Bulletin of the American Physical Society
2007 APS March Meeting
Volume 52, Number 1
Monday–Friday, March 5–9, 2007; Denver, Colorado
Session Y39: Focus Session: Physics & Technology of III-V Semiconductors in Infrared & THz Imaging II |
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Sponsoring Units: FIAP Chair: Nancy Haegel, Naval Postgraduate School Room: Colorado Convention Center 502 |
Friday, March 9, 2007 11:15AM - 11:51AM |
Y39.00001: Passive THz Imaging with Superconducting NbN microbolometer Arrays Invited Speaker: Passive THz imaging applications indoors require temperature difference resolution well below 1 K and integration times down to 0.1 ms. Recently we have shown that such resolution, approaching the photon noise limit, can be achieved using an antenna-coupled superconducting microwire bolometer with about 10 K transition temperature. The bolometer signal is read out with a low-noise room-temperature amplifier, thus eliminating the need for SQUID amplifiers. The readout method utilizes electro-thermal feedback at the $I-V$ curve minimum of a voltage-biased bolometer. At this working point, the very high power gain of the bolometer makes noise matching of the readout to the detector straightforward. The readout amplifier can be used with transition bolometers and calorimeters operating even at mK temperatures. We are presently developing a video-rate THz imager for concealed weapon detection, utilizing conical scanning and a 128-pixel NbN bolometer array, cooled down to 4 K with a pulse-tube cryocooler. We will characterize the bolometer arrays and the readout electrically and compare the results with the theory. We will also present the design of the system and results of preliminary imaging experiments. The work is done in collaboration between VTT, Millilab and NIST. [Preview Abstract] |
Friday, March 9, 2007 11:51AM - 12:03PM |
Y39.00002: Short-period InAs/GaSb superlattices for mid-infrared photodetectors. H.J. Haugan, F. Szmulowicz, G.J. Brown, B. Ullrich, S.R. Munshi, J.C. Wickett, D.W. Stokes Using a newly developed envelope function approximation model that includes interface effects, several InAs/GaSb type-II superlattices (SLs) were designed for uncooled mid-infrared detector applications. The 4 micron cutoff could be achieved with several SL designs. Superlattices with shorter-periods have larger intervalence band separations than larger-ones, which could increase the optical signal and reduce the detector noise, thus making room temperature operation possible. To test these possibilities, several short-period SLs were grown by molecular-beam epitaxy and their optical properties with reducing SL period were studied by band-edge absorption, photoconductivity and photoluminescence measurements. [Preview Abstract] |
Friday, March 9, 2007 12:03PM - 12:15PM |
Y39.00003: Demonstration of interface-scattering-limited electron mobilities in InAs/GaSb superlattices F. Szmulowicz, S. Elhamri, H. Haugan, G. Brown, W. Mitchel In-plane transport in InAs/GaSb type-II superlattices (SLs) is a sensitive indicator of SL growth quality and of the eventual performance of devices made from these materials. The in-plane mobility of electrons that move predominantly in the InAs layer is affected by a number of intrinsic and extrinsic scattering mechanisms, including interface roughness scattering (IRS). The hallmark of classic IRS-limited transport in SLs and quantum wells is the sixth power dependence of mobility on layer width. While IRS-limited transport was demonstrated in a number of SL and quantum well systems, it has never been demonstrated in the important InAs/GaSb SL material. We performed temperature dependent Hall effect measurements on a series of InAs/GaSb SLs with a fixed GaSb layer width and a variable InAs layer width, $d$. The low temperature (10K) in-plane electron mobilities, $\mu $, as a function $d$ behave as $\mu \propto d^{6.20}$, which follows the classic sixth power dependence expected from theory. [Preview Abstract] |
Friday, March 9, 2007 12:15PM - 12:27PM |
Y39.00004: GaAs based antenna-coupled terahertz detector operating at 300 K Sangwoo Kim, Jeramy Zimmerman, Paolo Focardi, Dong Ho Wu, Arthur C. Gossard, Mark S. Sherwin A Terahertz detector which consists of twin-slot antennas, coplanar waveguides, and a GaAs Metal Semiconductor-Field-Effect-Transistor (MESFET) has been developed. This talk will present design, fabrication, and recent measurements of our detector. As Terahertz photons are coupled into the antenna, an oscillating electric field is formed across the two gates of the GaAs MESFET. Then the oscillating electric field excites collective motion of the electron plasma in the active area, thereby changing the source-to-drain resistance of the transistor. The impedances of the antenna and the transistor were matched in order to maximize the power coupling efficiency. Our device is designed to have electronics-limited response time ($\sim $1 ns), broadband ($\sim $0.5 THz, HWHM) response, low Noise Equivalent Power (NEP) ($\sim $10$^{-10}$ Watt/(Hz)$^{1/2})$, responsivity of $\sim $1000 V/W, and ability to operate at room temperature. [Preview Abstract] |
Friday, March 9, 2007 12:27PM - 12:39PM |
Y39.00005: Near-Infrared In$_{0.53}$Ga$_{0.47}$As / AlAs$_{0.56}$Sb$_{0.44}$ Quantum Cascade Detectors Fabrizio Giorgetta, Esther Baumann, Christian Manz, Quankui Yang, Klaus Koehler, Daniel Hofstetter Quantum cascade detectors (QCDs) are a promising approach for photovoltaic electro-optical detectors in the infrared. They are based on intersubband transition, which makes them intrinsically fast due to the short unipolar relaxation times. Furthermore, no dark current noise occurs in QCDs because of the biasless operation. So far, QCDs with operating wavelengths down to 5 $\mu $m were demonstrated. For shorter wavelengths, a material system with a large conduction band discontinuity $\Delta $E$_{c}$ is required. A suitable choice is In$_{0.53}$Ga$_{0.47}$As / AlAs$_{0.56}$Sb$_{0.44}$ lattice matched to InP, with $\Delta $E$_{c}$=1.6 eV. We therefore present three InGaAs / AlAsSb QCDs detecting down to 2 $\mu $m. The exact well and barrier widths were determined by a self-consistent Schroedinger-Poisson solver and the samples were then grown by molecular beam epitaxy. The spectral room temperature responsivity of the three samples peaks at 2.34 $\mu $m (R$_{max}$=23 mA/W), 2.37 $\mu $m (16 mA/W), and 2.03 $\mu $m (4.3 mA/W). [Preview Abstract] |
Friday, March 9, 2007 12:39PM - 12:51PM |
Y39.00006: Quantum efficiency of an InAs/GaSb type-II superlattice photodiode Shin Mou, Jian Li, Shun Lien Chuang We present the experimentally measured and theoretically modeled quantum efficiency of an $n$-on-$p$ InAs/GaSb superlattice photodiode with a cutoff wavelength of 7.5 microns. The model is based on an analytical photocurrent solution with all the parameters obtained by measurements. For instance, the optical absorption coefficient was obtained from transmission measurements and the transport parameters were obtained from electron beam induced current (EBIC) experiments. With an absorptive layer 1.15 micrometer thick, we show the space charge region contributes most of the photocurrent for this specific structure. We found a design consisting of a ternary InAs/InGaSb superlattice absorptive region with an improved absorption coefficient gives us 50 {\%} larger external quantum efficiency with a similar cutoff wavelength. This shows that engineering the quantum structure could optimize the quantum efficiency. [Preview Abstract] |
Friday, March 9, 2007 12:51PM - 1:03PM |
Y39.00007: Molecular Beam Epitaxy Grown Long Wavelength Infrared HgCdTe on Compliant Si Substrates Priyalal Wijewarnasuriya, Yuanpin Chen, Gregory Brill, Nibir Dhar, Michael Carmody Large format, low cost, reliable and high performance infrared focal plane arrays (IRFPA) are essential for the Army's Third Generation IR Imaging Technology. Bulk-grown Cd$_{0.7}$Zn$_{\sim 0.3}$Te (CZT) substrates are the natural choice for HgCdTe epitaxy since it is lattice matched to HgCdTe alloy. However, a lack of large area CZT substrates, high production costs, and more importantly, the difference in thermal expansion coefficients between CZT substrates and silicon readout integrated circuits are some of the inherent drawbacks of CZT substrates. Consequently, Hg$_{1-x}$Cd$_{x}$Te detectors fabricated on silicon substrates are an attractive alternative generating considerable interest. Recent developments in the MBE Chalcogenide buffer layer growth technology on Si substrates has revolutionized the HgCdTe research and offered a new dimension to HgCdTe-based IR technology. We have fabricated large format 256x256 pixels with 40 microns pitch on LW-MBE-HgCdTe material grown on compliant CdSeTe/Si and CdTe/Si substrates. This paper will present data on 256x256 FPA and single device performance. [Preview Abstract] |
Friday, March 9, 2007 1:03PM - 1:15PM |
Y39.00008: Monolithic Mid-Infrared Photonic Integration of a Quantum Cascade Laser and a Passive Semiconductor Waveguide Kale J. Franz, Claire Gmachl, Kuen-Ting Shiu, Stephen R. Forrest On-chip integration of a quantum cascade (QC) laser with a passive semiconductor waveguide is reported. We use conventional semiconductor processing techniques to fabricate a QC laser directly coupled to a passive waveguide, where the unbiased active region and the lower cladding layers of the QC laser are used as the waveguide. The QC architecture is compatible with this technique due to the different allowed optical transitions when the QC structure is biased (for laser operation) and unbiased (for the passive waveguide). Thus the same epitaxial layers are made to emit light under bias and not absorb that same light when unbiased. The waveguide portion of the structure is fabricated by using a selective etch to remove the top InP cladding layers above the QC active core. We find the effective refractive index contrast provided by the etch step between the laser and waveguide to be sufficient for providing optical feedback for the laser. For our structure, we calculate a laser-waveguide ``facet'' reflectivity of about 3{\%} based on a 25{\%} increase in threshold current density compared to the same laser structure with two cleaved facets. [Preview Abstract] |
Friday, March 9, 2007 1:15PM - 1:27PM |
Y39.00009: A THz niche for AlP/GaP quantum wells M. Goiran, J. Galibert, J. L\'eotin, V.V. Rylkov, M. Semtsiv, O. Bierwagen, W.T. Masselink The development of THz spectroscopy and imaging based on intersubband transitions in Quantum Cascade Lasers (QCL) is precluded to date in the wavelength range 20-60 $\mu $m (15-5 THz) because of the reststrahl band of currently used GaAs alloy materials. One option to overcome this limitation is to use AlP/GaP Quantum wells grown on a GaP substrate, but until recently the intersubband structure of AlP quantum wells was unknown, because the X-conduction band structure of AlP was not established. We report on subband energy spectrum of electrons in AlP quantum wells as the outcome of recent effective mass measurements and valley-degeneracy, including the effect of strain caused by lattice mismatch between AlP and GaP [1]. We show that depending on the well thickness, the ground state subband has X$_{z}$ symmetry for well thickness shorter than 5nm and X$_{xy}$ symmetry for larger thickness. The knowledge of subband parameters in AlP/GaP quantum wells allows the design of both QCLs and QW detectors, taking into account the unique multi-valley subband structure of AlP quantum wells. [1] M.P. Semtsiv et al. Phys. Rev. B \textbf{74}, 041303(R) (2006) [Preview Abstract] |
Friday, March 9, 2007 1:27PM - 1:39PM |
Y39.00010: In-plane integration of quantum-cascade lasers with resonant intersubband nonlinearities Alexey Belyanin, Feng Xie, Venkata R. Chaganti, Don Smith We have recently demonstrated that the active region of a quantum cascade laser can be integrated with a cascade of intersubband transitions designed for the intracavity nonlinear frequency conversion of laser light. Integration has been implemented in the growth direction by vertically stacking the nonlinear region and active laser stages. While this approach is easy to realize, it has limited ability to control frequency and conversion efficiency of the nonlinear signal. Here we propose in-plane integration strategy, in which the laser is divided into two separately contacted and biased sections along the cavity length. One section operates as a laser active medium while another section serves as a nonlinear element. The sections share the same layer structure but may have very different set of electron states depending on the applied biases. We show that such schemes turn out to be surprisingly flexible in implementing various optical nonlinearities. The proposed approach enables convenient and broad tuning by applied voltage and extends the room-temperature operation range of quantum cascade lasers to very short (2.5-4 $\mu $m) or very long (THz) wavelengths. [Preview Abstract] |
Friday, March 9, 2007 1:39PM - 1:51PM |
Y39.00011: ABSTRACT WITHDRAWN |
Friday, March 9, 2007 1:51PM - 2:03PM |
Y39.00012: ABSTRACT WITHDRAWN |
Friday, March 9, 2007 2:03PM - 2:15PM |
Y39.00013: Propagation of Guided Modes in Curved Nanoribbon Waveguides Zhuo Ye, Xinhua Hu, Ming Li, Kai-Ming Ho, Peidong Yang We develop a planewave-based transfer matrix method in curvilinear coordinates to study the guided modes in curved nanoribbon waveguides. The problem of a curved structure is transformed into an equivalent one of a straight structure with spatially-dependent tensors of dielectric constant and magnetic permeability. The dispersion curves, mode profiles, and self-transmission of guided modes are obtained for the curved waveguides. Oscillations in the self-transmission as a function of wavelength are found to increase in amplitude as the bend becomes sharper. The period of the oscillations decreases with increase in size of the bending region. We show that curved sections can result in strong oscillations in the transmission spectrum similar to the recent experimental results in [M. Law, D. J. Sirbuly, J. C. Johnson, J. Goldberger, R. J. Saykally, P. Yang, Science\textbf{ 305}, 1269(2004)]. [Preview Abstract] |
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