Si 0.7 Ge 0.3 epilayers with low threading dislocation density have been grown on Si (001) substrates by introducing a low temperature Si buffer. Such a structure can be used as the buffer for the growth of device structures. In comparison with the conventional compositionally graded buffer system, it has the advantages of having lower threading dislocation density, smaller thickness for required degree of relaxation, and smoother surface. Experimental evidence suggests that an anomalous relaxation mechanism has been involved.
Relaxed GexSi1−x epilayers with high Ge fractions but low threading dislocation densities have been successfully grown on Si (001) substrate by employing a stepped-up strategy and a set of low-temperature GeySi1−y buffers. We show that even if the Ge fraction rises up to 90%, the threading dislocation density can be kept lower than 5×106 cm−2 in the top layers, while the total thickness of the structure is no more than 1.7 μm.
A model has been developed to describe x-ray scattering from CuPt-type ordered III-V ternary semiconductor alloys. The model takes into account the size distribution of the two different laminae-shaped variants, the random distribution of antiphase domain boundaries in each variant, and the atomic displacements due to the bond-length difference between the two constitutive binary materials. A synchrotron x-ray source was employed to measure the weak-ordering reflections from CuPt-ordered Ga 0.5 In 0.5 P and Al 0.5 In 0.5 As samples. By comparing the experimental results and the model calculations, structure information, including the average number of atomic layers in the laminae of each variant, the average antiphase domain size, and the average order parameter in each variant, were obtained. Results from single-variant films and poorly ordered films are also discussed.
A quantitative structural model, based on x-ray diffraction, is provided to analyze quadruple-period atomic ordering along ͓110͔ in a GaAs 0.87 Sb 0.13 alloy grown on a ͑001͒ GaAs substrate by molecular beam epitaxy. To minimize the local strain energy derived by a valence force field ͑VFF͒ model for the alloy, atomic displacements were deduced and incorporated in our model. Calculation of the scattering pattern based on the model agrees well with experiment. We propose that this ordering originates from a (2ϫ4) surface reconstruction and the difference in properties of the atomic species.
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