Defects in ion-implanted GaN and their annealing properties were studied by using monoenergetic positron beams. Doppler broadening spectra of the annihilation radiation and the positron lifetimes were measured for Si+, O+, and Be+-implanted GaN grown by the metal-organic chemical vapor deposition technique. First-principles calculations were also used to identify defect species introduced by the implantation. For as-implanted samples, the major defect species was identified as Ga vacancies and/or divacancies. An agglomeration of defects starts after annealing at 400 °C, and the defect profile shifted toward the surface with the open volumes of the defects increasing. The annealing properties of defects were found to depend on the ion species, and they are discussed here in terms of defect concentrations and interactions between impurities and defects.
Annealing behaviours of defects in electron-irradiated diamond were studied using the positron annihilation technique. For a type IIa specimen after 3 MeV electron irradiation with a dose of 1 × 1018 cm-2, the major species of vacancy-type defects was determined to be neutral monovacancies, V0. The trapping rate of positrons by V0 decreased above 600 °C annealing, but the annihilation mode of positrons trapped by vacancy-type defects was observed even after 900 °C annealing. For a type Ib specimen after the irradiation, the major species of vacancy-type defects was determined to be negative monovacancies, and the formation of nitrogen-monovacancy pairs, N-V, was observed after 650 °C annealing. The annihilation probability between positrons and electrons with a broad momentum distribution was found to be increased by the trapping of positrons by N-V.
Positron annihilation was used to probe vacancies in Cu films deposited by Ta/SiO2/Si using electroplating and sputtering techniques. During room temperature grain growth (i.e., self-annealing) of the Cu films, two different types of vacancies (small vacancy clusters such as divacancies and large vacancy agglomerates) were introduced into grains; the formation of such defects was enhanced by residual impurities. For electroplated Cu, isochronal annealing experiments revealed further agglomeration of vacancies when annealing was done below 300 °C, and these agglomerates started to dissociate above 350 °C. The effect of impurities on the vacancy agglomerates disappeared in the defect recovery stage (≥350 °C).
Hydrogenated microcrystalline silicon (µc-Si:H) films of 10 nm thickness were prepared by the plasma-enhanced chemical vapor deposition method on glass substrates that had been coated by a layer composed of Si, O, and N. The chemical composition of this layer was changed systematically, and the resultant changes in the crystallinity of the µc-Si:H films were investigated using Raman scattering spectroscopy. We have found that SiN x layers inhibit nucleation of microcrystalline Si and the films deposited on them are dominated by an amorphous component, regardless of their stoichiometry. Substrate surfaces rich in Si-O bonds are preferable for the formation of high-quality µc-Si:H films. It has been also found that the morphology of the coated layers does not affect the crystallinity of the µc-Si:H films.
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