Effect of size dispersion on the optical absorption of an ensemble of semiconductor quantum dots

The linear optical absorption of an ensemble of semiconductor quantum dots randomly positioned in an insulating matrix is studied theoretically and ex perimentally for the CdTe/glass system. The calculation of the effective di electric function of the system, whose imaginary part determines the absorp tion, is based on a modified Maxwell-Garnett formalism using a diagram tech nique to calculate the average renormalized polarizability of spherical qua ntum dots. This approach takes into account both the fluctuations of the po larization interaction due to the random positions of the spheres and their size dispersion. A comparison of the theoretical and experimental spectra permits determination of the mean quantum dot size and concentration. The d ependence of these parameters on the postgrowth annealing time of the sampl es is not consistent with the existing theories on the spinodal decompositi on of solid solutions. (C) 1998 American Institute of Physics. [S1063-7826( 98)01711-6].