Nuclear microanalysis of oxygen concentration in liquid-phase epitaxial gallium phosphide

Abstract

The total bulk oxygen concentration has been determined in GaP layers grown by liquid-phase epitaxy. Layers were grown doped with 18O enriched oxygen, and the 18O concentrations were measured by detecting α particles emitted during proton irradiation using the nuclear reaction 18O(p, a)15N. The relative concentrations of 18O and 16O were determined from exciton luminescence of the LiI–LiGa–OP complex at 4.2°K after Li diffusion, thus enabling the total bulk oxygen concentrations to be determined. The total solid solubility of oxygen in GaP containing the optimum zinc concentration for efficient luminescence from Zn-O nearest-neighbor pairs, 5 × 1017 cm−3, ranged from [sine wave] 5 × 1016 cm−3 at [sine wave] 1040°C to [sine wave] 9 × 1016 cm−3 at ≳1100°C. Measurements on a layer doped with tellurium and oxygen failed to detect any 18O, indicating that the total oxygen concentration was probably < 4 × 1016 cm−3. The experimental results confirmed the presence of Ga2O3 coprecipitates when the oxygen added to the liquid phase was greater than the solubility. Channeling experiments to determine the oxygen site location were done, but the results were inconclusive. The methods of crystal preparation and 18O doping are described, and the techniques employed to prevent oxygen isotope exchange are discussed. Other experimental techniques which are described include a large solid angle α-particle detector arrangement which also allowed sample orientation, a graded thickness foil which stopped backscattered protons and preserved the α-particle resolution, and the methods for minimizing and correcting for boron background which occurs through the reaction 11B(p, α)8Be*.