Y. Tabuki

Effects of the Fermi Level on Defects in Be+-Implanted GaAs Studied by a Monoenergetic Positron Beam

Vacancy-type defects in 60-keV Be+-implanted GaAs(100) were studied by a monoenergetic positron beam. The depth distribution of vacancy-type defects in an n-type specimen (Si, 1×1016 Si/cm3) was obtained from measurements of Doppler broadening profiles of the positron annihilation as a function of incident positron energy. The dominant defect species was identified as a divacancy from the characteristic value of the line-shape parameter S. These defects, however, could not be observed in the p-type specimen (Zn, 3×1018 Zn/cm3). This fact can be attributed to the recombination of vacancy-type defects and interstitial Ga atoms introduced by the Fermi level effect.

Damage to the Silicon Substrate by Reactive Ion Etching Detected by a Slow Positron Beam

Defects in reactive ion-etched Si have been investigated by means of a slow positron beam. A thin carbon-containing film (<30 A) was formed on the Si surface after reactive ion etching (RIE). Vacancy-type defects, which were estimated to distribute over 1200 A in depth by numerical fitting using the positron trapping model, were observed in the damaged subsurface region of Si. Aside from ion bombardment, ultraviolet radiation is also presumed to affect the formation of vacancies, interstitials in oxide and the formation of vacancies in Si substrate. The ionization-enhanced diffusion (IED) mechanism is expected to promote the diffusion of vacancies and interstitials into Si substrate.

Defect Annihilation in Czochralski-Grown Silicon During Out-Diffusion Process Probed with Variable-Energy Positron Beam

The defect annihilation in CZ-crystal was first detected during the process of oxygen out-diffusion, by the positron measurements with a variable-energy beam. The defects, which were related to oxygen atoms such as oxygen cluster, were mainly annihilated at the high temperature, ex., 1150°C. The defect concentration was decreasing down to one tenth, compared with that for an as-grown crystal.

Defect Formation by Ion Implantation in Cz-Si Studied by a Monoenergetic Positron Beam

Vacancy-type defects in ion implanted Si were studied by a monoenergetic positron beam. The depth-distributions of the defects were obtained from measurements of Doppler broadening profiles of the positron annihilation as a function of incident positron energy. The results showed that a size of vacany-clusters introduced by 150-keV P + -ion implantation was found to be smaller than that introduced by 2-MeV P + -ion implantation. This was attributed to an overlap of collision cascades in low-energy (150 keV) ion implanted specimens. From isochronal annealing experiments for 80-keV B + - and 150-keV P + -ion implanted specimens, the defected region was removed by 1200 °C annealing, however, for 2-MeV P + -implanted specimen, two-types of oxygen-vacancy complexes were found to coexist even after 1200 °C annealing.