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We analyze the linewidth of intersubband absorption features observed in n-type s-Ge/Ge0.82Si0.18 multiquantum wells grown on Si(001) substrates. Supported by a thorough theoretical modeling, we discuss the role on the line broadening of electron scattering due to interface roughness, spatial distribution and density of ionized donors, phonons, alloy disorder, and extended defects. To this aim, the absorption spectra of a set of samples featuring different well widths and doping profiles are measured obtaining a very good agreement with the theoretical results. We demonstrate values of the half width at half maximum of the E0->E1 absorption peak as small as 2 meV. Our analysis suggests that the coherence time of electron wave functions in n-doped Ge/SiGe quantum wells is not yet limited by intrinsic scattering mechanisms up to room temperature, opening new perspectives for the quantum design of silicon-based light emitting devices.

In this paper, we have experimentally and numerically studied the nonradiative intersubband (ISB) relaxation in $n$-type Ge/SiGe quantum well (QW) systems. Relaxation times have been probed by means of pump-probe experiments. An energy balance model has been used to interpret the experimental differential transmission spectra and to assess the relevance in the nonradiative relaxation dynamics of both electron and lattice temperature as well as of the carrier density. The comparison between experimental data and theoretical simulation allowed us to calibrate the interaction parameters which describe the electron-optical phonon scattering in two-dimensional (2D) Ge systems. Characteristic relaxation times has been calculated and compared with those of GaAs QWs as a function of the 2D electron density, of the subband energy separation, and of the lattice and electronic temperature. We found that ISB relaxation times for the Ge/SiGe systems are generally shorter than that previously calculated when the electron distribution was neglected. Nonetheless, our main result is that the relaxation time in Ge/SiGe QW systems is longer than 10 ps, also for transition energies above the Ge optical phonon energy, up to 300 K. Furthermore, we obtained that the relaxation times are at least one order of magnitude longer than in GaAs-based systems.

""\\"We present a synergic experimental and theoretical investigation of the plastic relaxation onset in low-temperature Ge growth on Si(001). High-resolution transmission electron microscopy reveals that misfit is released by pairs of coupled 60° dislocations. Atomic resolution proved to be key in distinguishing pairs from single 90°dislocations because of the revealed small intra-pair dislocation distance (even less than 1 nm). By exploiting dislocation theory and molecular dynamics simulations, we demonstrate that the observed pairing naturally occurs as a result of the mutual interactions between the two dislocations. In particular, analytical models show that the stress field arising in a thin film when a dislocation segment lies at the interface with the substrate determines the most favored nucleation site for a new (complementary) dislocation that leads, after migration, to the coupling with the first in a stable position. At the growth temperature, further motion or recombination due to atomic scale effects is excluded by classical molecular dynamics simulations. A clear picture of the early stages in the strain relaxation emerges, gliding out of the interface and\\\\\\\/or short-range climbing (as typically produced by annealing or higher temperature steps, but not taking place under the present growth conditions) being required to transform pairs into a single edge dislocations. The present results also offer answers to the long-held puzzling question about the mechanism originating 90° dislocation in high mismatch Ge\\\\\\\/Si systems. \\"""

""We report on the experimental and theoretical investigation of the relaxation in Ge-rich SiGe\\\/Ge\\\/Si heterostructures. The experimental x-ray diffraction data are interpreted with the help of a model including both edge and 60 degrees misfit dislocations in the calculated x-ray scattering intensity. Our results show that highly positionally correlated edge dislocations dominate in the relaxation of the compressive strain at the Ge\\\/Si interface, while a smaller tensile strain at the SiGe\\\/Ge interfaces released by uncorrelated\\\/little correlated 60 degrees dislocations.""