Pump‐probe studies of travelling coherent longitudinal acoustic phonon oscillations in GaAs

Abstract

AbstractWe report comprehensive studies of long‐lived oscillations in femtosecond optical pump‐probe measurements on GaAs based systems. The oscillations arise from a photo‐generated coherent longitudinal acoustic phonon wave at the sample surface, which subsequently travels from the surface into the GaAs substrate, thus providing information on the optical properties of the material as a function of time/depth. Wavelength‐dependent studies of the oscillations near the bandgap of GaAs indicate strong correlations to the optical properties of GaAs. We also use the coherent longitudinal acoustic phonon waves to probe a thin buried Ga0.1In0.9As layers non‐invasively. The observed phonon oscillations experience a reduction in amplitude and a phase change at wavelengths near the bandgap of the GaAs, when it passes through the thin GaxIn1‐xAs layer. The layer depth and thicknesses can be extracted from the oscillation responses. A model has been developed that satisfactorily characterizes the experimental results. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)