M. A. Revenko

Plastic relaxation of solid GeSi solutions grown by molecular-beam epitaxy on the low temperature Si(100) buffer layer

The role of a low temperature Si buffer layer (LT-Si) in the process of plastic relaxation of molecular-beam epitaxy grown GeSi/Si(001) is studied. Probable sources and mechanisms of generation of misfit dislocations (MD) are discussed. Transmission electron microscopic and x-ray diffraction techniques are used for studying 100 nm GexSi1−x films with LT-Si and those free of such a buffer layer. The MD density is found to be much lower in the former than in the latter, and the level of the film plastic relaxation is not higher than 20% in both as-grown and annealed films with LT-Si. As the thickness of the solid solution layer reaches 300-400 nm, the plastic relaxation of the films increases to almost 100%. Therefore, the determining role of the MD multiplication is supposed. We assume the double role of the LT-Si buffer layer. First, the diffusion flux of vacancies from the LT-Si layer to the GeSi/Si interface may cause erosion of the interface and, as a result, a decrease in the rate of MD generation at ...

Direct observations of dislocation half-loops inserted from the surface of the gesi heteroepitaxial film

The initial stage of relaxation of mechanical stresses in the Ge0.32Si0.68∕Si(001) heterostructure grown by low-temperature (300°C) molecular-beam epitaxy is studied by means of transmission electron microscopy. Dislocation half-loops propagating from the film surface and generating misfit dislocations during expansion are visualized.

Strain relaxation of GeSi/Si(001) heterostructures grown by low-temperature molecular-beam epitaxy

Plastic relaxation in GexSi1−x∕Si(001) heterostructures with x=0.18–0.62, grown at temperatures of 300–600 °C with the use of a low-temperature (350 °C) Si buffer layer, is considered. It is shown that the use of low-temperature Si and low temperature of growth of GeSi films decreases the density of threading dislocations to the value of 105–106cm−2 in heterostructures with a germanium content x<¯0.3, whereas the density of the threading dislocations in heterostructures with a higher content of Ge remains at the level of ∼108cm−2 and higher. By means of transmission electron microscopy, it is shown that the origination of dislocation half-loops from the surface in the case of a high content of germanium in the film is the main reason for the high density of threading dislocations. Growing of GeSi films with a two-step change in composition is considered. The fact that the density of the threading dislocations in the first step of the film is significantly higher than that in the substrate is noted. Becaus...

Solid solutions GeSi grown by MBE on a low temperature Si (001) buffer layer: specific features of plastic relaxation

Abstract The role of a low temperature Si buffer layer (LT-Si) in the process of plastic relaxation of MBE grown GeSi/Si (001) is studied. Probable sources and mechanisms of a generation of misfit dislocations (MD) are discussed. Transmission electron microscopic and X-ray diffraction techniques are used for studying 100 nm GexSi1−x films with LT-Si and those free of such a buffer layer. The MD density is found to be much lower in the former than in the latter and the level of the film plastic relaxation is not higher than 20% in both as-grown and annealed films with LT-Si. As the thickness of the solid solution layer reaches 400 nm, the plastic relaxation of the films increases to almost 100%. Therefore, the determining role of the MD multiplication is supposed. We assume the double role of the LT-Si buffer layer. Firstly, the diffusion flux of vacancies from the LT-Si layer to the GeSi/Si interface may cause erosion of the interface and as a result a decrease in the rate of MD generation at the early stages of epitaxy. Secondly, the generation of intrinsic defect clusters in the LT-Si, which are potential sources of MDs, occurs in the field of mechanical stresses of the growing pseudomorphic layer. This process is thought to be the key feature of plastic relaxation of GeSi/LT-Si/Si (100) films which promotes MD self-organization.

Enhanced strain relaxation in a two-step process of GexSi1−x/Si(001) heterostructures grown by low-temperature molecular-beam epitaxy

Two-layer GexSi1−x heterostructures, with a finite fraction of germanium up to x=0.48 and a thickness of at most 0.65 μm, were grown by molecular-beam epitaxy. It is shown that plastic relaxation of the second step is significantly enhanced. It is assumed that threading dislocations with a density of 105–106 cm−2, which appear in the first step in the process of its plastic relaxation, are sources of misfit dislocations positioned between the first and second steps. Cross-sectional transmission electron microscopy showed the superior quality of the dislocation network in the stepped regions. Threading dislocation densities in the second step were determined with the help of etching pits and were found to be close to 105 cm−2.

Origination of misfit dislocations at the surface during the growth of GeSi/Si(001) films by low-temperature (300–400°C) molecular-beam epitaxy

The method of the molecular-beam epitaxy, at comparatively low temperatures (300–400°C), was used to grow GexSi1 − x/Si(001) films with a constant composition (x = 0.19–0.32) across a film and as well as two-layer heterostructures with the Ge content at the upper layer no lower than 0.41. Using transmission electron microscopy, it is shown that the main cause of an increase in the density of threading dislocations with increasing Ge fraction in the plastically relaxed films is the origination of the dislocation half-loops at the film surface; in turn, these dislocation half-loops are generated owing to the formation of a three-dimensional profile at the surface of the growing or annealed film.

InP decomposition phosphorus beam source for MBE: design, properties and superlattice growth

The use of GaP and InP crystal decomposition for generating phosphorus molecular beam in MBE growth of multicomponent III-V alloys and multilayer heterostructures involving phosphorus is analysed. The operating characteristics of an InP decomposition phosphorus beam source are presented and MBE growth of InGaP and InGaAsP alloys with controlled composition in both sublattices is described. The usefulness of the source is further demonstrated by growing InGaP/InGaAsP short-period (8 nm) superlattices with high structural perfection as revealed by x-ray diffraction and transmission electron microscopy studies.

Shifts and splitting of energy bands in elastically strained InGaP/GaAs(111)B epitaxial films

Strain-induced shifts and splitting of energy bands are studied by optical techniques in compressively strained pseudomorphic InxGa1−xP films grown by liquid phase epitaxy on lattice-mismatched GaAs(111)B substrates. The elastic strains are measured by the x-ray diffraction technique and reach the value of 0.92%. The splitting of the valence band is revealed as a doublet in the derivative of a photocurrent spectrum which is precisely measured on the semiconductor-electrolyte interface near the fundamental absorption edge. The maximum splitting reaches 45 meV. The sublinear behavior of the valence band splitting versus elastic strain is clearly observed. This nonlinearity is explained by the interaction between the strain-split subband with J=3/2, mJ=±1/2 and the spin-orbit split subband (J=1/2, mJ=±1/2). The experimentally measured dependences of shifts and splitting on the magnitude of strain are well described by the theoretical calculations.

Shear deformation potential of elastically strained InGaP/GaAs(111)B and InGaAsP/GaAs(111)B films

Elastically compressed InGaAsP epilayers were grown in a wide interval of compositions (with bandgaps from 1.4 to 1.9 eV) on GaAs(111)B substrates by liquid phase epitaxy. The splitting of the valence band was found by taking the derivative of photocurrent spectra. Its value was as high as meV for narrow-bandgap epilayers ( eV) and eV for wide-bandgap epilayers ( eV). The calculated shear deformation potential, d, was found to be eV for narrow-bandgap and eV for wide-bandgap films. A nonlinear dependence of the valence-band splitting on elastic strain was clearly observed for the wide-bandgap epilayers. This nonlinearity was explained by taking into account the interaction of the light-hole band with the spin - orbit-split valence band.

Liquid phase epitaxy of highly strained InGaAsP/GaAs films in the 1.4-1.8 eV interval of band gaps

Abstract Highly elastically strained films of InGaAsP solid solutions in the 1.4–1.8 eV interval of band gaps were grown on GaAs(1 1 1)B substrates by liquid phase epitaxy (LPE) for the first time. Elastic strains close to 1% are reached. The determined critical thicknesses exceed the predictions of the energy equilibrium theory by Matthews and Blakeslee by as much as an order of magnitude. Up to this date these data are record results for LPE technology of superthin films and for the InGaAsP/GaAs quaternary films for all technologies.