Studies of carrier dynamics in epitaxial heterostructures by nonlinear optical and microwave techniques

We present nonlinear optical four-wave mixing (FWM) and microwave absorption (MWA) techniques for the monitoring of nonequilibrium carrier dynamics in CdTe epitaxial layers grown on GaAs by either hydrogen transport (H2T) or metalorganic vapour phase epitaxy, as well as in a sub-surface region of GaAs and CdTe single crystals. For the excitation, picosecond YAG or parametric laser pulses were used to record free carrier surface gratings with a variable thickness of the excited region, while ns-YAG pulses were utilized for the edge excitation of the heterostructures via a 3 mum diameter fiber. Fast transients of light diffraction allowed to determine the values of the diffusion coefficient, surface and bulk recombination velocities of the highly excited sample, and to study the ageing effect of MOVPE-grown epilayers. Asymptotic values of the carrier decay of about 2-4 mus were found in thick epilayers by MWA and attributed to a linear-recombination in thick CdTe epilayers grown by H2T-VPE.