spectra, labeled Si-AA5 and Si-AA6, arise from the association of helium and intrinsic defects in crystalline silicon. Both are produced by helium ion implantation at room temperature and are stable to 180°C. By implanting ³He isotope, the Si-AA6 ³He hyperfine spectrum has been observed. Both centers are tentatively identified as vacancy-helium centers in neutral charge states.