Photoemission Study of Donor Impurities in Semiconductors

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They will study donor impurity levels in semiconductors by photoemission spectroscopy. Concentrations as low as one part in 10-6 will be studied with meV energy resolution, at a photon energy near 5 eV. Many systems will be studied. The Silicon:Phosphorus system is emphasized. One set of experiments will use the surface sensitivity of the photoemission technique to study impurity levels near surfaces. The large effective hydrogenic radius of 20 A for Phosphorus and Silicon should result in a significantly defferent binding energy of the Phosphorus levels near the surface than in the bulk. This study will produce the first experimental observation of this surface binding enrgy shift. A second set of experiments will exploit the unique power of photoemission spectroscopy to directly observe the one electron density of occupied levels and study impurity band formation as a function of concentration. The concentration range near the metal/insulator critical concentration (3x10-18/cm3 for Silicon:Phosphorus) will be emphasized. This study will show the electronic density of states directly, and determine the bandwidth and Fermi level position as functions of concentration.