Femtosecond photomodulation spectroscopy of a-Si:H and a-Si:Ge:H alloys in the midinfrared

J. A. Moon, J. Tauc, J. K. Lee, E. A. Schiff, P. Wickboldt, W. Paul

Research output: Contribution to journalArticlepeer-review

17 Scopus citations


We present the results of a low-intensity femtosecond pump and probe study of hydrogenated amorphous silicon (a-Si:H) and its germanium alloys (a-Si:Ge:H) in the probe spectral regions of 0.52-0.81 and 1.19-1.48 eV. We find that the picosecond photoinduced change in the energy and time dependence of the complex dielectric constant is consistent with a model for the injected carrier relaxation which combines extended-to-tail and tail-to-tail thermal carrier transitions, and which uses an optical probe sensitivity to carriers in the localized tail states. The measurements on a-Si:H are in quantitative agreement with our model over the entire probe spectral range and from subpicosecond to nanosecond probe delay times; however, we find only qualitative agreement between the model and the pump-probe results of two series of a-Si:Ge:H alloys prepared under different conditions. Fits to the subpicosecond data of both the a-Si:H and a-Si:Ge:H samples indicate that the carriers are initially trapped into the tail states with a characteristic attempt frequency at least eight times higher than the rate at which they are subsequently trapped into deeper tail states.

Original languageEnglish (US)
Pages (from-to)10608-10618
Number of pages11
JournalPhysical Review B
Issue number15
StatePublished - 1994

ASJC Scopus subject areas

  • Condensed Matter Physics


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