39th Int. Conf. on Infrared, Millimeter, and THz Waves
September 14-19, 2014
The University of Arizona, Tucson, AZ
M4/E - 12. Material Science II
Monday, September 15, 2014 4:00 pm to 5:30 pm
Room: Santa Rita Room
Chairperson: Roger Lewis
4:00 pm 4:00 pm : Investigation Of Silicon-Germanium Nanowires THz Emission
Presenter: Soner Balci

Semiconductor nanowires and nanostructures have a great potential for Terahertz generation and detection, especially because certain materials properties such as optical absorption, high electron and hole mobility, and short carrier lifetime can be engineered through structural changes and material compositions. In such structures, the variation in geometry and surface charge characteristics can greatly influence the dynamics of photoexcited carrier recombination, which is directly related to strength of the Terahertz emission. In this work, we studied theoretical and experimental investigation of carrier lifetime reduction and the properties of THz generation in SiGe nanowires. Both standard Terahertz time-domain spectroscopy, and optical pump and THz probe measurements were carried to investigate the material properties and high frequency carrier dynamics of Si1-xGex nanowires. A mobility of 1615 cm2/Vs and a carrier lifetime of ~0.24 ps were measured. The influence of carrier dynamics properties on the THz generation from SiGe nanowires was investigated in details.

Author(s):
Soner Balci - Electrical and Computer Engineering Department, University of Alabama
Woo-Jung Lee - Department of Physics and Applied Physics, Yonsei University
David Wilbert - Electrical and Computer Engineering Department, University of Alabama
Patrick Kung - Electrical and Computer Engineering Department, University of Alabama
Chul Kang - Gawangju Institute of Science and Technology
Mann-Ho Cho - Department of Physics and Applied Physics, Yonsei University
Seongsin Margaret Kim - Electrical and Computer Engineering Department, University of Alabama
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4:30 pm 4:30 pm : Terahertz Probing Of Local Electron States In PbTe(Ga)
Presenter: Dmitry Khokhlov

We report on unusual photoconductivity under the action of strong terahertz laser pulses in PbTe(Ga). The character and even the sign on the photoconductivity depends on the level of photoexcitation: it is positive and persistent at high degrees of excitation, whereas it is negative and non-persistent at low levels of excitation. We show that this non-trivial photoelectric behaviour is due to formation of local electron states in the close vicinity of the quasi-Fermi level. These local states may be formed only when the quasi-Fermi level lies on the background of an allowed energy band with relatively high density of states

Author(s):
Dmitry Khokhlov - M.V. Lomonosov Moscow State University
Svetlana Egorova - M.V. Lomonosov Moscow State University
Vladimir Chernichkin - M.V. Lomonosov Moscow State University
Ludmila Ryabova - M.V. Lomonosov Moscow State University
Andrey Nicorici - Institute of Applied Physics
Sergey Danilov - University of Regensburg
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4:45 pm 4:45 pm : Terahertz Response Of SrTiO3 Based Heterostructures: Influence Of Strain, Temperature And Electric Field
Presenter: Volodymyr Skoromets

A systematic study of strained SrTiO3/DyScO3 heterostructures was performed using time-domain terahertz spectroscopy in the temperature range from 20 to 294 K. Interdigitated electrodes deposited on top of the structures allowed probing of the terahertz response upon an applied electric field. We explored a possibility to increase the total thickness of SrTiO3 layers while maintaining the epitaxial strain which induces the ferroelectric phase transition. All studied structures underwent the phase transition close to room temperature. Evolution of the complex dielectric spectra with temperature and electric bias was described by a general model involving a harmonic oscillator (soft mode) coupled to a Debye relaxation (central mode). At high temperatures, the soft mode is responsible for nearly all the changes observed in the spectra with temperature and applied electric field. At low temperatures, deep in the ferroelectric phase, the soft mode significantly hardens and loses its importance for the terahertz dynamics; the central mode becomes stronger and it almost completely determines the shape of the measured spectra. The observed variation of the phase transition temperature and of the terahertz response among investigated structures was ascribed to a partial strain relaxation.

Author(s):
Volodymyr Skoromets - Institute of Physics, Academy of Sciences of Czech Republic
Christelle Kadlec - Institute of Physics, Academy of Sciences of Czech Republic
Jan Drahokoupil - Institute of Physics, Academy of Sciences of Czech Republic
J¸rgen Schubert - Peter Gruenberg Institute, J¸lich
Petr Kuûel - Institute of Physics, Academy of Sciences of Czech Republic
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5:00 pm 5:00 pm : Carrier Transport Of Conducting Polymer PEDOT:PSS Investigated By temperature Dependence Of THz And IR Spectra
Presenter: Yusuke Yamada

In this study, we have investigated the carrier transport mechanism of poly(3,4-ethylenedioxythiophene): poly(styrene- sulfonate) (PEDOT:PSS) by analyzing the temperature dependences of THz conductivity and infrared reflectance spectra with the series sequence of free and hopping carriers model (SSFHC model). It was found that the macroscopic carrier transport of PEDOT:PSS was dominated by the series sequence of the metallic transport in PEDOT nanocrystals and hopping conduction between PEDOT nanocrystals.

Author(s):
Yusuke Yamada - RIKEN RAP and Grad. Sch. Sci. Tohoku Univ
Masatsugu Yamashita - RIKEN RAP
Takahiko Sasaki - IMR Tohoku Univ
Hidenori Okuzaki - Inter.Grad. Sch. of Med. and Eng Univ. Yamanashi
Chiko Otani - RIKEN RAP and Grad. Sch. Sci. Tohoku Univ
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5:15 pm 5:15 pm : THz Wave Generation From Cesium Vapor
Presenter: Xuan Sun

Applications of THz photonics rely critically on efficient THz wave generation and detection. Here we report THz radiation from cesium and rubidium vapor plasma. By taking advantage of the very low ionization potential of cesium (3.89 eV) and rubidium (4.18 eV), we are able to produce a THz wave with an amplitude more than 8 times higher than nitrogen gas at the same pressure, showing the promise of using cesium/rubidium vapor for potential THz photonic applications. Our demonstration now opens the door towards THz air photonics based upon metallic vapors.

Author(s):
Xuan Sun - the Institute of Optics University of Rochester
X.-C. Zhang - the Institute of Optics University of Rochester
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