Terahertz Modulation of Hexagonal-Shaped Metamaterials Employing ZnO Quantum Dots (original) (raw)
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Active terahertz metamaterials
Optics and Spectroscopy, 2010
In this paper we present an overview of research in our group in terahertz (THz) metamaterials and their applications. We have developed a series of planar metamaterials operating at THz frequencies, all of which exhibit a strong resonant response. By incorporating natural materials, e.g., semiconductors, as the substrates or as critical regions of metamaterial elements, we are able to effectively control the metamaterial resonance by the application of external stimuli, e.g., photoexcitation and electrical bias. Such actively con trollable metamaterials provide novel functionalities for solid state device applications with unprecedented performance, such as THz spectroscopy, imaging, and many others.
Study on Active Terahertz Metamaterials
Background: "Metamaterial" is defined as an artificially structured electromagnetic material exhibiting extraordinary response to the electromagnetic radiation that is hardly performed in natural fashions. Study on "metamaterial" is now one of the emerging science and engineering fields . "Terahertz (THz)" stayrtzing in between radio and optical frequencies is still an unexplored, but now becoming one of the hottest frequency bands [4] to creating new "active" metamaterial systems . In [5], Chen et al., first demonstrated an "active" transmittance control by 50% of THz radiation by implementing an arrayed semiconductor metamaterial structure including Schottky diodes. This is an excellent first-step ignition, but fundamental improvements/breakthroughs are necessary to explore deeper science and technology hidden behind the presence. On such a background, two dimensional plasmons (2DPs) in submicron transistors have attracted much attention due to their nature of promoting emission/detection/manipulation of electromagnetic radiation in the THz range . In 2009 FSY under the AOARD Grant 09-4013, the grantee investigated THz radiation sources and modulators formed by active metamaterials made with the grantee's original interdigitated grating gate (DGG) structures on 2DP-HEMT device layers . The grantee continues the research as the follow-on work, consisting of the following two subjects: 1) completion of the verification and enhancement of the coherent monochromatic emission from the high-Q cavity DGG-HEMT, and 2) experimental verification of plasmon-resonant-type THz intensity modulation.
THz Metamaterial Characterization Using THz-TDS
Terahertz Spectroscopy - A Cutting Edge Technology, 2017
The purpose of this chapter is to familiarize the reader with metamaterials and describe terahertz (THz) spectroscopy within metamaterials research. The introduction provides key background information on metamaterials, describes their history and their unique properties. These properties include negative refraction, backwards phase propagation, and the reversed Doppler Effect. The history and theory of metamaterials are discussed, starting with Veselago's negative index materials work and Pendry's publications on physical realization of metamaterials. The next sections cover measurement and analyses of THz metamaterials. THz Time-domain spectroscopy (THz-TDS) will be the key measurement tool used to describe the THz metamaterial measurement process. Sample transmission data from a metamaterial THz-TDS measurement is analyzed to give a better understanding of the different frequency characteristics of metamaterials. The measurement and analysis sections are followed by a section on the fabrication process of metamaterials. After familiarizing the reader with THz metamaterial measurement and fabrication techniques, the final section will provide a review of various methods by which metamaterials are made active and/or tunable. Several novel concepts were demonstrated in recent years to achieve such metamaterials, including photoconductivity, high electron mobility transistor (HEMT), microelectromechanical systems (MEMS), and phase change material (PCM)-based metamaterial structures.
Improvement of Terahertz Photoconductive Antenna using Optical Antenna Array of ZnO Nanorods
Scientific Reports, 2019
An efficient terahertz (THz) photoconductive antenna (PCA), as a major constituent for the generation or detection of THz waves, plays an essential role in bridging microwave-to-photonic gaps. Here, we propose an impressive approach comprising the use of arrayed zinc oxide nanorods (ZnO NRs) as an optical nanoantenna over an anti-reflective layer (silicon nitride) in the antenna gap to boost the photocurrent and consequently the THz signal. The numerical approach applied in investigating the optical behavior of the structure, demonstrates a significant field enhancement within the LT-GaAs layer due to the optical antenna performing simultaneously as a concentrator and an antireflector which behaves as a graded-refractive index layer. ZnO NRs have been fabricated on the PCA gap using the hydrothermal method as a simple, low cost and production compatible fabrication method compared to other complex methods used for the optical nanoantennas. Compared to the conventional PCA with a tra...
Applied Physics Letters, 2005
Terahertz ͑THz͒ radiation generated from photoconductive antenna fabricated on a single crystal zinc oxide ͑ZnO͒ is presented. The THz-radiation power is saturated at bias voltages above 800 V / cm and the obtained spectrum extends up to 1 THz. Moreover, ZnO is found to be highly transparent in the visible, near-infrared, mid-infrared and THz frequency regions. The results depicted here will categorically unravel the prospects of using ZnO as a material for integrated active optics.
Dynamically reconfigurable terahertz metamaterial through photo-doped semiconductor
Applied Physics Letters, 2011
Broadband polarization transformation via enhanced asymmetric transmission through arrays of twisted complementary split-ring resonators Appl. Phys. Lett. 99, 221907 Multi-beam generations at pre-designed directions based on anisotropic zero-index metamaterials Appl. Phys. Lett. 99, 131913 Reconfigurable gradient index using VO2 memory metamaterials Appl. Phys. Lett. 99, 044103 Equivalent circuit method analysis of the influence of frequency selective surface resistance on the frequency response of metamaterial absorbers J. Appl. Phys. 110, 023704 Ultrathin multiband gigahertz metamaterial absorbers
Efficient Control of THz Transmission of PEDOT:PSS with Resonant Nano-Metamaterials
Scientific Reports
Nano-metamaterials designed to operate at a certain resonance frequency enhance the magnitude of terahertz (THz) wave transmission by three orders of magnitude or even more. In this pursuit, controlling magnitude of resonant transmission and tuning the resonance frequency is increasingly important for application in low power THz electronics and devices. THz optical properties of chemically doped poly(3,4‐ethylenedioxythiophene):poly(4‐styrenesulfonate) (PEDOT:PSS) have been studied, however its effect on the THz transmission properties in combination with nano-metamaterials have not yet been demonstrated. Here we demonstrate the efficient control over resonant THz transmission and tuning of resonance frequency of different nano-metamaterials using PEDOT:PSS, without any toxic chemical doping. By ease of simple solution processing with single step and drop-casting 10 μL aqueous solution of PEDOT:PSS on different nano-metamaterials with varied concentrations, we were able to dynamica...
Performance enhancement of terahertz metamaterials on ultrathin substrates for sensing applications
Applied Physics Letters, 2010
We design, fabricate, and characterize split-ring resonator ͑SRR͒ based planar terahertz metamaterials ͑MMs͒ on ultrathin silicon nitride substrates for biosensing applications. Proof-of-principle demonstration of increased sensitivity in thin substrate SRR-MMs is shown by detection of doped and undoped protein thin films ͑silk fibroin͒ of various thicknesses and by monitoring transmission changes using terahertz time-domain spectroscopy. SRR-MMs fabricated on thin film substrates show significantly better performance than identical SRR-MMs fabricated on bulk silicon substrates paving the way for improved biological and chemical sensing applications.
Experimental study of terahertz emission from ZnSe and ZnTe nano structures
2008
Terahertz (THz) emission from ZnSe and ZnTe nano dots and nano gratings is experimentally studied compared with that from <111> orientation bulk ZnSe and <110> orientation bulk ZnTe. These nano dots and nano gratings are fabricated by the femtosecond laser ablation technique. Three main mechanisms coexist in the THz radiation from ZnSe and ZnTe surface nano structures as the same as from bulk sample: current surge effect (drift current), Photo Dember effect (diffusion current), and optical rectification. Moreover, it is found that nano structures not only contribute to an enhancement of THz emission, but also increase the threshold of polarity reversal of THz wave, and widen the spectrum of THz radiation. We also observe a two-fold symmetry in rotating pump polarization angle from ZnTe nano gratings, which is completely different from the three-fold symmetry observed from bulk ZnTe.