Effects of Lattice Relaxation on Composition and Morphology in Strained In x Ga1−x As y Sb1−y Epitaxial Layers
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In x Ga1−x As y Sb1−y is an important semiconductor material for a variety of mid-infrared devices. Its tunable bandgap, adjustable lattice constant, and other material properties make it appealing for developing optoelectronic devices in the 2 μm to 4 μm region. In this work, we report on the mechanisms of strain relaxation in In x Ga1−x As y Sb1−y epitaxial layers with low arsenic and high indium concentrations grown on GaSb (100) substrates. Samples were grown via solid-source molecular beam epitaxy with indium mole fractions between x = 0.1 (0.7% lattice mismatch) and x = 0.4 (2.5% lattice mismatch), and arsenic mole fractions between y = 0 and y = 0.02. Sample thicknesses between 10 nm and 100 nm were produced in order to observe the progression of structure formation. Samples were monitored in situ via reflection high-energy electron diffraction and ex situ using scanning electron microscopy, energy-dispersive spectroscopy, Rutherford backscattering spectroscopy, backscattering Raman spectroscopy, and atomic force microscopy. Results suggest that strain relaxation occurs preferentially along the  direction, although some crosshatching is observed. A compositional gradient in the growth direction is also observed, suggesting preferential incorporation of gallium at strained interfaces in order to minimize strain energy.
KeywordsInGaAsSb molecular beam epitaxy nanodashes compositional gradient strain relaxation
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The authors would like to thank Robert Bedford of the Wright–Patterson Air Force Base, Sensors Directorate for his contributions to this effort. The authors would also like to thank Suchismita Guha for allowing access to the micro-Raman spectrometer. This work was funded Air Force Office of Scientific Research Young Investigator Program Grant Number FA9550-10-1-0482.
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