Measurement of the diffusion coefficient and recombination effects in germanium by diffraction from optically-induced picosecond transient gratings

A variation of the excite‐and‐probe technique is used to measure the picosecond evolution of laser‐induced transient gratings that are produced in germanium by the direct absorption of 35‐psec optical pulses at 1.06 μm. Grating lifetimes are determined as a function of grating spacing and sample temperature for peak carrier densities of approximately 5×1019 cm−3. A linear diffusion‐recombination model for the grating decay provides a good fit to the experimental data and allows the extraction of the diffusion coefficient and places limits on the recombination lifetime.