Abstract

The transport properties of photoexcited carriers in the extended states of a-Si:H has been controversially discussed in the past twenty years. However, it is widely accepted that the energy relaxation within extended states and initial trapping into bandtail states occur on a subpicosecond timescale. It is difficult, therefore, to extract transport data of free carriers directly from steady state electrical or optical methods. These difficulties can be overcome using optical pump/probe techniques with subpicosecond time resolution. We measure photoinduced changes of the dielectric function in a pump/probe transmission and reflectance experiment on a 0.5 µm thick a-Si:H film, using 50 fs laserpulses at 2eV for excitation and 100fs-broadband continuum pulses (1.3 eV- 1.9eV) for probing.

© 1992 IQEC