Detection of semiconductor dopants using accelerator mass spectrometry

We have used the tandem accelerator mass spectrometer at the University of Arizona to detect dopants and other impurities in Si and GaAs. B, P, As and Sb doped Si crystals have been examined, with detection limits ranging from ~ 0.5 ppb (parts-per-billion) for B to ~10 ppb for P and Sb. B and Cr doped GaAs have also been examined, with detection limits of ~ 0.5 and 40 ppb, respectively. The terminal voltage for these experiments was 1.8 MV, and a post-acceleration carbon stripper foil ( ~ 350 Å) was used to lower the magnetic rigidity of heavy ions before entering the analyzing magnets.