Browsing by Author "Crouch, Roger Keith"

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    A study of beryllium and beryllium-lithium complexes in single-crystal silicon
    Crouch, Roger Keith (Virginia Polytechnic Institute and State University, 1971)
    When beryllium is thermally diffused into silicon, it gives rise to acceptor levels 191 meV and 145 meV above the valence band. Quenching and annealing studies indicate that the 145 meV level is due to a more complex beryllium configuration than the 191 meV level. When lithium is thermally diffused into a beryllium doped silicon sample it produces two new acceptor levels at 106 meV and 81 meV. Quenching and annealing studies indicate that these new levels are due to lithium forming a complex with the defects responsible for the 191 meV and 145 meV beryllium levels, respectively. Electrical measurements imply that the lithium impurity ions are physically close to the beryllium impurity atoms. The ground state of the 106 meV beryllium-lithium level is split into two levels, presumably by internal strains. Tentative models are proposed to explain these results.
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    Thermal ionization energy of lithium and lithium-oxygen complexes in single-crystal silicon
    Crouch, Roger Keith (Virginia Polytechnic Institute, 1967)
    The ionization energy of lithium as an impurity in single-crystal silicon has recently been determined by optical means to be dependent upon the amount of oxygen in the silicon. It was found that for float-zone crystals, having a relatively low oxygen content (less than 10¹⁶ cm⁻³), the ionization energy was about 32 meV, whereas for a pulled-crucible crystal, having a higher oxygen concentration (approximately 10¹⁸ cm⁻³), the ionization energy was 39 meV. Previous measurements by means of Hall effect studies had indicated that the ionization energy in a pulled crucible sample was about 33 meV which seemed to agree with the optical float-zone value. In an attempt to clarify the situation, Hall effect measurements were made on pulled-crucible and float-zone silicon samples containing lithium as an impurity, and ionization energies were calculated. It was found that this new Hall effect data seemed to show the same dependency on oxygen content as the optical data had shown with the ionization energy, being 37 meV for the pulled crucible sample and 29.5 meV for the float-zone