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Articles you may be interested inInvestigation of high hole mobility In0.41Ga0.59Sb/Al0.91Ga0.09Sb quantum well structures grown by molecular beam epitaxy Appl. Phys. Lett.Strain relief and AlSb buffer layer morphology in GaSb heteroepitaxial films grown on Si as revealed by highangle annular dark-field scanning transmission electron microscopy Appl. Phys. Lett. 98, 082113 (2011);The real-time stress evolution has been investigated during molecular-beam epitaxial growth of GaAs 1−x Sb x / GaAs metamorphic buffer. These real-time data were obtained using an in situ multibeam optical sensor measurement and has been combined with detailed analysis of data obtained from x-ray diffraction, transmission electron microscopy, and atomic force microscopy. We compare the strain relaxation of two different compositions of GaAs 1−x Sb x , and correlated the development of dislocation structure and morphology. Several distinct stages of the strain relaxation were observed during growth, which can be separated in three main regimes: pseudomorphic growth, fast strain relaxation, and saturation. Transmission electron microscopy data show that GaAs 0.5 Sb 0.5 buffer layers have a larger fraction of pure-edge dislocations that arise during the earliest stages of growth. This could have a significant influence in the fabrication of buffer layers, since pure edges are favored over the threading dislocations. The strain relaxation profile for each film was modeled using a modified model of Dodson and Tsao ͓Phys. Rev. B 38, 12383 ͑1988͔͒ that takes into account the elastic interactions of misfit dislocations. The model results agree with the experimental data and show that interaction of misfit dislocations is responsible for the large residual stress. In addition, following the description developed by Dodson and Tsao ͓Phys. Rev. B 38, 12383 ͑1988͔͒ for the rate of dislocation multiplication, we were able to determine the line density of threading dislocations from the experimental data. This has a potential application in the design of metamorphic buffer layers because our observations are made in real time on individual growth, without the need of external characterization to measure the dislocation density.

Epitaxial heterostructures constitute a wide variety of modern microelectronics devices. In the limit of ever decreasing feature dimensions, now entering the nanoscale in some cases, the interfaces of such devices are crucial to their operation and performance. In general the properties of the interfaces will differ significantly from those of the bulk structure of either the substrate or the heteroepitaxial film. To date, direct, non-destructive characterizations of the atomic-level structure of films and interfaces have not been readily available and this has hampered the design and optimization of heteroepitaxial devices. We describe here a novel x-ray interference method which is useful for imaging such structures with sub-Ångstrom spatial resolution while also providing chemical composition information from a map of the electron density. We illustrate the method, known as Coherent Bragg Rod Analysis (COBRA), with recent results on GaSb-InAs heterostructures of interest as infrared sources and detectors. We show that, with detailed knowledge of the interfaces from COBRA, it is now feasible to correlate specific molecular beam epitaxy growth conditions with desired electronic characteristics associated with the interface bonding. The COBRA method is quite general and only requires an epitaxial relationship between the substrate and the nanostructure that is deposited on it.