Ion fractions of matrix elements and impurities in GaAs bombarded by O ⁺₂ primary ions

Summary

Useful ion yields Y of secondary ion mass spectrometry (SIMS) analyses were measured for GaAs bombarded with O ⁺₂ primary ions at normal incidence. The useful ion yields of several analytes were found to decrease with increasing ionisation potentialE _i of the analytes far less drastically than reported in the literature. For valuesE _i lower than ≈ 8 eV only a slight decrease of Y with increasing ionisation potential is observed. The saturation of the useful ion yields at lower values of the ionisation potential is interpreted to result from very high ion fractions. If an ion fraction of unity is assumed for Ga the ion fractions of impurities withE _i lower than 8 eV would exceed 40%. For analytes withE _i higher than 8 eV the ion fraction decreases rapidly with increasing ionisation potential. A value of 8×10⁻⁴ is estimated for the matrix element As (E _i= 9.81 eV).