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Two approaches have been compared for the low temperature epitaxy of thick, partially relaxed GeSn layers on top of Ge strain relaxed buffers. The benefit of using step-graded instead of constant composition layers when targeting really high Sn contents (16%, here) was conclusively demonstrated. Digermane (Ge2H6) and tin-tetrachloride (SnCl4) were used as Ge and Sn precursors, respectively. The growth pressure (100 Torr) and the F(Ge2H6)/F(SnCl4) mass-flow ratio being constant, it was through a temperature lowering that the Sn concentration in the graded structure was increased. X-ray diffraction, atomic force microscopy and transmission electron microscopy were used to gain access to the Sn concentration, the strain state, the surface morphology and thicknesses of the heterostructures. Using a step-graded approach allowed us to gradually relax the strain in the GeSn layers. It helped us obtain high crystalline quality and avoid Sn segregation/precipitation for high Sn contents. [ABSTRACT FROM AUTHOR]

One of the major challenges in the growth of vapor–liquid–solid (VLS) nanowires is the control of dopant incorporation in the structures. In this work, we study the n-type doping and morphology of nanowires grown by chemical vapor deposition when HCl is introduced. We obtain fully untapered nanowires with a growth temperature up to 410 °C and measure their resistivity using the 4-probe technique to be 2.0 mΩ cm. We perform energy dispersive x-ray measurements showing a concentration of dopants in the (5–7) × 1018 cm−3 range, being radially and axially uniform. The combination of these two measurements shows that the mobility is the same as for bulk germanium, demonstrating that the VLS mechanism has no detrimental effect for the electron transport in these nanowires. [ABSTRACT FROM AUTHOR]

Photoluminescence (PL) and time-resolved PL experiments as a function of the elaboration process are performed on Er-doped silicon-rich silicon oxide (SRO:Er) thin films grown under NH3 atmosphere. These PL measurements of the Er3+ emission at 1.54 um under non-resonant pumping with the Er f-f transitions are obtained for different Er3+ concentrations, ranging from 0.05 to 1.4 at.%, and various post-growth annealing temperatures of the layers. High resolution transmission electron microscopy (HRTEM) and energy-filtered TEM (EFTEM) analysis show a high density of Si nanostructures composed of amorphous and crystalline nanoclusters varying from 2.7 x 1018 to 1018 cm[?]3 as a function of the post-growth annealing temperature. Measurements of PL lifetime and effective Er excitation cross section for all the samples under non-resonant optical excitation with the Er3+ atomic energy levels show that the number of Er3+ ions sensitized by the silicon-rich matrix decreases as the annealing temperature is increased from 500 to 1050 degC. The origin of this effect is attributed to the reduction of the density of sensitizers for Er ions in the SRO matrix when the annealing temperature increases. Finally, extended x-ray absorption fine-structure spectroscopy (EXAFS) shows a strong correlation between the number of emitters and the mean local order around the erbium ions. [ABSTRACT FROM AUTHOR]