Positron annihilation study of divacancies in silicon illuminated by monochromatic light

The charge of divacancies in undoped float-zone silicon has been investigat ed as a function of photon energies between 0.2 and 1.2 eV by means of posi tron lifetime spectroscopy. For photon energies between 0.25 and 0.65 eV an d above 0.75 eV, negatively charged vacancies were formed, whereas in the 0 .65 to 0.75 eV range there was no effect from illumination. The results are explainable on the basis of Watkins and Corbett's model of divacancy [Phys . Rev. 138, A543 (1965)]. Evidence was found that the radioactive positron source significantly reduces the stability of the photon-induced population of negatively charged divacancies, an effect which is invoked to explain t he apparently anomalous results reported by Kawasuso and Okada [Jpn. J. App l. Phys., Part 1 36, 605 (1997)]. [S0163-1829(99)05127-9].