Vacancy-type defects in Mg-implanted GaN were probed using a monoenergetic positron beam. Mg ions of multiple energies (15-180 keV) were implanted to provide a 200-nmdeep box profile with Mg concentration of 4 Â 10 19 cm À3 . The major defect species of vacancies introduced by Mgimplantation was a complex between Ga-vacancy (V Ga ) and nitrogen vacancies (V N s). After annealing above 1000 8C, these defects started to agglomerate, and the major defect species became (V Ga ) 2 coupled with V N s. The defect reaction occurred between not only the defects introduced by the implantation but also the defects introduced by an excess Mg-doping. The depth distribution of vacancy-type defects agreed well with that of implanted Mg, and no large change in the distribution was observed up to 13008C annealing. Relationships between photoluminescence bands and vacancy-type defects introduced by Mg-implantation are also discussed.
Articles you may be interested inReuse of AIP Publishing content is subject to the terms at: https://publishing.aip.org/authors/rights-and-permissions. Phosphorus ions were implanted in ZnO single crystals with energies of 50-380 keV having total doses of 4.2ϫ 10 13 -4.2ϫ 10 15 cm −2 . Positron annihilation measurements reveal the introduction of vacancy clusters after implantation. These vacancy clusters grow to a larger size after annealing at a temperature of 600°C. Upon further annealing up to a temperature of 1100°C, the vacancy clusters gradually disappear. Raman-scattering measurements reveal the enhancement of the phonon mode at approximately 575 cm −1 after P + implantation, which is induced by the production of oxygen vacancies ͑V O ͒. These oxygen vacancies are annealed out up to a temperature of 700°C accompanying the agglomeration of vacancy clusters. The light emissions of ZnO are suppressed after implantation. This is due to the competing nonradiative recombination centers introduced by implantation. The recovery of the light emission occurs at temperatures above 600°C. The vacancy-type defects detected by positrons might be part of the nonradiative recombination centers. The Hall measurement indicates an n-type conductivity for the P + -implanted ZnO layer, suggesting that phosphorus is an amphoteric dopant.
Co-ITO granular magnetoresistance films fabricated by precipitation of magnetic nanoparticles from amorphous oxide J.A nanometer-scale hybrid film of Co particle/Co-C 60 compound was prepared by alternate deposition of Co and C 60 under UHV condition. All of Raman spectra, magnetization curves, and tunnel conductivity concluded that the hybrid system has a granular structure consisting of Co nanoparticles embedded in a Co-C 60 compound matrix. The magnetoresistance ratio of 26% was obtained at 2 K and 10 kOe for the electron tunneling across the Co-C 60 compound barrier. In addition, anomalously large bias voltage dependence was found in the magnetotransport properties.
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