Lateral and cross-well transport of highly and moderately excited carriers in Si_1-xGe_x/Si superlattices

Picosecond transient reflectometry and dynamic grating techniques have been applied to investigate the perpendicular and parallel transport of optically excited carriers in strained-layer Si_0.83Ge_0.17/Si superlattices. We present results of the carrier ambipolar diffusivity and effective lifetime measurements in the layered structure and substrate within the 10¹⁷–10²⁰ cm^-3 density range. The combined experimental data are discussed in terms of parallel and perpendicular diffusion of carriers, interface recombination, and lattice heating. The estimated lateral and cross-well diffusion constants are 10 and 0.16 cm²/s at room temperature, respectively. © 1998 American Institute of Physics.