Thick barium hexaferrite ͓BaO• ͑Fe 2 O 3 ͒ 6 ͔ films, having the magnetoplumbite structure ͑i.e., Ba M͒, were epitaxially grown on c-axis oriented GaN/ Al 2 O 3 substrates by pulsed laser deposition followed by liquid phase epitaxy. X-ray diffraction showed ͑0,0,2n͒ crystallographic alignment with pole figure analyses confirming epitaxial growth. High resolution transmission electron microscopy images revealed magnetoplumbite unit cells stacked with limited interfacial mixing. Saturation magnetization, 4M s , was measured for as-grown films to be 4.1Ϯ 0.3 kG with a perpendicular magnetic anisotropy field of 16Ϯ 0.3 kOe. Ferromagnetic resonance linewidth, the peak-to-peak power absorption derivative at 53 GHz, was 86 Oe. These properties will prove enabling for the integration of low loss Ba M ferrite microwave passive devices with active semiconductor circuit elements in systems-on-a-wafer architecture.

SummaryEmploying exit-plane wave function (EPWF) reconstruction in high-resolution transmission electron microscopy (HRTEM), we have developed an approach to atomic scale compositional analysis of III-V semiconductor interfaces, especially suitable for analyzing quaternary heterostructures with intermixing in both cation and anion sub-lattices. Specifically, we use the focal-series reconstruction technique, which retrieves the complex-valued EPWF from a thru-focus series of HRTEM images. A study of interfaces in Al 0.4 Ga 0.6 As-GaAs and In 0.25 Ga 0.75 Sb-InAs heterostructures using focal-series reconstruction shows that change in chemical composition along individual atomic columns across an interface is discernible in the phase image of the reconstructed EPWF. To extract the interface composition profiles along the cation and anion sub-lattices, quantitative analysis of the phase image is performed using factorial analysis of correspondence. This enabled independent quantification of changes in the InGa and As-Sb contents across ultra-thin interfacial regions (approximately 0.6 nm wide) with true atomic resolution, in the In 0.25 Ga 0.75 Sb-InAs heterostructure. The validity of the method is demonstrated by analyzing simulated HRTEM images of an InAs-GaSb-InAs model structure with abrupt and graded interfaces. Our approach is general, permitting atomic-level compositional analysis of heterostructures with two species per sub-lattice, hitherto unfeasible with existing HRTEM methods.

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Modification of the optical reflectance spectra of epitaxial gallium arsenide by weak magnetic fields J. Appl. Phys. 112, 073513 (2012) Nanocluster Si sensitized Er luminescence: Excitation mechanisms and critical factors for population inversion Appl. Phys. Lett. 101, 141907 (2012) Hyperspectral optical near-field imaging: Looking graded photonic crystals and photonic metamaterials in color Appl. Phys. Lett. 101, 141108 (2012) Photonic crystal fabrication in lithium niobate via pattern transfer through wet and dry etched chromium mask J. Appl. Phys. 112, 074303 (2012) Optically induced two-dimensional photonic quasicrystal lattices in iron-doped lithium niobate crystal with an amplitude mask Abstract. InAs/GaSb superlattice (SL) materials are of great interest for infrared (IR) detection applications. There is tremendous design flexibility in these superlattices but every design change has an impact on the epitaxial growth conditions for optimized performance. In here, we discuss how a simple design change of InAs width affects the material properties. As the InAs layer thickness increases from 9 monolayers (MLs) to 16 MLs for a fixed GaSb layer thickness of 7 MLs, the spectral intensity measured by photoconductivity decreases by two orders of magnitude, while the calculated absorption strength decreases by less than a factor of two. Since the measured transport properties of mid-wavelength infrared (MWIR) and long-wavelength infrared (LWIR) SLs were very different-majority carriers in MWIR (LWIR) SLs were holes (electrons)-the large decrease in the photoresponse is due to changes in extrinsic material factors that affect these charge carrier properties.

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