Optical and Structural Properties of InAs/GaSb Nanostructures
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Optical and Structural Properties of InAs/GaSb Nanostructures D.W. Stokes, J.H Li, R.L. Forrest1, S.L. Ammu, J.C. Lenzi, S.C. Moss, B.Z. Nosho2,3, E.H. Aifer2, B.R. Bennett2and L.J. Whitman2 University of Houston, Department of Physics, Houston, TX, 77204, USA 1 University of Houston-Downtown, Department of Natural Sciences, Houston, TX 77002, USA 2 Naval Research Laboratory, Washington, DC, USA 3 Current address: HRL Laboratories, LLC, Malibu, CA 90265, USA
ABSTRACT The nanostructures self-organized via lateral composition modulation in 140 period (InAs)13/(GaSb)13 superlattices grown by molecular beam epitaxy have been studied by highresolution x-ray diffraction and infrared absorption. Three samples were analyzed in this study; two with lateral composition modulation and one without. X-ray reciprocal space map scans were taken to determine the average morphology of the modulated structures. Both vertical and lateral satellite peaks were observed for the samples with composition modulation, indicating the formation of two-dimensional nanowire arrays. The vertical wavelength measured for the two samples was twice the period intended by the growers. This is due to the face-centered cubic type stacking of the nanowires. Infrared absorption spectra of these two samples were compared to the spectra of the sample with no lateral composition modulation. Transitions involving the heavy- and light-hole bands in the GaSb hole quantum well and the electron subbands of the InAs electron quantum well were not evident for the samples with lateral composition modulation, indicating that the nanostructure of the lateral composition modulation affects the optical response of the sample, which is important for optoelectronic device applications. INTRODUCTION Type-II InAs/GaSb superlattices (SL) have demonstrated the unique ability to provide optical bandgaps over a wavelength range from 3-30 µm. With the valance band of GaSb higher in energy than the conduction band of InAs, a superlattice composed of thin layers of these materials results in alternating square well potentials for holes and electrons. When the quantum confinement effects of these wells overcome the negative gap of the bulk bandstructure, without fully localizing carriers in the wells, an artificial narrow gap semiconductor is created. The bandgap (and dispersion) of the superlattice is controlled by the thickness of the InAs and GaSb layers, and the composition of the interfaces. The additional properties of reduced Auger recombination and tunneling rates relative to other material systems with comparable bandgaps have resulted in great interest in the InAs/GaSb system for applications as lasers and detectors from the mid to very long-wave IR 1-7. Much investigation, however, is needed on basic materials issues, such as anion intermixing, interfacial roughness, as well as phenomena leading to the structural instability which is the subject of the present study, described below. Recently, lateral composition modulation (LCM) was observed in InAs/GaSb superl
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