Bulletin of the American Physical Society
APS March Meeting 2016
Volume 61, Number 2
Monday–Friday, March 14–18, 2016; Baltimore, Maryland
Session P9: Superlattices and Terahertz |
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Sponsoring Units: DCMP FIAP Room: 305 |
Wednesday, March 16, 2016 2:30PM - 2:42PM |
P9.00001: Broadband Midwave Infrared InAs/GaSb Superlattice Light-Emitting Diodes Russell Ricker, Sydney Provence, Dennis Norton, John Prineas, Thomas Boggess Broadband (3.0 $\mu $m to 5.0 $\mu $m) emission is reported from InAs/GaSb superlattice light-emitting diodes grown via molecular beam epitaxy . Stacked active regions, each with a different emission wavelength, were connected with tunnel junctions, resulting in multiple emission wavelengths in a monolithic structure. Eight active regions provided eight overlapping emission spectra, simulating a broadband spectrum. Chips with mesas of sizes ranging from 24 $\mu $m x 24 $\mu $m to 400 $\mu $m x 400 $\mu $m were fabricated and wire bonded to a leadless chip carrier (LCC). The LCC was mounted in a liquid nitrogen cryostat. At low input currents, distinct peaks were observed at 3.3 $\mu $m, 3.6 $\mu $m, 3.9 $\mu $m, 4.2 $\mu $m, 4.5 $\mu $m, 4.9 $\mu $m, and 5.3 $\mu $m. At high input currents a continuous spectrum was observed with a peak near 3.8 $\mu $m and with a full-width at half-maximum of 1.42 $\mu $m. In quasi-continuous operation at 77 K, radiances exceeding 0.35 W/cm$^{\mathrm{2}}$-sr in a Lambertian profile were achieved. Current dependent electroluminescent spectra measured at liquid nitrogen temperatures demonstrate the blending of the various colors from each stage into one smooth spectrum at high currents. [Preview Abstract] |
Wednesday, March 16, 2016 2:42PM - 2:54PM |
P9.00002: Long Minority Carrier Lifetimes in InAs/InAsSb Type-II Superlattices Yigit Aytac, Benjamin Olson, Jim K Kim, Eric A Shaner, Samuel Hawkins, John Klem, Michael Flatté, Thomas F Boggess Three unintentionally doped MWIR InAs/InAsSb type-II superlattices (T2SLs) were designed and grown to have 15 {\%} Sb content in their alloy layers. The individual layer thicknesses of InAs and InAsSb are systematically altered in configurations of 174/218, 87/109, and 65/82 ({\AA}/{\AA}) while the total absorber thickness is nominally 4 $\mu $m and the bandgap is approximately 5.2 $\mu $m for all the samples. A time- and temperature- dependent differential-transmission technique was used to evaluate the carrier lifetime of each of the samples. Significantly long minority carrier (MC) lifetimes of \textasciitilde 14 $\mu $s and \textasciitilde 19 $\mu $s were obtained for the sample with 174 {\AA} /218 {\AA} InAs/InAsSb layer ratio at the temperatures of 77 K and 125 K, respectively. The defect energy levels of the InAs/InAsSb T2SLs reported here are determined to be \textasciitilde 300 \textpm 25 meV relative to InAs valance band edge strained to GaSb. Additionally, the electron dominated Auger coefficients, C$_{\mathrm{n,\thinspace }}$are obtained from the excess carrier density and temperature dependent recombination rate data. These coefficients are found to increase with decreasing individual layer thickness values from 3.4 to 29.9 x 10$^{\mathrm{-27\thinspace }}$cm$^{\mathrm{6}}$/s at 77 K. [Preview Abstract] |
Wednesday, March 16, 2016 2:54PM - 3:06PM |
P9.00003: Towards the design of high performance IR photonics: Optical analysis of textured gallium antimonide surfaces Ella Wassweiler, John Prineas, Fatima Toor Gallium antimonide (GaSb) is used for fabrication of various optoelectronics devices, such as laser diodes, light emitting diodes, and photodetectors for the mid-infrared (MIR) wavelengths of 3 $\mu $m to 30 $\mu $m. Light extraction or collection efficiency of GaSb-based MIR devices can be significantly enhanced by surface texturing due to the density graded effect. However to the best of our knowledge no systematic study exists that analyzes the etch chemistries, surface textures and resultant reflectivity of GaSb surfaces. In this work we present the characterization of GaSb textures and how they correlate to reflectivity in the visible and MIR wavelengths. A parametric sweep of etch chemistries involving hydrofluoric acid (HF), hydrogen peroxide (H$_{2}$O$_{2})$, and citric acid (C$_{4}$H$_{6}$O$_{6})$ provide a variety of surface textures that correspond to low reflectivity in different wavelength regimes. The size of the surface features causes scattering in wavelengths of the same magnitude and as a result lower the reflectivity. In addition an analytical equation derived from our experimental data is presented that correlates reflectivity measurements to etch depth and wavelength, which can used to design high performance IR photonic devices. [Preview Abstract] |
Wednesday, March 16, 2016 3:06PM - 3:18PM |
P9.00004: \textbf{Bias activated dielectric response of excitons and excitonic Mott transition in quantum confined lasers structures. } Kanika Bansal, Amit Bhunia, Shouvik Datta, Marzook S Alshammari, Mohamed Henini In contrast to the widely reported optical techniques, there are hardly any investigations on corresponding electrical signatures of condensed matter physics of excitonic phenomena. We studied small signal steady state capacitance response in III-V materials based multi quantum well (AlGaInP) and MBE grown quantum dot (InGaAs) laser diodes to identify signatures of excitonic presence. Conductance activation by forward bias was probed using frequency dependent differential capacitance response (fdC/df), which changes characteristically with the onset of light emission indicating the occurrence of negative activation energy. Our analysis shows that it is connected with a steady state population of exciton like bound states. Calculated average energy of this bound state matches well with the binding energy of weakly confined excitons in this type of structures. Further increase in charge injection decreases the differential capacitive response in AlGaInP based diodes, indicating a gradual Mott transition of excitonic states into electron hole plasma. This electrical description of excitonic Mott transition is fully supplemented by standard optical spectroscopic signatures of band gap renormalization and phase space filling effects. [Preview Abstract] |
Wednesday, March 16, 2016 3:18PM - 3:30PM |
P9.00005: Effective chiral description of an exciton-polariton superfluid in one and two dimensions Manas Kulkarni, German Kolmakov There has been remarkable experiments recently on capturing hydrodynamic features of exciton-polariton condensates in optical microcavities which have potential implications for quantum and optical computing and information technologies. We present an effective chiral description for such one and two dimensional systems. This description captures the fingerprints of hydrodynamics, namely, nonlinearity, dispersion and dissipation. The resulting chiral equation for the condensate perturbation wave dynamics is found to be of the generalized-KdV-type. We describe the phenomenon of polariton shock waves, solitons and defects in such systems. Our mapping is expected to have broad implications for other systems and can further help one in engineering a delicate balance between the pump and damping to produce stable optical signals propagating in polariton circuits. [Preview Abstract] |
Wednesday, March 16, 2016 3:30PM - 3:42PM |
P9.00006: Optical bandgap determination of ultrathin amorphous films and superlattices Stylianos Siontas, Pei Liu, Paolo Longo, Alexander Zaslavsky, Domenico Pacifici Quantum size confinement effects determine the optical bandgap of ultrathin \textless 5 nm amorphous films and superlattices. Although widely used, the standard experimental approach of combining normal-incidence reflectance and transmittance measurements with a single-pass absorption model may not always provide reliable results. By using ultra-thin amorphous germanium (a-Ge) layers down to $d \quad =$ 2 nm thickness as an experimental platform, we show that a multiple-reflection interference model is necessary to provide a more accurate extraction of the absorption coefficient. We also compare the two most frequently-used analytical models (Tauc and Cody) used to extract the optical bandgap from the measured absorption coefficient and clearly demonstrate that the Cody model provides a more reliable bandgap dependence on $d$. Finally, we apply our proposed method to experimentally determine the optical bandgap of a-Ge/SiO$_{\mathrm{2}}$ superlattices with alternating layers of a Ge and SiO$_{\mathrm{2}}$ ranging from 2 to 30 nm. Such superlattice structures enable additional control over the optical bandgap that may prove useful for the fabrication of high-efficiency photodetectors and solar cells in the optical and near-infrared spectral ranges. [Preview Abstract] |
Wednesday, March 16, 2016 3:42PM - 3:54PM |
P9.00007: Imaging the Electronic States of a Two-Dimensional Assembled Quasicrystal Laura C. Collins, Thomas G. Witte, Rochelle Silverman, David B. Green, Kenjiro K. Gomes The behavior of electrons in a periodic lattice is well understood, but how do electrons move in quasicrystals, which are ordered but aperiodic? We used scanning tunneling microscopy and atomic manipulation to assemble a quasicrystal based on the Penrose tiling and we carried out scanning tunneling spectroscopy to study its electronic properties. Carbon monoxide molecules were arranged on Cu(111) to form a potential landscape. This constrained the electrons in the two-dimensional surface states to move along the edges of a Penrose tiling. We measured the differential conductance maps to visualize the electronic density of states of the assembled quasicrystal. The statistical analysis of these maps has been used to characterize the localization of the electronic states. [Preview Abstract] |
Wednesday, March 16, 2016 3:54PM - 4:06PM |
P9.00008: Conductivity Dynamics of the Metal-to-Insulator Transition in Nickelate Superlattices. Verner Thorsmolle, Jingdi Zhang, Srimanta Middey, Elsa Abreu, Gufeng Zhang, Jak Chakhalian, Richard Averitt Complexity in transition metal oxides can be understood as a delicate balance between competing interactions, which give rise to an energy landscape whose details are not easily discerned. An increasingly successful approach to tackle this problem is that of time resolved experiments, where the fundamental timescales of the system properties can be investigated through their response to appropriately chosen femtosecond photoexcitation. Ultrafast optical studies of the insulator-metal transition (IMT) in transition metal oxides are of particular interest in terms of dynamics and control. The perovskite nickelates (RE)NiO$_{3}$ have emerged as an important class of IMT materials, exhibiting rich phenomena across the rare earth (RE) series that includes La, Pr, Nd, Sm, Eu, Y, and Lu. Quite recently, the growth of nickelate superlattices (SL) has been achieved, offering a route to control the IMT. Here, we will present the results of optical-pump THz-probe investigations of the IMT dynamics in these novel heterostructures. [Preview Abstract] |
Wednesday, March 16, 2016 4:06PM - 4:18PM |
P9.00009: First-principles Study of Atomic Rearrangement in GeTe-Sb2Te3 Superlattice Young-Sun Song, Seung-Hoon Jhi GeTe-Sb2Te3 chalcogenide superlattices, known as interfacial phase change memories (iPCMs), have been claimed to outperform Ge-Sb-Te-based phase-change materials. Despite its great potential as next-generation non-volatile memory devices, we still lack clear knowledge of the phase change mechanism. According to a recent work, the phase change processes in iPCMs involve two-step atomic rearrangements of Ge-Te layers, but the detailed interatomic features still remain unresolved. In this work, we studied the nature of atomic layer rearrangements in iPCMs using first-principles calculations and the interatomic potential model. We used the climbing image nudged elastic band (CI-NEB) method to obtain the intermediate structures and energies during the rearrangement processes. Applying a simple interatomic potential model to in-between steps, we investigated the interatomic motion during the phase change process. We found that a few selected atomic pairs determine most the energy barrier and also the response to external pressures. [Preview Abstract] |
Wednesday, March 16, 2016 4:18PM - 4:30PM |
P9.00010: Experimental demonstration of Luneburg waveguides Christopher Jensen, William Zimmerman, David Lahneman, Todd Adams, Thomas Gresock, Kathryn Zander, Vera Smolyaninova, Igor Smolyaninov Transformation optics (TO) gives rise to numerous unusual optical devices, such as novel metamaterial lenses and invisibility cloaks. However, it is very difficult to create metamaterials with low-loss broadband performance, especially in the visible frequency range. In our TO devices we use metal/dielectric waveguides to emulate metamaterial properties [1]. Here we report the first experimental realization of TO Luneburg waveguides [2]. The individual Luneburg lenses in the fabricated design are based on lithographically defined metal/dielectric waveguides. We have studied wavelength and polarization dependent performance of the waveguides. Adiabatic variations of the waveguide shape enable control of the effective refractive index experienced by the TM light propagating inside the waveguide. Our experimental designs appear to be broadband, which has been verified in the 480-633 nm range. These novel optical devices considerably extend our ability to control light on sub-micrometer scales. [1]. V.N. Smolyaninova, et al., Phys. Rev. B 87, 075406 (2013); [2]. V.N. Smolyaninova, et al., Photonics 2, 440 (2015). This research was supported by the NSF grant DMR-1104676. [Preview Abstract] |
Wednesday, March 16, 2016 4:30PM - 4:42PM |
P9.00011: Terahertz radiation-induced sub-cycle field electron emission across a split-gap dipole antenna Jingdi Zhang, Xiaoguang Zhao, Kebin Fan, Xiaoning Wang, Gu-Feng Zhang, Kun Geng, Xin Zhang, Richard D. Averitt We use intense terahertz pulses to excite the resonant mode (0.6THz) of a micro-fabricated dipole antenna with a vacuum gap. The dipole antenna structure enhances the peak amplitude of the in-gap THz electric field by a factor of \textasciitilde 170. Above an in-gap E-field threshold amplitude of \textasciitilde 10 MVcm-1, THz-induced field electron emission is observed (TIFEE) as indicated by the field-induced electric current across the dipole antenna gap. Field emission occurs within a fraction of the driving THz period. Our analysis of the current (I) and incident electric field (E) is in agreement with a Millikan-Lauritsen analysis where log (I) exhibits a linear dependence on 1/E. Numerical estimates indicate that the electrons are accelerated to a value of approximately one tenth of the speed of light. (arXiv: 1508.04737) [Preview Abstract] |
Wednesday, March 16, 2016 4:42PM - 4:54PM |
P9.00012: Fabrication of THz Sensor with Metamaterial Absorber Hugo Gonzalez, Fabio Alves, Gamani Karunasiri The terahertz (THz) portion of the electromagnetic spectrum (0.1-10 THz) has not been fully utilized due to the lack of sensitive detectors. Real-time imaging in this spectral range has been demonstrated using uncooled infrared microbolometer cameras and external illumination provided by quantum cascade laser (QCL) based THz sources. However, the microbolometer pixels in the cameras have not been optimized to achieve high sensitivity in THz frequencies. Recently, we have developed a highly sensitive micromechanical THz sensor employing bi-material effect with an integrated metamaterial absorber tuned to the THz frequency of interest. The use of bi-material structures causes deflection on the sensor to as the absorbed THz radiation increases its temperature, which can be monitored optically by reflecting a light beam. This approach eliminates the integration of readout electronics needed in microbolometers. The absorption of THz by metamaterial can be tailored by controlling geometrical parameters. The sensors can be fabricated using conventional microelectronic materials and incorporated into pixels to form focal plane arrays (FPAs). In this presentation, characterization and readout of a THz sensor with integrated metamaterial structure will be described. [Preview Abstract] |
Wednesday, March 16, 2016 4:54PM - 5:06PM |
P9.00013: Nonperiodic metallic gratings transparent for broadband terahertz waves Ren-Hao Fan, Xiao-Ping Ren, Ru-Wen Peng, Xian-Rong Huang, Mu Wang Recently, we demonstrate both theoretically and experimentally that nonperiodic metallic gratings can become transparent for broadband terahertz waves. Quasiperiodic and disordered metallic gratings effectively weaken and even eliminate Wood's anomalies, which are the diffraction-related characters of periodic gratings. Consequently, both the transparence bandwidth and transmission efficiency are significantly increased due to the structural aperiodicity. Furthermore, we show that for a specific light source, for example, a line source, a corresponding nonperiodic transparent grating can be also designed. We expect that our findings can be applied for transparent conducting panels, perfect white-beam polarizers, antireflective conducting solar cells, and beyond. References: X. P. Ren, R. H. Fan, R. W. Peng, X. R. Huang, D. H. Xu, Y. Zhou, and Mu Wang, Physical Review B, 91, 045111 (2015); R. H. Fan, R. W. Peng, X. R. Huang, J. Li, Y. Liu, Q. Hu, Mu. Wang, and X. Zhang, Advanced Materials, 24, 1980 (2012); and X. R. Huang, R. W. Peng, and R. H. Fan. Physical Review Letters, 105, 243901 (2010). [Preview Abstract] |
Wednesday, March 16, 2016 5:06PM - 5:18PM |
P9.00014: Tuning the Polarization State of Light over a Broad Frequency Range with Metasurfaces Mu Wang, Shang-Chi Jiang, Zheng-Han Wang, Xiang Xiong, Ru-Wen Peng Controlling the polarization state, the transmission direction and the phase of light within a confined space is an important issue in optics. By integrating metallic metastructure and dielectric interlayer, it is possible to realize the dispersion-free broadband device on sub-wavelength scale, where the strong response of the metallic structures helps to decrease the device size while the dielectric interlayer helps to eliminate the dispersion simultaneously in both the amplitude and the phase difference of the reflected/transmitted light. As an examples to apply this concept, a broadband quarter-wave plate and a half-wave plate are experimentally demonstrated. By carefully selecting the structural parameters, the polarization state of light can be freely tuned across a broad frequency range, and all of the polarization states on the Poincaré sphere can be realized dispersion free. Some contents of this talk can be found in the following references: [1] S.-C. Jiang, et al., \textit{High-efficiency generation of circularly polarized light via symmetry-induced anomalous reflection, }\textbf{Physical Review B} 91, 125421 (2015), [2] S.-C. Jiang, et al., \textit{Controlling the Polarization State of Light with a Dispersion-Free Metastructure}, \textbf{Physical Review X} 4, 021026 (2014), [3] X. Xiong, et al., \textit{Metallic stereostructured layer: an approach for broadband polarization state manipulation, }\textbf{Applied Physics Letters} 105, 201105 (2014). [Preview Abstract] |
Wednesday, March 16, 2016 5:18PM - 5:30PM |
P9.00015: Freely-tunable broadband polarization rotator for terahertz waves Ru-Wen Peng, Ren-Hao Fan, Yu Zhou, Shang-Chi Jiang, Xiang Xiong, Xian-Rong Huang, Mu Wang It is known that commercially-available terahertz (THz) emitters usually generate linearly polarized waves only along certain directions, but in practice, a polarization rotator that is capable of rotating the polarization of THz waves to any direction is particularly desirable and it will have various important applications. In this work, we demonstrate a freely tunable polarization rotator for broadband THz waves using a three-rotating-layer metallic grating structure, which can conveniently rotate the polarization of a linearly polarized THz wave to any desired direction with nearly perfect conversion efficiency. The device performance has been experimentally demonstrated by both THz transmission spectra and direct imaging. The polarization rotation originates from multi wave interference in the three-layer grating structure based on the scattering-matrix analysis. We can expect that this active broadband polarization rotator has wide applications in analytical chemistry, biology, communication technology, imaging, etc.. Reference: R. H. Fan, Y. Zhou, X. P. Ren, R. W. Peng, S. C. Jiang, D. H. Xu, X. Xiong, X. R. Huang, and Mu Wang, Advanced Materials 27,1201(2015). [Preview Abstract] |
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