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A characterization study of GaAs layers grown by metal-organic chemical vapour deposition (MOCVD) on silicon substrates is presented, based on high resolution transmission electron microscopy, secondary ion mass spectroscopy, admittance technique measurements (current-voltage, capacitance-voltage, capacitance and photocapacitance spectroscopy, deep level transient spectroscopy (DLTS) and photoluminescence (PL) spectroscopy in the near band gap and near infrared region). We have analysed the initial stage of growth and the influence of growth parameters as GaAs/AlAs superlattices (SLs) at different distances from the GaAsSi heterointerface in the buffer layer or post-growth thermal annealing or selective epitaxy on the reduction of dislocation density, on the silicon distribution, on the deep defect levels and on the coplanar tensile strain in the active layer. This study shows an improvement of the material quality in the dislocation density decrease due to GaAs/AlAs SLs grown directly on the initial prelayer, or post-growth annealing or selective epitaxy. DLTS measurements reveal deep electron traps in the range 0.5–0.7 eV below the CB induced by dislocations due to the heteroepitaxy. For the first time we observe deep hole centres in the range 0.4–0.5 eV above the top of the valence band, which could be involved in the reduction of the minority carrier lifetime. We discuss their origins due to silicon incorporation in the GaAs layer on the basis of capacitance and photoluminescence experiments. PL shows the increase of strain with post-growth annealing. Finally the improvement in the quality of the layers is pointed out on the basis of double heterostructure (GaAlAs/ GaAs/GaAlAs) characteristics.

High-quality fully strained ${\mathrm{Si}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Ge}}_{\mathit{x}}$ layers with 0%x22% grown on Si(100) by rapid thermal chemical vapor deposition have been analyzed by photoluminescence spectroscopy. We report a well-resolved near-band-gap excitonic transition observed in SiGe layers. These transitions make it possible to determine directly the fundamental band gap of such strained ${\mathrm{Si}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Ge}}_{\mathit{x}}$ alloys. The results show that high surface recombination in very thin films prevents the observation of radiative recombination, while demonstrating the striking effectiveness of a Si epitaxial capping layer in eliminating surface recombination.

At a low MBE growth temperature (400°C), an anisotropic composition modulation has been observed by Transmission Electron Microscopy (TEM) on AIlnAs layers. Optical measurements have been performed on these samples and compared with classical AllnAs grown at 530°C. We show the clustering “organization” on the low temperature layers and we propose some hypothesis to explain the composition modulation effects on the AlInAs optical properties.