Bulletin of the American Physical Society
2006 APS March Meeting
Monday–Friday, March 13–17, 2006; Baltimore, MD
Session N17: Focus Session: Semiconductors for THz and IR I |
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Sponsoring Units: FIAP Chair: K. K. Choi, Army Research Laboratory Room: Baltimore Convention Center 313 |
Wednesday, March 15, 2006 8:00AM - 8:36AM |
N17.00001: Terahertz Semiconductor Detectors: Designs to Applications Invited Speaker: The work describes terahertz photon detectors based on semiconductor micro- and nano-structures using homojunctions, and heterojunctions. A Homojunction or HEterojunction Interfacial Workfunction Internal Photoemission (HIWIP or HEIWIP) infrared detector, formed by a doped emitter layer, and an intrinsic layer acting as the barrier followed by another highly doped contact layer, can detect Terahertz photons due to intraband transitions. The threshold can be tailored by adjusting the band offset between the emitter and the barrier. This principle can be used with any semiconductor material combination. HIWIPs have the same material (doped and undoped) in the emitters and barriers, while HEIWIPs have different band gap material in the two layers. The detection mechanism involves free carrier absorption in the emitter, followed by the internal photoemission of photoexcited carriers across the junction barrier, and then the collection of carriers by the applied electric field at the contacts. Utilization of nanoplasmonic resonances to enhance the terahertz absorption using engineered and self-assembled metal nanostructures on HEIWIP detectors will also be discussed. The metal nanostructures will act as enhanced frequency couplers, which will allow more efficient absorption of terahertz radiation as it is converted into surface plasmons. The near field of SPs will affect the electron gas in the photodetectors the same way as the far-field does. Thus the local field enhancement known for other phenomena and devices could be achieved. Work supported in part by US NSF and US Airforce. [Preview Abstract] |
Wednesday, March 15, 2006 8:36AM - 8:48AM |
N17.00002: III-V Semiconductor Diodes and the Terahertz Technology Gap Thomas Crowe The terahertz frequency band, spanning from roughly 100 GHz through 10 THz, is often sited as the most scientifically rich, yet unexplored region of the electromagnetic spectrum. Scientific applications include radio astronomy, chemical spectroscopy, plasma diagnostics, compact range radar, atmospheric remote sensing and electron paramagnetic resonance studies of organic molecules. Recently, many groups have developed rudimentary imaging systems for this frequency band, either for basic scientific investigations or defense and security scanners. However, the inherent difficulty of creating sources of terahertz power that are sufficiently powerful, tunable, reliable and robust is a primary difficulty. Researchers in the field generally speak of the terahertz technology gap, which spans the transition from classical electronics to quantum photonics. This talk will consider the nature of the terahertz technology gap and the technological transition from electronics to photonics. Efforts to develop useful sources and receivers of terahertz energy based on III-V semiconductor diodes will be discussed. Also, important recent results, including the development of all-solid-state sources and receivers for the 0.1 -- 3 THz frequency range will be presented. Finally, the fundamental limitations of this technology will be considered. [Preview Abstract] |
Wednesday, March 15, 2006 8:48AM - 9:00AM |
N17.00003: Spontaneous emission from accelerated Bloch electrons -- Bloch oscillation radiation Valeriy Sokolov, Gerald Iafrate, Joseph Krieger A theory of spontaneous emission of radiation for a Bloch electron traversing a single band in an external electric field is presented. The radiation field is described by a free space quantized electromagnetic field in the Coulomb gauge. It is shown that the spontaneous emission occurs with frequencies equal to integral multiples of the Bloch frequency without any \textit{ad hoc} assumptions concerning the existence of Wannier-Stark levels. An explicit expression for the transition probability is derived in first-order perturbation theory relative to the radiation field. Although the output frequency of the radiation can be operationally tuned from the gigahertz to terahertz spectral range by varying the constant electric field, it is estimated that a spontaneous emission power output of only about 0.1 of a microwatt is available using GaAs-based superlattices. In this regard, it is noted that the atomic spontaneous emission probability and related transition rates can be enhanced by properly tailoring the surrounding electromagnetic environment. Therefore, considering Bloch oscillations in a resonant microcavity to enhance the spontaneous emission is a noteworthy alternative for exploring tunable gigahertz to terahertz radiation sources. [Preview Abstract] |
Wednesday, March 15, 2006 9:00AM - 9:12AM |
N17.00004: Developing a voltage tunable two-color corrugated QWIP focal plane array Kwong-Kit Choi, Carlos Monroy, Theodor Tamir, Ming Leung, Jinjin Li, Daniel Tsui Single color quantum well infrared photodetector focal plane array (QWIP FPA) has been fully developed. The trend is toward FPAs with spectral analysis and target discrimination capabilities. The challenges of achieving a two-color QWIP FPA are the identification of an effective coupling scheme for both wavelengths and a voltage tunable QWIP material. The former is needed to ensure high sensitivity in both wavelengths and the latter is needed in high resolution FPAs where only one external connection per pixel may be permissible. In this talk, we will discuss the detector parameters needed for high performance infrared imaging, the corrugated light coupling scheme, and the voltage tunable two-color QWIP materials based on superlattices (SLs). In the coupling design, one approach is to use Fabry-Perot oscillations in the triangular cavities to enhance both incident intensities. In the material design, the focus is on the electron energy relaxation rate in the energy relaxation layers (ERL) lying between the active SL periods. By computing the hot-electron distribution after traversing through the ERL layer, one can determine the doping required to eliminate cross-talk between the two colors. [Preview Abstract] |
Wednesday, March 15, 2006 9:12AM - 9:24AM |
N17.00005: Study of a broadband high-gain InGaAs/InGaAsP quantum-well infrared photodetector J. Li, K.K. Choi, J.F. Klem, J.L. Reno, D.C. Tsui Lattice-matched InGaAs/InP quantum well infrared photodetectors (QWIPs) exhibit high photoconductive gain but nonadjustable detection wavelength because of their fixed barrier height. The use of In$_{x}$Ga$_{1-x}$As$_{y}$P$_{1-y}$ (InGaAsP) as the barrier material is superior to that of InP with regard to flexibility of the operating wavelength. In this work we investigate the use of InGaAsP barriers in QWIPs for long-wavelength infrared detection applications. We studied a broadband quantum well InGaAs/InGaAsP detector covering 8-14 $\mu $m and found excellent agreement between observed and calculated responsivity spectra. This result shows the validity of our design model. To determine the usefulness of InGaAsP in long-wavelength detection, we also designed a GaAs/AlGaAs quantum well detector with a similar spectrum and compared its performance with that of the InGaAs/InGaAsP detector. Dark current noise measurement indicates that the gain of InGaAsP is 4.6 times larger than that of AlGaAs, showing that InGaAsP is a good candidate for long-wavelength high-speed infrared detection. [Preview Abstract] |
Wednesday, March 15, 2006 9:24AM - 9:36AM |
N17.00006: Interfaces as tools in the design of short period type-II InAs/GaSb superlattices for mid-IR detection Frank Szmulowicz, Heather Haugan, Gail Brown, K. Mahalingam, B. Ulrich, S. Munshi The effect of interface anisotropy on the electronic structure of InAs/GaSb type-II superlattices is exploited in the design of thin-layer superlattices for mid-IR detection threshold. The design is based on a theoretical envelope function model that incorporates the change of anion and cation species across InAs/GaSb interfaces, in particular, across the preferred InSb interface. The model predicts that a given threshold can be reached for a range of superlattice periods with InAs and GaSb layers as thin as a few monolayers. A number of superlattices with periods ranging from 50.6 to 21.2 angstroms for the 4 micron detection threshold were grown by molecular beam epitaxy based on the model design. Low temperature photoluminescence and photoresponse spectra confirmed that the superlattice band gaps remained constant at 330 meV although the period changed by the factor of 2.5. [Preview Abstract] |
Wednesday, March 15, 2006 9:36AM - 9:48AM |
N17.00007: Quantum Hall Devices as efficient and fast THz photodetectors Nikolai G. Kalugin, Christian Stellmach, Yuri B. Vasilyev, Rene Bonk, Alexander Hirsch, G\"{u}nter Hein, Georg Nachtwei Efficient THz photodetectors on the basis of quantum Hall (QH) system have been developed during the recent years. Engineering of the device shape and selection of the parameters of operation allow to implement QH detectors with response times ranging from 10 ns to milliseconds. The spectral resolution of QH detectors, ranging between 1-2 meV at energies of 8-12 meV of the incoming radiation, is a function of the electron mobility and of the bias voltage. QH photodetectors are tunable by the magnetic field and a gate voltage. The combination of these properties together with the high sensitivity of QH THz detectors serves as a basis for an implementation of reliable spectrometer-on-chip devices for THz spectroscopy and imaging. [Preview Abstract] |
Wednesday, March 15, 2006 9:48AM - 10:00AM |
N17.00008: Type-II Strained Layer InAs-GaSb Superlattice Photodiodes For Long Wave IR Detection Mark Field, Gerard Sullivan, Amal Ikhlassi, Berindar Brar, Michael Flatte, Christopher Grein, Michael Weimar We have fabricated and tested p-i-n photodiodes in InAs-GaSb superlattice material with measured cutoff wavelengths from 8.5 -- 10 $\mu $m, and compared their performance with mercury cadmium telluride (MCT) detectors of the same cutoff wavelengths. Impedance area (R0A) products approaching the MCT devices have been demonstrated with quantum efficiencies of over 14 {\%} per micron depth of the intrinsic layer. Progress towards designs with longer cutoff wavelengths, up to 16 $\mu $m, will be discussed along with issues and latest results on fabrication of a focal plane array using this material. [Preview Abstract] |
Wednesday, March 15, 2006 10:00AM - 10:12AM |
N17.00009: Electro-optically tunable compact terahertz source Dong Wu The promise of terahertz technology for surveillance and reconnaissance applications is huge. Despite the technical advantages, the major challenge today in terahertz technology is the development of a portable high-power terahertz source. Of the several available terahertz source technologies those based on the difference frequency technique are very promising, as they can produce a relatively high power terahertz beam over the frequency from 100 GHz to 3.5 THz, which is tunable. However, earlier this technique suffered from a high loss of terahertz signal, and produced a weak terahertz beam, in part due to a large impedance mismatching. Also its frequency tuning was cumbersome and its tuning range was limited since it was typically performed by rotating a nonlinear optical crystal against the pumping beam. In our recent experiments we modified the technique to improve the impedance matching and to replace the mechanical tuning with an electro-optical tuning. With this new technique we demonstrated a terahertz beam output power exceeding 10 mW (occasionally $\sim $ 100 mW) at frequencies around 1 THz. Our new technique the frequency tuning is very convenient and not limited by the geometry of the experimental set up. Detailed experiments and experimental results will be discussed [Preview Abstract] |
Wednesday, March 15, 2006 10:12AM - 10:24AM |
N17.00010: Terahertz time domain spectroscopy of hollow polycarbonated metal waveguides Aparajita Bandyopadhyay, Amartya Sengupta, John Federici, Valencia Johnson, James Harrington Recently, the terahertz region of the electromagnetic spectrum has gained critical significance in various technical applications and fundamental research problems, involving nondestructive evaluation of material parameters, bio-medical imaging, remote sensing and security screening. However, for applications in which THz radiation needs to be transmitted over a long distance without atmospheric absorption, a flexible waveguide could have potential applications simplifying the propagation of THz radiation in remote locations. Different structures like rigid hollow metallic waveguides, solid wires, or short lengths of solid-core transparent dielectrics such as sapphire and plastic have already been explored for THz guiding purposes. Recently, it has been reported that Cu coated flexible, hollow polycarbonate waveguide has a low loss of less than 4 dB/m in single mode operation, at 1.89 THz. In the present study, using a broadband THz source of photoconductive antennae, we characterize the loss and dispersion profile of Cu coated flexible, hollow polycarbonate waveguide having an inner diameter of 2mm. Insertion loss and the attenuation coefficient were calculated using waveguides of lengths between 40mm and 70mm. [Preview Abstract] |
Wednesday, March 15, 2006 10:24AM - 10:36AM |
N17.00011: Single Crystal Si Passive Optical Components for \textit{mm}-Astronomy Ari Brown, James Chervenak, David Chuss, Edward Wollack, Ross Henry, S. Harvey Moseley Construction of ultrasensitive, cryogenic-focal-planes for \textit{mm}-radiation detection requires simultaneous maximization of detector quantum efficiency and minimization of stray light effects, e.g., optical ``ghosting''. To achieve this task in the focal plane detector arrays of the Atacama Cosmology Telescope, integration of two technologies are envisioned; (1) an antireflective (AR) coating for reducing ghosting from the reflected component and increasing absorption at the focal plane, and (2) a backside absorber for suppressing reflections of the transmitted component. We propose a novel approach, involving single crystal Si components, to fabricate AR coatings and backside absorbers. AR coatings are made from Si dielectric honeycombs, in which their dielectric constant may be tuned via honeycomb dimension and wall thickness. Backside absorbers consist of AR Si honeycomb coated-resistors, and the resistors consist of P-implanted Si wafers. This approach enables us to circumvent the mechanical complexities arising from thermal expansion effects, because the detector array, back-short, and AR coating are fabricated out of the same material. We also extend the functionality of single crystal Si in the field of \textit{mm}-radiation detection by fabricating curved, low-loss, broadband waveguides. These waveguides may enable compact structures for applications requiring variable pathlength, e.g., interferometric spectroscopy. [Preview Abstract] |
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