RESUMEN
The dependences of the two-dimensional to three-dimensional growth (2D-3D) critical transition thickness on the composition for GeSiSn films with a fixed Ge content and Sn content from 0 to 16% at the growth temperature of 150 °Ð¡ have been obtained. The phase diagrams of the superstructure change during the epitaxial growth of Sn on Si and on Ge(100) have been built. Using the phase diagram data, it becomes possible to identify the Sn cover on the Si surface and to control the Sn segregation on the superstructure observed on the reflection high-energy electron diffraction (RHEED) pattern. The multilayer structures with the GeSiSn pseudomorphic layers and island array of a density up to 1.8 × 1012 cm-2 have been grown with the considering of the Sn segregation suppression by the decrease of GeSiSn and Si growth temperature. The double-domain (10 × 1) superstructure related to the presence of Sn on the surface was first observed in the multilayer periodic structures during Si growth on the GeSiSn layer. The periodical GeSiSn/Si structures demonstrated the photoluminescence in the range of 0.6-0.85 eV corresponding to the wavelength range of 1.45-2 µm. The calculation of the band diagram for the structure with the pseudomorphic Ge0.315Si0.65Sn0.035 layers allows assuming that photoluminescence peaks correspond to the interband transitions between the X valley in Si or the Δ4-valley in GeSiSn and the subband of heavy holes in the GeSiSn layer.
RESUMEN
Two-dimensional pseudomorphous Ge films have been grown to a critical thickness of 4 monolayers (ML) on Si(001). As a result of continuing deposition, pyramid-like Ge islands were grown in Stranski-Krastanov mode. The pyramid-like Ge islands deposited on Si(001) substrate using molecular beam epitaxy at 573 K reveal quantum dots (QDs) properties. The local microstructure parameters determined by EXAFS spectroscopy are linked to nanostructure morphology and adequate models are suggested and discussed. The pure Ge nanoclusters are covered by a 1-2 ML film with about 50% Si atom impurity caused by interface diffusion at 773 K. The influence of the effective thickness of the Ge film, Ge nanocluster sizes and Ge, Si deposition temperature on the QDs microstructure parameters is revealed. The first attempt to extract information about the energy structure of the free states of the quantum dot from X-ray absorption spectra (XANES spectra) was made. It was established that the maximum in the XANES spectra of a sample doped with boron is due to the appearance of free levels in the quantum dots at a depth of the order of 1.1 eV from the bottom of the Ge conduction band.