Quantum-confined Franz-Keldysh effect in CdTe quantum dots in glass

There has been considerable interest in the electric-field dependence of optical properties of semiconductor quantum-well structures. We have extended these electric-field studies to quantum dots, i.e., to structures confined in all three dimensions. The new CdTe quantum-dot glass first reported here is especially suited for electric-field effects because of the large Bohr radius, aB = 73 Å; it has as many as six quantum-confinement peaks in the absorption spectrum with dot radii, ro = 36 Å. The observed changes in the absorption spectrum (see top figure) are interpreted to arise mainly from a red shift of the lowest transition and the redistribution of the oscillator strength as forbidden transitions are opened up by the symmetry-breaking action of the external field. This interpretation is made plausible by a spherical-coordinate-system calculation (upper figure), that neglects the Coulomb interaction; it is similar to that for cuboidal structures by Miller, Chemla, and Schmitt-Rink, and predicts a differential absorption spectrum in good qualitative agreement with the data.

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