SiGe Crystals Research Articles

Dislocation Kink Dynamics in Crystals with Deep Peierls Potential Relief

Institute of Solid State Physics, Russian Academy of Sciences, 142432 Chernogolovka,Moscow district, Russia(Received September 7, 1998)Processes of the nucleation and motion of kinks, determining the dislocation mobilities in crystalswith high Peierls barriers, are reviewed. Various mechanisms of an influence of point defects onthe kink dynamics are analyzed. To demonstrate these mechanisms experimental data are pre-sented obtained with two-level intermittent loading of Si, Ge, and bulk SiGe alloy single crystals.The instability of a dislocation glide in SiGe crystals has been discovered, and modes are revealedof the linear and nonlinear kink drift. The experimental data are analyzed in the framework ofmodels, considering the interaction of point defects with a dislocation and a kink.

Solid-phase crystallization of amorphous SiGe films deposited by LPCVD on SiO 2 and glass

The crystallization kinetics and film microstructure of poly-SiGe layers obtained by solid-phase crystallization (SPC) of amorphous SiGe with Ge fractions ( x) in the 0 to 0.42 range have been studied in detail. Amorphous SiGe layers 100 nm thick were deposited by LPCVD at 450°C on thermally oxidized Si wafers and 7059 Corning glasses, using Si 2H 6 and GeH 4 as gas sources. The samples were crystallized at 550°C and low pressure (below 9 Pa). The evolution of the crystallization and the resulting film microstructure were characterized by X-ray diffractometry and transmission electron microscopy. The experimental results on growth kinetics fit the Avrami’s model. The characteristic crystallization time decreases with x, slowly for x<0.3 and more abruptly for higher values of x. The transient time depends exponentially on x in all the intervals. The crystallized films have a (111) preferred orientation for low values of x and evolve to a randomly oriented polycrystal as x increases. The grain size in the fully crystallized layers decreases with increasing x. The results are similar for the films deposited on silicon dioxide and glass.

Dislocation Velocities and Mechanical Strength of Bulk GeSi Crystals

Dislocation Velocities and Mechanical Strength of Bulk GeSi Crystals

Dislocation Velocities and Mechanical Strength of Bulk GeSi Crystals

Dislocation Velocities and Mechanical Strength of Bulk GeSi Crystals

Formation of extended defects and strain relaxation in ion beam synthesised SiGe alloys

Single crystal SiGe alloy layers have been fabricated by implantation of Ge + ions at energies ranging from 70 to 400 keV, followed by Si + post-amorphisation and S olid P hase E pitaxial G rowth (SPEG). It is found that for each Ge + implantation energy a critical value of the peak germanium concentration exists above which extended defects nucleate in the vicinity of the peak of the germanium depth profile and extend up to the surface. A critical value of the elastic energy stored in the structures ( ∼300 mJ/ m 2 ) has been determined above which ion beam synthesised SiGe alloys relax, independently of the implantation energy. This empirical model has been found to successfully account for the results obtained in this work as well as in many other studies reported in the literature. For a regrowth temperature of 700°C, all samples investigated by XRD have been found to be almost fully strained, including samples containing relaxation-induced defects, indicating that, under these conditions, the energy transferred to the defects is very low. Complete strain relaxation is achieved after a second anneal step at 1000°C.

Fixed exit double-crystal monochromator with one single cooled crystal

The performance of a fixed exit double-crystal monochromator in terms of stability and reproducibility of the outgoing X-ray beam becomes the crucial point at modern synchrotron beamlines dealing with high-resolution X-ray optics. Due to the high heat load the monochromator crystals have to be cryogenically cooled. The cooling loop of the second crystal may have an impact on the performance of the monochromator. We therefore suggest to use a Si 1− x Ge x single crystal as the first cooled crystal of the monochromator. The second crystal is held at room temperature. To verify the proposed solution an experiment was performed where the lattice parameters of pure Si and SiGe crystals as a function of the temperature were measured.

Graded X-ray Optics for Synchrotron Radiation Applications.

Using X-ray diffractometry and spectral measurements, the structure and properties of graded X-ray optical elements have been examined. Experimental and theoretical data on X-ray supermirrors, which were prepared by the magnetron sputtering technique using precise thickness control, are reported. Measurements on graded aperiodic Si(1-x)Ge(x) single crystals, which were grown by the Czochralski technique, are also presented. The lattice parameter of such a crystal changes almost linearly with increasing Ge concentration. The measurements indicate that Si(1-x)Ge(x) crystals with concentrations up to 7 at.% Ge can be grown with a quality comparable to that of pure Si crystals.

Analysis of Si 1− xGe x on Si heterostructures grown by MBE as a function of substrate temperature

Si 0.8 Ge 0.2/Si (0 0 1) structures were grown at various growth temperatures (250–760°C) using MBE, and Si 1− x Ge x ( x=0.2, 0.35, 0.5) films (∼200 nm) were deposited on (0 0 1) Si substrate at room temperature using solid phase epitaxy (SPE) method and annealed subsequently at various temperatures (550–950°C). SiGe films with good single crystallinity were obtained from the samples grown at 440–660°C using MBE and dislocations were observed in the single crystal SiGe film for the samples grown above 680°C. For the sample annealed at 550°C for 30 min using SPE method, SiGe film was found to be amorphous. Single crystal SiGe film (∼30 nm) with defects was formed in the sample annealed at 650°C for 10 min, but amorphous SiGe layer still remained above the SiGe single crystal layer. For the sample annealed at above 750°C for 10 min all the amorphous SiGe was crystallized, but SiGe film was found to be polycrystalline.

Mechanical strength of GeSi solid solution

The mechanical strength of Ge 1 − x Si x . crystals with x ranging from 0 to 0.4 grown by the Czochralski method was investigated as functions of the composition and temperature by compressive deformation. The stress-strain curve of the GeSi alloys with a yield point phenomenon is similar to that of Ge and Si in the temperature range lower than about 600 °C. However, the yield stress of the alloys is temperature-insensitive at high temperatures and increases with increasing Si content in the range investigated. The composition dependence of the yield stress can be expressed by an x(1 −x) relation. The flow stress of GeSi crystals has an athermal component that is absent in Ge and Si and gives rise to solution hardening. The hardening mechanism in alloy semiconductors is discussed.

Dislocation and kink motion study in the bulk SiGe alloy single crystals

The individual dislocation mobility in bulk single SiGe crystals has been studied both with conventional and intermittent loading (IL) techniques. A model is used connecting the experimental data on dislocation paths with values of kink displacements under IL. The experimental data are compared with two models describing the interaction of a dislocation with point defects. It is shown that with small Ge concentration Cottrell atmosphere determines the dynamical drag of the dislocation giving rise to threshold immobilisation. With higher Ge content the specific mode of kink drift along the dislocation line (the motion in the field of random forces) takes place.

Bulk growth of silicon-germanium solid solutions

This paper provides an overview of the technology for growing bulk silicon-germanium solid solutions and of the structural properties of the solidified materials. It is an attempt to summarize and value the methods and efforts applied to the controlled crystallization of silicon-germanium melts which were employed during the last four decades. The especially high degree of segregation makes the system sensitive to small changes of growth conditions, which leads to inhomogeneities and strain. The future availability of homogeneous, low-defect Si-Ge crystals through the whole composition range is briefly discussed.

Cathodoluminescence from relaxed Ge xSi 1− x grown by heteroepitaxial lateral overgrowth

We present low temperature cathodoluminescence (CL) studies of relaxed Ge x Si 1− x , selectively grown on a patterned Si (111) substrate by liquid phase epitaxy, using heteroepitaxial lateral overgrowth. In the spectrally resolved CL of the resulting GeSi crystals, we observe an emission peak attributed to the recombination of free excitons (FEs). We further observe a peak of lower intensity at a lower energy position, caused by the unresolved phonon replicas of the FE peak. At an even lower energy position, we observe a comparatively broad luminescence band, attributed to CL from dislocations. Monochromatic images using the FE emission, or its phonon replica, reveal three types of contrast variations. On a 5 μm scale we observe dark line defects in the GeSi crystals, which we attribute to dislocations. In the lateral position of the seeding windows for the epitaxy, the GeSi crystals exhibit a dark, 20 μm wide band. On a 20 to 50 μm scale we observe small fluctuations in the Ge x Si 1− x composition, which manifests itself as local intensity variations with detection wavelength.

Bent-crystal monochromator for 150 keV synchrotron radiation

The 220 reflectivity curve of a 4 mm thick Si crystal is measured in asymmetric transmission (Laue) geometry. The crystal is bent to a radius varying from 24 to 138 m, and the analyzer is a nearly perfect Si(220) crystal in non-dispersive (+, −) arrangement. The full width at half-maximum of the reflectivity curves varies from 61 to 10 μrad, while that of a flat perfect crystal is 1.2 μrad, and the observed maximum reflectivity is about 60%. The calculated value is even higher, exceeding 80%. The bent crystal is used as an inverse-Cauchois monochromator, where the source of radiation is on the focusing circle. The effect of the beam divergence on the energy bandpass is eliminated, leaving only the contribution of the reflectivity curve. This can be matched to the desired resolution of the experiment by the choice of the thickness and asymmetry angle of the crystal. Compton-profile measurements from Ag and Au foils are used for a comparison of different monochromators. The bent-crystal monochromator provides 50 times more flux than the perfect Si(220) crystal and a better energy resolution than heat-treated Si(220) or mosaic Ge(220) crystals.

13. Measurement of the lattice constant of SiGe heteroepitaxial layers grown on a silicon substrate

The lattice constant of thin heteroepitaxial layers composed of single crystal SiGe solid solutions various compositions grown on silicon substracts were measured. The measurements were performed by X-ray diffraction method. The fact that the layers are thin and, therefore, there is also reflection from the silicon substrate (in addition to the reflection from the layer) is utilized for this measurement method. A review of the measurement method is given and the experimental results obtained by irradiating the samples with CuK α are presented. Specific problems related to the measurement methods and to the layer lattice structure are also presented. There are: resolution problems between the reflections from the layer and the substrate for low Ge concentrations, deformation problems, the effects of the defects and non-uniform changes in the lattice constant at different crystallographic orientations.