Bulletin of the American Physical Society
2006 APS March Meeting
Monday–Friday, March 13–17, 2006; Baltimore, MD
Session R17: Focus Session: Semiconductors for THz and IR II |
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Sponsoring Units: FIAP Chair: A. G. U. Perera, Georgia State University Room: Baltimore Convention Center 313 |
Wednesday, March 15, 2006 2:30PM - 2:42PM |
R17.00001: Dependence of the groundstate interband optical transition in InAs-GaSb superlattices on the width of the GaSb layers Patrick Folkes, J. Little, S. Svensson, K. Olver, A. Amtout, S. Krishna We have investigated the optical characteristics of a set of InAs-GaSb superlattice structures (SLS) which have InAs layers with a fixed width of 25 {\AA} and GaSb layers whose width varies from stucture to structure over the range 25 {\AA} to 100 {\AA}. Photoluminescence measurements were carried out over the range 10K -- 100K on the SLS. Using photodiodes fabricated from the SLS, measurements of the photocurrent-excitation energy spectrum and the time-resolved photoconductivity were carried out at 78K. The observed dependence of the relative oscillator strength of the SLS band-edge transition on the GaSb layer width will be compared with theory$^{1}$. The effect of defects on the the optical and transport properties of the SLS and the dependence of this effect on the GaSb layer width will be discussed. [Preview Abstract] |
Wednesday, March 15, 2006 2:42PM - 2:54PM |
R17.00002: Comparison of terahertz emission from N-face and In-face indium nitride thin films Grace Chern, Eric Readinger, Hongen Shen, Michael Wraback, Chad Gallinat, Gregor Koblmueller, James Speck Narrow band gap semiconductors are attractive as emitters of terahertz radiation when optically excited with femtosecond laser pulses. We present a comparison of THz emission from N-face and In-face indium nitride (InN) thin films. The InN samples are optically pumped with a 160 fs laser pulse at 800nm. The subsequent THz radiation is detected by ultrafast electro-optic sampling using a 2mm thick ZnTe crystal. The measured In-face InN films have a Hall mobility of 838 cm$^{2}$/Vs and 2098 cm$^{2}$/Vs, and the measured N-face InN samples have a Hall mobility of 645 cm$^{2}$/Vs and 1460 cm$^{2}$/Vs. For both polarities, we show an increase in THz power from InN with higher mobilities. However, THz radiation from the In-face InN sample with a Hall mobility of 2098 cm$^{2}$/Vs is lower in power than from the N-face InN film with a lower Hall mobility of 1460 cm$^{2}$/Vs. We attribute the lower THz power from In-face InN samples to lower crystalline quality of the In-face material, as determined by x-ray, TEM and photoluminescence measurements. The ratio of the defect density and the PL intensity between the In-face and N-face materials is approximately 3 and 10, respectively. [Preview Abstract] |
Wednesday, March 15, 2006 2:54PM - 3:06PM |
R17.00003: Electro-Optical characterization of W-structured type-II superlattice photodetectors J.G. Tischler, E.H. Aifer, I. Vurgaftman, J.R. Meyer, C.L. Canedy, E.M. Jackson Antimonide based superlattices (SLs) have shown promise as the next generation material system for very long wave infrared focal plane arrays. In particular, we investigated n-i-p diodes with ``W-structured'' type-II SLs, consisting of repetitions of AlGaInSb/InAs/InGaSb/InAs/AlGaInSb layers such that the bulk conduction band-edges of each period forms a ``W'' pattern. The performance of such photodiodes (PDs) depends on a combination of optical and transport properties, such as the absorption coefficient and minority carrier diffusion length. In order to optimize such devices, it is necessary to measure these properties independently. Using a combination of techniques such as transmission and photoluminescence (PL) spectroscopies, and black-body responsivity measurements, we have systematically studied and optimized our PDs. We have found that the most sensitive parameter that limits the PD performance is the carrier lifetime, making PL measurements the most sensitive characterization technique. We report PDs with up to 100{\%} charge collection efficiency and up to 35{\%} external quantum efficiency. [Preview Abstract] |
Wednesday, March 15, 2006 3:06PM - 3:42PM |
R17.00004: Recent development of terahertz wave sensing and imaging science, technology, and applications Invited Speaker: Recent advances in THz science and technology make it one of the most promising research areas in the 21st century for sensing and imaging, as well as in other interdisciplinary fields. We believe new T-ray capabilities will impact a range of interdisciplinary fields and industrial companies, including: communications, imaging, medical diagnosis, health monitoring, environmental control, and chemical and biological identification. While microwave and X-ray imaging modalities produce density pictures, T-ray imaging provides spectroscopic information within the THz frequency range. The unique rotational and vibrational responses of materials within the THz range provide information that is generally absent in optical, X-ray and NMR images. A THz wave can easily penetrate and inspect the insides of most dielectric materials, which are opaque to visible light and low contrast to X-rays, making T-rays a useful complementary imaging source in this context. Recent developments of THz wave technologies allow us to coherently control a THz wave (phase, amplitude, and directionality). I present its impacts the physics understanding and industrial applications. Examples of imaging a long distance target ($>$100 meters), large scale industrial samples ($>$m2), or a small scale semiconductor device (a few nanometer) will be presented. [Preview Abstract] |
Wednesday, March 15, 2006 3:42PM - 3:54PM |
R17.00005: Self-assembled ErAs nanoislands for enhanced terahertz detection. John O'Hara, Rohit Prasankumar, Josh Zide, Art Gossard, Antoinette Taylor, Richard Averitt Traditionally, THz detectors based on photoconductive (PC) antennas have utilized low-temperature grown GaAs (LT-GaAs) and radiation-damaged silicon-on-sapphire (RD-SOS) due to their fast carrier trapping times. However, the development of self-assembled ErAs nanoislands embedded in a GaAs matrix offers a particularly useful alternative for THz PC devices based on the ability to independently tune photo-excited carrier lifetimes, trap density, and dark resistance. In this work, we demonstrate enhanced THz detection using self-assembled ErAs:GaAs nanoisland structures. Three nearly identical THz PC antenna detectors are fabricated; one each on the LT-GaAs, RD-SOS, and ErAs:GaAs substrates. Their performance in a typical THz time-domain spectroscopy system is compared in terms of optical efficiency, bandwidth, and saturation behavior. Carrier lifetimes in all three substrates are also compared via pump-probe techniques. [Preview Abstract] |
Wednesday, March 15, 2006 3:54PM - 4:06PM |
R17.00006: Type II superlattice infrared focal plane arrays: Optical, electrical, and mid-wave infrared imaging characterization. John Little, Stefan Svensson, Arnie Goldberg, Steve Kennerly, Kim Olver, Trirat Hongsmatip, Michael Winn, Parvez Uppal We have studied the infrared optical and temperature dependent electrical properties of 320 x 256 arrays of GaSb/InAs type II superlattice infrared photodiodes. Good agreement between single-pixel and focal plane array measurements of the photon-to- electron/hole conversion efficiency was obtained, and the infrared absorption coefficient extracted from these measurements was found to be comparable to that of HgCdTe with the same bandgap as the type II superlattice. Temperature and voltage dependent dark current measurements and the voltage dependent photocurrent generated by a 300 K background scene were described well using a semi-empirical model of the photodiode. We will show high-quality images obtained from the mid-infrared focal plane array operating at 78 K. [Preview Abstract] |
Wednesday, March 15, 2006 4:06PM - 4:18PM |
R17.00007: Pulsed THz-emission and carrier concentrations in InN Ricardo Ascazubi, Ingrid Wilke, William Schaff InN grown on sapphire substrates with GaN or AlN buffer layers exhibits a variety of unique electronic properties for the development of brighter photo-conducting THz-radiation sources. Since InN is a narrow band gap semiconductor it is also an attractive candidate for compact and lightweight THz-spectroscopy and imaging systems based on femtosecond fiber laser operating at 1.55$\mu $m wavelength. The important properties of InN with regard to strong THz-emission are low probability of intervalley scattering and strong intrinsic electric fields near the surface. The electric fields at the InN surface are caused by a strong intrinsic electron surface accumulation. We report on THz-emission of n-type InN with carrier concentrations ranging from 10$^{17}$cm$^{-3}$ to 10$^{20}$cm$^{-3}$. We observe a strongly increasing THz-emission with decreasing carrier concentrations. Based on charge neutrality the dependence of THz-emission on carrier concentrations is explained by assuming an underpopulated region behind the surface accumulation layer, across which the surface field interacts with photo-injected carriers generating THz-transients. The surface state density calculated within this model agrees well data obtained by high resolution electron energy loss spectroscopy data. [Preview Abstract] |
Wednesday, March 15, 2006 4:18PM - 4:30PM |
R17.00008: A New All-Optical Imaging Scheme based on QWIP technology Debing Zeng, Gang Chen, Rainer Martini Infrared imaging applications have gained increasing interest over the recent decades due to favorable light propagation, night imaging as well as chemical sensing applications. However, the scalability of the existing techniques towards high resolution in the multi-megapixel range is one of the major challenges in today's IR imaging technologies. Here we present an alternative solution using an all-optical wavelength conversion scheme. QWIP has been successfully proven their potential in IR imaging applications. Yet the fundamental conversion process from IR light to electric current has been one of the major restrictions in such system. To overcome this problem we propose the use of an all-optical conversion scheme, which utilizes an interband resonant optical NIR beam to probe the electrical population of the QW structure. In this methodology the incident MIR radiation changes the occupation of the QWs, which in turn influences the NIR transmission. Hence the irradiated MIR images can be probed by spatially resolved measurement of the NIR transmission, as has been demonstrated by Nada et al. for all-optical switching purposes. In this talk we present an implementation scheme of the all-optical QWIP readout technique together with theoretical calculations of the sensitivity of the proposed device and its temperature dependence. First experimental results will be presented also. The Authors thankfully acknowledge financial support by US Army, Picatinny Arsenal. [Preview Abstract] |
Wednesday, March 15, 2006 4:30PM - 4:42PM |
R17.00009: A THz Microcavity with a Phononic Cavity Polariton Hadley Lawler, Sanjiv Shresta, Gavin Brennen Polaritons were originally considered within the context of the dielectric response of bulk systems, and its relation to the dispersion of fundamental solid-state excitations, such as excitons and optical phonons. More recently, excitonic cavity polaritons have been theoretically described and observed. These excitonic cavity polaritons represent a tunable Rabi coupling between a condensed matter excitation within a microstructure and a cavity-resonant electromagnetic mode. Like excitons, optical phonons possess well-characterized cross-sections with the electromagnetic field, but at lower energies and larger length and time scales. We present theory relevant to a phononic cavity polariton, discuss the prospects for the observation of such a system, and detail our progress toward the prediction of the Rabi coupling's variation with tunable parameters. While susceptibility-type measurements are a possible route for the detection of such a system, we emphasize the possibility of measuring the Rabi oscillation directly in the time domain using ultrafast lasers. [Preview Abstract] |
Wednesday, March 15, 2006 4:42PM - 4:54PM |
R17.00010: Interplay between plasmon and current due to terahertz radiation Danhong Huang, Casey Rhodes, Paul Alsing, Dave Cardimona A unique structure composed of a half-space of air and a semi- infinite n-doped bulk GaAs covered by a heavily-n-doped InAs conducting interface sheet is proposed to explore the physics behind the interplay between a transverse sheet current, evanescent modes, and a longitudinal field in the bulk. The presence of the 3D and 2D plasma waves and the sheet current enables the longitudinal and transverse electromagnetic oscillations to couple in directions both perpendicular and parallel to the conducting sheet. We derive a spatially- nonlocal dynamic theory in order to determine the effects of the longitudinal 3D plasma-wave excitation, transverse sheet current and 2D plasma waves, and evanescent modes on the enhancement of a transmitted near-E-field with an electromagnetic wave incident on our proposed structure. For p- polarized incident field, we find one sharp dip and a broad peak in the transmitted near-E-field due to absorption by the longitudinal 3D plasma wave and its coupling to the transverse sheet current. [Preview Abstract] |
Wednesday, March 15, 2006 4:54PM - 5:06PM |
R17.00011: Submicron Material Characterization Using Terahertz Scanning Near-Field Microscopy Hou-Tong Chen, Antoinette Taylor, Richard Averitt, Federico Buersgens, Roland Kersting The recent development of the apertureless terahertz scanning near-field optical microscope (THz-SNOM) allows for submicron spatial resolution [1] and enables a broad variety of novel applications in material characterization. The basic mechanism is that a metallic probe allows for mapping of the THz permittivity of a surface. In this contribution, we report on measurements of microscopic scale charge carrier distributions and dielectric contrast with sub-micrometer resolution in various material systems and structures using THz-SNOM. We have identified a novel imaging mechanism in terms of a configurational resonance [2], which contrasts the widely accepted scattering model at visible and near-infrared frequencies. ~[1] H.-T. Chen, et al., \textit{Appl. Phys. Lett.} \textbf{83}, 3009 (2003). ~[2] H.-T. Chen, et al., \textit{Phys. Rev. Lett.} \textbf{93}, 267401 (2004). [Preview Abstract] |
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