Vacancy-Type Defects in Ion-Implanted Diamonds Probed by Monoenergetic Positron Beams

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Abstract
Vacancy-type defects introduced by 180-keV B+-, C+- and N+-ion implantation in synthesized diamonds (type Ib) were probed by the positron annihilation technique. For an unimplanted specimen, the diffusion length of positrons was shorter and the lifetime of positrons was longer than those for a type IIa specimen. These facts were attributed to the trapping or the scattering of positrons by nitrogen-related defects. For ion-implanted specimens, the depth distributions of vacancy-type defects were determined from measurements of Doppler broadening profiles of the annihilation radiation as a function of incident positron energy. The obtained profiles of defects were in agreement with those of an energy loss of ions calculated by the Monte Carlo method. From measurements of lifetime spectra of positrons, the dominant defect species introduced by the B+- or N+-ion implantation were identified as complexes of vacancy clusters and these impurities.