Characterization of light element impurities in gallium-nitride-phosphide by SIMS analysis

GaNP thin films grown by epitaxial processes show little or no carbon or oxygen incorporation when measured by secondary ion mass spectrometry. Accurate determination of impurity concentration is important for understanding the optical and electrical properties of this material. A new method for background subtraction is proposed, with the main assumption that the background contribution is inversely proportional to the secondary ion matrix signal. The total impurity concentration, i.e. the sum of real and background, is given by the inverse function. Efforts are taken to reduce background limits before background subtraction is performed. As the matrix signal increases, the background contribution becomes insignificant as the total impurity level approaches the real level. Multiple data points are obtained from several sputter rates. The real impurity level is obtained from the least-squares fit of the total impurity concentration versus matrix signal. Background subtraction via inverse function is an intuitive method that can be effectively used to remove gas-phase contributions in measurements of light elements in the thin films grown by epitaxial processes.