Abstract

A method is described for determining small concentrations of oxygen in single crystals of gallium phosphide; 14-MeV 3He particles were used to convert 16O into 18F, which was then separated from other radioactive nuclides produced by bombardment of gallium. Coincidence counting of γ-pairs produced by annihilation of emitted positrons was then used. Thin surface layers were removed from the crystals after irradiation to avoid interference from surface contamination and from recoiled oxygen nuclei driven into the lattice during bombardment. Results are reproducible and appear to be accurate to within 20%. Observed oxygen levels in gallium phosphide single crystals varied from about 5·10 17 atoms cm −3 in specimens prepared by solution growth or halogen transport, to about 5·10 18 atoms cm −3 in specimens prepared by wet hydrogen transport, 2·lO -19 atoms cm −3 in oxygen-doped solution-grown crystals.

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