Calendar

Oct
17
Thu
SSEP Seminar – Plasmonics: Beyond the Glamour. Loss and its Mitigation. @ 260 Dreese Laboratory
Oct 17 @ 5:30 pm

Plasmonics: beyond the glamour. Loss and its Mitigation – Prof. Jacob Khurgin, ECE Department, Johns Hopkins University

Abstract: Recent years have seen staggering growth of interest in using nanostructured metals in optical range with the goal of enhancing linear and nonlinear optical properties or even engineering novel optical properties unknown in Nature – usually this burgeoning field is referred to as “Plasmonics and Metamaterials”.  After the initial years of excitement the community is belatedly beginning to recognize that loss in the metal is an important factor that might impede practical application of plasmonic devices, be it in signal processing, sensing, imaging or more esoteric applications like cloaking. Yet there is still an optimism that the loss can be either cleverly “designed away”, compensated by gain, or a new lossless materials can be found. In this talk we examine these concepts one by one and find that they all have limitations. First we show that when it comes to enhancing the device performance (solar cells, sensors, nonlinear optical devices, etc.) only the most inefficient devices can be improved by plasmonics while the performance of any decent device will only degrade. Then we demonstrate that in truly sub-wavelength metal structures the metal loss is inherent and cannot be engineered away by crafty changes in shape. Graphene as an alternative plasmonic material will also be considered and found to fall well short of being a universal cure for plasmonic ills. We then consider the idea of compensating loss using semiconductor gain medium and demonstrate that required gain can never be achieved due to increase in recombination rates caused by Purcell effect. After that we consider the physics of losses in metals at optical frequencies and show that the nature of these losses is quite different from the losses in RF domain. We then show that negative dielectric constant at optical frequencies does not have to inevitably lead to large absorption, and guardedly point to the tentative way in which new materials with negative dielectric constant and very low loss  might be synthesized, thus restoring the faint hope for plasmonics.

 

Biography: Jacob B. Khurgin had graduated with MS in Optics from the Institute of Fine Mechanics and Optics in St Petersburg, Russia in 1979, where, naturally, he was had been earlier born. In 1980 he had emigrated to US, and, to his own great surprise, immediately landed what at a time seemed to be a meaningful job with Philips Laboratories of NV Philips in Briarcliff Manor, NY. There for 8 years he worked with various degrees of success on miniature solid-state lasers, II-VI semiconductor lasers, various display and lighting fixtures, X-ray imaging, and small appliances such as electric shavers and coffeemakers (for which he holds 3 patents). Simultaneously he was pursuing his graduate studies at Polytechnic Institute of NY (nowadays NYU School of Engineering) where he had received PhD in Electro-physics in Jan. 1987. In Jan. 1988, prompted by a promotion to a Department Manager, Khurgin’s industrial career came to an abrupt end, and he had joined the Electrical and Computer engineering department of Johns Hopkins University, where, despite his ever present reservations about that place, he had settled down and is currently a Professor.  His research topics over the years included an eclectic mixture of optics of semiconductor nanostructures, nonlinear optical devices, lasers, optical communications, microwave photonics, and condensed matter physics. Currently he is working in the areas of mid-infrared lasers and detectors, phonon engineering for high frequency transistors, disorder in condensed matter physics, plasmonics, coherent secure optical communications, silicon photonics, cavity optomechanics, and slow light propagation.  His publications include 6 book chapters, one book edited, 240 papers in refereed journals and 28 patents. Prof Khurgin had held a position of a Visiting Professor in an array of institutions of variable degrees of repute – Princeton, UCLA, Brown, Ecole Normale Superieure (Paris), Ecole Polytechnique (Paris) and so on. Prof. Khurgin is a Fellow of American Physical Society and Optical Society of America.

Jul
18
Fri
ECE Seminar: Marius Grundmann, University of Leipzig @ 260 Dreese Laboratories
Jul 18 @ 11:00 am – 12:00 pm

The OSU Electrical and Computer Engineering department is hosting a seminar by Marius Grundmann, one of the world’s leading experts on transparent conducting oxide.

Bipolar oxide electronics – Materials and Devices
Marius Grundmann, Universität Leipzig, Institut für Experimentelle Physik, Leipzig, Germany

Abstract
Recent advances in the fabrication of oxide and transparent p-conducting thin films are reported. In conjunction with n-type epitaxial ZnO on Al2O3 and amorphous ZTO (zinc tin  oxide) thin films, bipolar diodes with (by far) the highest rectification reported for oxide diodes are presented.
(i) p-type amorphous material derived from ZnCo2O4 spinel (ZCO) ZCO has been deposited at room temperature using pulsed laser deposition. Hetero pn-diodes have been fabricated with rectification beyond 1010 and are stable for at least a year [1]. JFETs with ZnO channel and p-type a-ZnCo2O4 gate exhibit on/off current ratio larger than 107 and low subthreshold slope of S = 91 mV/dec [2]. Fully amorphous diodes from a-ZCO/a-ZTO exhibit rectification larger than 106 [3].
(ii) p-type zincblende cuprous iodide (CuI) CuI is the first reported transparent conductive material [4]. We have fabricated CuI thin films using iodization of copper thin films and direct thermal evaporation [5]. We report epitaxial growth on ZnO(00.1) and NaCl(001). p-CuI/n-ZnO diodes exhibit rectification larger than 106 [6]. We report on transparent photovoltaic cells from p-CuI/n-ZnO hetero-structure diodes [7]. The device physics of type-II band alignment heterojunction diodes is discussed.
(iii) p-type amorphous nickel oxide (NiO) NiO is a well-known p-type oxide. a-NiO/ZnO pn-diodes have been fabricated with rectification beyond 1010, also a diode with type-II band alignment, exhibiting an ideality factor of 2. We report on (semi-)transparent photovoltaic cells from such diodes [7].
References
[1] F.-L. Schein, M. Winter, T. Böntgen, H. von Wenckstern, M. Grundmann, Appl.
Phys. Lett. 104, 022104 (2014)
[2] Friedrich-Leonhard Schein, Holger von Wenckstern, Heiko Frenzel, and Marius
Grundmann, IEEE Electron Device Letters 33, 676 (2012)
[3] P. Schlupp, H. von Wenckstern, M. Grundmann, unpublished
[4] K. Bädeker, Über die elektrische Leitfähigkeit und die thermoelektrische Kraft
einiger Schwermetallverbindungen, Ann. Physik 327, 749-766 (1907)
[5] M. Grundmann, F.-L. Schein, M. Lorenz, T. Böntgen, J. Lenzner, H. von
Wenckstern, phys. stat. sol. (a) 210(9), 1671-1703 (2013)
[6] F.-L. Schein, H. von Wenckstern and M. Grundmann: Appl. Phys. Lett. 102
(2013), p. 092109
[7] R. Karsthof, H. von Wenckstern, M. Grundmann, unpublished

Dec
5
Fri
SSEP/ECE Seminar: Subhananda Chakrabarti, IIT-Bombay @ 260 Dreese Laboratories
Dec 5 @ 9:30 am – 10:30 am

SSEP-ECE Seminar – Subhananda Chakrabarti, Dept. of Electrical Engineering, IIT-Bombay

Compound (GaAs and ZnO) based research at IIT Bombay: From Intersubband detectors and arrays to Homojunction LEDs

 December 5, 2014, 9:30am

260 Dreese Laboratory

 Abstract

Professor Chakrabarti’s seminar will focus on both coupled and uncoupled quaternary-capped In(Ga)As/GaAs Quantum Dot Intersubband detectors and focal plane arrays. The quaternary capped detectors have shown promise in terms of both high responsivity and detectivity. The strain coupling in the Quantum dots improved the thermal stability in term of photoluminescence. He will also discuss the implementation of these detectors in 320×256 focal plane arrays. The talk will also reveal some of IIT Bombay’s recent research on p-doping of ZnO.

 

Speaker Bio

Subhananda Chakrabarti obtained his M.Sc and Ph.D from the Department of Electronic Science, University of Calcutta. He worked as a Lecturer in Physics at St. Xavier’s College, Calcutta. He has remained a Senior Research Fellow with the University of Michigan, USA from 2001-2005, Senior Researcher with Dublin City University, Ireland from 2005-2006 and Senior Researcher (RA2) with University of Glasgow, UK from 2006-2007 before joining IIT Bombay in September 2007. Presently he is a Professor in the Dept. of Electrical Engineering, IIT Bombay. He has worked extensively on molecular beam epitaxial growth, characterization and fabrication of semiconductor optoelectronic materials and devices. He has published and presented more than 200 papers in international journals and conferences. He is also a reviewer of IEEE Photonics Technology letters, IEEE Journal of Quantum electronics, Material Research Bulletin etc. He has also coauthored a couple of book chapters on Intersubband quantum dot detectors. Presently, his research focusses on GaAs and ZnO-based materials and devices.

Mar
3
Thu
SSEP seminar- Zhichao Yang @ Dreese Laboratories 260
Mar 3 @ 2:30 pm – 3:30 pm

Please mark your calendars for the next SSEP seminar.

Title: Gallium Nitride Tunneling Hot Electron Transistors

Speaker: Zhichao Yang, ECE Department, The Ohio State University

When: 2.30 pm on Thursday, March 3

Where: DL 260

Abstract: We report our work on first III-Nitride Tunneling Hot Electron Transistors (THETA) with common-emitter current gain greater than 10 and RF performance. State of the art technology for high frequency high power applications is GaN HEMTs, which have successfully demonstrated cut-off frequency (fT) up to 454 GHz. Further increase of the cutoff frequency into the THz range is challenging, as lateral transistors are ultimately limited by the low saturated velocity and short channel effects.  Our approach is to adopt a vertical device geometry in which electrons move at ballistic velocities that can significantly lower the transit delay and enable high gain.

We will present the modeling and demonstration of GaN THETA devices with record gain and the RF performance. We will first discuss our work on ensemble Monte Carlo simulations to investigate the hot electron transport, and to understand the limitations on the device performance.  We will then discuss our initial studies that show the evidence of  leakage through random-alloy AlGaN (or InGaN) barriers, which prevent transistor operation. By introducing polarization-engineered barrier (PEB) between base and collector, leakage current was significantly suppressed and common-emitter modulation was observed. Using these techniques, common-emitter current gain of up to 14.5 was achieved with collector current density in excess of 40 kA/cm2. Finally, small signal current gain was measured in common-emitter configuration with fT up to 3GHz for the first time in a GaN THETA. The work described here lays the framework for a new generation of vertical high frequency GaN amplifiers.

Biography:  Zhichao Yang received his Bachelor of Science and Master of Science in Applied Physics and Physics at Beijing University of Aeronautics and Astronautics in 2007 and 2011, respectively. He is working towards his PhD with Prof. Siddharth Rajan in the ECE department of The Ohio State University since 2012. His research interests include transport studies on III-Nitrides, fabrication and characterization of GaN Hot Electron Transistors and Field Emitters.