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

Abstract

Useful ion yields Y of secondary ion mass spectrometry (SIMS) analyses were measured for GaAs bombarded with O2+ primary ions at normal incidence. The useful ion yields of several analytes were found to decrease with increasing ionisation potentialEi of the analytes far less drastically than reported in the literature. For valuesEi 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 withEi lower than 8 eV would exceed 40%. For analytes withEi 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 (Ei= 9.81 eV).