CHARACTERIZATION OF IMPURITIES IN II-VI SEMICONDUCTORS BY TIME-RESOLVED LINESHAPE ANALYSIS OF DONOR-ACCEPTOR PAIR SPECTRA

Strength and energy position of donor-acceptor pair (DAP) luminescence bands are often used for a crude estimate of impurity incorporation and nature in II-VI epilayer structures. We demonstrate that analysis of DAP emission has to be performed more carefully to get reliable information of that kind. A thorough lineshape analysis allows one to determine the acceptor binding energy quite exactly if the donor energy is known, and beyond this the phonon-coupling parameters. A missing or reduced line narrowing of the DAP bands in thin epilayers for decreasing excitation densities is due to inhomogeneous impurity distribution within the strain-profiled layers. In ns time-resolved analysis, DAP decay is shown to depend sensitively on detection energy within the band but is, at all energies, perfectly described by biexponential fits. Fit parameters involve impurity binding energies and, thus, are an independent tool of verifying data obtained from lineshape analysis. Spectrally unresolved double bands can be identified and distinguished by this method.