F. Sette

Ion implantation in GaAs

Recent advances in the understanding of the relationship between implanted dopant solubility and electrical activity in GaAs are reviewed and direct lattice configuration measurements explaining these results are presented. The nature of residual defects remaining after activation annealing of GaAs, in particular rapid thermal annealing, are discussed, along with a review of the application of ion beams in promoting compositional disordering of GaAs-AlAs superlattices. The outstanding problems remaining in the use of ion implantation technology for GaAs are also detailed.

High Resolution Soft X-Ray Spectroscopies with the Dragon Beamline

Novel spectral features and new information regarding core-excitation processes are revealed in the photoabsorption and photoemission experiments performed with a newly constructed synchrotron radiation beamline. This beamline, dubbed Dragon, has an unprecendented resolving power and superior transmission in the soft x-ray region. Several experimental results on gas phase, solid and biological systems are presented to exemplify the scientific applications of high resolution soft x-ray spectrocopies. The possible application of photoabsorption spectroscopy as a tool for chemical analysis is also discussed and a few examples are given.

Local structure of S impurities in implanted GaAs

The local structure of S implanted at high doses (10 15 −10 16 cm −2 , 100 keV) into GaAs and annealed at 900°C has been determined by extended X-Ray absorption fine structure by monitoring the S (K α ) fluorescence yield. The S first neighbor shell shows a significant static broadening compared to the S second and third shells. This indicates two S configurations of approximately equal population: (1) substitutional S on an As site and (2) a complex formed by S on an As site and an As vacancy on the second shell with a S-first neighbor distance relaxation of 0.14 ± 0.04 A. The two-site configuration explains the well-known disparity between implanted S concentration and net electrical activity, a phenomenon which occurs at high concentrations for all donor species implanted in GaAs.

Extended X-ray Absorption Fine Structure Studies by Soft X-ray Fluorescence Detection

Comparison of x-ray fluorescence and electron-yield surface extended x-ray absorption fine struction (EXAFS) above the S K-edge for c(2 × 2)S on Ni(100) reveals an order of magnitude higher sensitivity for the former technique due to a much lower background. The higher sensitivity of soft x-ray fluorescence EXAFS opens the possibility of structural studies on very dilute atomic species on surfaces (< 0.1 monolayer) or in the bulk (< 1019 atoms/cm3) of a different material. An EXAFS study on the local structure of S impurities in GaAs is presented as an example of such studies. We derive the local geometry around the S atoms finding two competing configurations of approximately equal population: (1) substitutional S on an As site (2) a complex formed by S on an As site and an As vacancy on the second shell with a S-first neighbor distance relaxation of 0.14 ± 0.04 A. The two configurations explain the disparity between implanted S concentration and net electrical activity.