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Lineshape and Lifetime Studies of Exciton Luminescence from Confined CuCl Thin Films

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Technical rept. 1988-1989

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Photoluminescence studies have been performed on structures, grown by molecular beam epitaxy, with thin films of Copper Chloride 30-1200A confined between layers of Calcium Fluoride. Excitons were formed by irradiation of these systems with UV frequencies above the CuCl bandgap, and the spectral and temporal dependences of the recombination radiation were compared to those of a bulk CuCl single crystal. We suggest a kinetic model to explain why the photoluminescence lineshapes of the free excitons in the films were characteristic of a much hotter exciton temperature and the radiative lifetimes were much shorter 40 ps than those of the bulk CuCl crystal. The photoluminescence from excitons created by hot electrons and holes that combine after above-bandgap excitation in confined CuCl thin films has been investigated. The lifetime of the free-exciton photoluminescence from films with thicknesses of 1200A and less was shorter than the 40-ps resolution of the instrumentation used, whereas the measured lifetime of that in a 1.5 microns- thick CuCl single crystal was 850 ps. This dramatic decrease of the lifetime has been attributed mainly to a decrease of the radiative lifetime of the excitons in the thin films. By examining the lineshape of the free-exciton photoluminescence, an effective temperature of the excitons at the time of decay could be determined. This temperature was increased both by decreasing the thickness of the region available to the excitons and increasing the exciton density.

Subject Categories:

  • Radiation and Nuclear Chemistry
  • Crystallography
  • Solid State Physics

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