Dynamics of interstitial molecular-type double donor complexes in silicon

Abstract

Complementary time-resolved spectroscopies have been applied to study dynamics of molecular-type magnesium-related donors. Large interstate energy gaps of these donors prevent nonradiative decays through a first-order, one-phonon-assisted scattering – the main relaxation mechanism in shallow substitutional donors in low-doped silicon. Analysis reveals very short decay times of the deepest excited states of molecular donors: dephasing within less than 10 ps and relaxation rates above 30/ns. These decays are several times shorter than those observed in single-electron hydrogen-like substitutional donors, but longer than those in helium-like interstitial atomic magnesium centers in silicon. Spectral correlations of temporal dependences of particular transients to the lattice phonon overtones suggest that phonon-assisted electronic scattering contributes also to decoherence of states in these double donors. Such efficient second-order phonon-assisted processes were underestimated for dynamics of deep impurities in semiconductors.