Interpretation of "optical time-of-flight" measurements in Si.

Abstract

The optical time-of-flight (TOF) technique developed by Forchel, Hillmer, and co-workers for investigation of carrier transport in Si is examined. The TOF method detects the arrival of electron-hole pairs at the surface of a thin slab following their creation by pulsed laser excitation of the opposite surface. At high excitation levels, the optical TOF data were interpreted as evidence for rapid drift motion of electron-hole plasma at several times the sound velocity. At low excitation levels, the optical TOF results have been interpreted in terms of diffusive transport of excitons, surface recombination, and in some analyses, macroscopic drift. We show that both the high- and low-excitation cases are consistent with a very simple model that includes only classical diffusion and surface recombination. In particular, supersonic plasma drift is not required to explain the optical TOF results.