scholarly journals Terahertz Spectroscopy of Thermal Radiation from AlGaN/GaN Heterostructure on Sapphire at Low Temperatures

2020 ◽  
Vol 10 (3) ◽  
pp. 851 ◽  
Author(s):  
Ignas Grigelionis ◽  
Irmantas Kašalynas
Keyword(s):  
Thermal Radiation ◽  
Sapphire Substrate ◽  
Radiative Decay ◽  
Thermal Emission ◽  
Terahertz Spectroscopy ◽  
Longitudinal Optical ◽  
Thz Spectroscopy ◽  
Electron Transitions ◽  
Shallow Impurities ◽  
Gan Heterostructure

Terahertz spectroscopy of thermal radiation from electrically pumped AlGaN/GaN structures on sapphire substrate was investigated in this work. Comparison of experimental THz spectroscopy results to theoretical spectra calculations shows that thermal radiation of the sample lattice is the main mechanism causing the emission above T = 155 K, and it is mainly influenced by sapphire substrate. Here, the emission was attributed to the radiative electron transitions in shallow impurities and nitrogen vacancies as well as to radiative decay of longitudinal optical phonons (387 cm - 1 ) in sapphire substrate. We have successfully demonstrated that THz emission spectroscopy can be used to define the temperature at which thermal emission from AlGaN/GaN HEMT structures dominates the emission spectrum.

scholarly journals Temperature dependent poly(L-lactide) crystallization investigated by Fourier transform terahertz spectroscopy

2021 ◽  
Author(s):  
Seiichiro Ariyoshi ◽  
Satoshi Ohnishi ◽  
Hikaru Mikami ◽  
Hideto Tsuji ◽  
Yuki Arakawa ◽  
...  
Keyword(s):  
Fourier Transform ◽  
Absorption Spectra ◽  
Terahertz Spectroscopy ◽  
Thz Spectroscopy ◽  
Frequency Range ◽  
Temperature Dependent ◽  
Thz Absorption

Poly(L-lactide) (PLLA) was investigated by Fourier transform terahertz (THz) spectroscopy over the frequency range of 1.0 – 8.5 THz. THz absorption spectra were acquired for PLLA samples isothermally crystallized at...

High-Precision Continuous-Wave Terahertz Spectroscopy Based on a Photomixing Technique for Identifying Pearls

2019 ◽  
Vol 73 (12) ◽  
pp. 1388-1393
Author(s):  
Chihoon Kim ◽  
Taeksoo Ji
Keyword(s):  
Optical Coherence Tomography ◽  
Fourier Transform ◽  
Ir Spectroscopy ◽  
Continuous Wave ◽  
Terahertz Spectroscopy ◽  
Thz Spectroscopy ◽  
Ft Ir ◽  
Thz Absorption ◽  
Ft Ir Spectroscopy ◽  
Cultured Pearls

We present the accurate terahertz spectra of between imitation and cultured pearls using continuous-wave terahertz (CW-THz) spectroscopy. Using Fourier transform infrared (FT-IR) spectroscopy and optical coherence tomography (OCT) measurements, cultured pearls can be distinguished from imitation pearls by observing distinct absorption peaks and discriminative boundaries. The THz absorption spectra up to 0.3 THz obtained from CW-THz spectroscopy show several absorption peaks at specific frequencies with the cultured pearls but no peaks with the imitation pearls, which results from the existence of the nacre polymorph of cultured pearls. Hence, it is expected that the CW-THz system proposed herein will be applicable to fast, nondestructive spectrum analysis including pearl identification.

scholarly journals Terahertz Spectroscopy of Gas Absorption Using the Superconducting Flux-Flow Oscillator as an Active Source and the Superconducting Integrated Receiver

Sensors ◽  
2020 ◽  
Vol 20 (24) ◽  
pp. 7267
Author(s):  
Nickolay V. Kinev ◽  
Kirill I. Rudakov ◽  
Lyudmila V. Filippenko ◽  
Andrey M. Baryshev ◽  
Valery P. Koshelets
Keyword(s):  
Open Space ◽  
Terahertz Spectroscopy ◽  
Near Field ◽  
Gas Absorption ◽  
Thz Spectroscopy ◽  
Single Chip ◽  
Flux Flow ◽  
Practical Applications ◽  
Active Source ◽  
Integrated Receiver

We report on the first implementation of a terahertz (THz) source based on a Josephson flux-flow oscillator (FFO) that radiates to open space. The excellent performance of this source and its maturity for practical applications has been demonstrated by the spectroscopy of gas absorption. To study the radiated power, we used a bolometric detection method and additionally calibrated the power by means of pumping the superconductor–insulator–superconductor (SIS) junction, integrated on a single chip with the FFO. For calibration, we developed a program using the SIS-detected power calculations in accordance with the Tien and Gordon model. The power emitted to open space is estimated to be from fractions of µW to several µW in the wide region from 0.25 THz up to 0.75 THz for different designs, with a maximum power of 3.3 µW at 0.34 THz. Next, we used a gas cell and a heterodyne superconducting integrated receiver to trace the absorption lines of water and ammonia with a spectral resolution better than 100 kHz. Our experiment for gas absorption is the first demonstration of the applicability of the FFO as an external active source for different tasks, such as THz spectroscopy, near-field THz imaging and microscopy.

Improved carrier mobility of InAlN/GaN heterostructure grown on cone-shaped patterned sapphire substrate

2014 ◽  
Vol 53 (11) ◽  
pp. 110314 ◽  
Author(s):  
Yi Zhao ◽  
JinCheng Zhang ◽  
JunShuai Xue ◽  
ShengRui Xu ◽  
XiaoWei Zhou ◽  
...  
Keyword(s):  
Sapphire Substrate ◽  
Carrier Mobility ◽  
Patterned Sapphire Substrate ◽  
Gan Heterostructure

Exciton Spectra of AlN Epitaxial Films

2001 ◽  
Vol 693 ◽  
Author(s):  
T. Onuma ◽  
S. F. Chichibu ◽  
T. Sota ◽  
K. Asai ◽  
S. Sumiya ◽  
...  
Keyword(s):  
Sapphire Substrate ◽  
Characteristic Temperature ◽  
Longitudinal Optical ◽  
Epitaxial Films ◽  
Longitudinal Optical Phonon ◽  
Bohr Radius ◽  
Spectral Lineshape ◽  
Resonance Energies ◽  
Excitonic Emission ◽  
Excitonic Resonance

AbstractExcitonic resonance energies in a C-plane AlN epilayer on the (0001) sapphire substrate grown by low-pressure metalorganic vapor phase epitaxy were determined as a function of temperature by means of optical reflectance (OR) and cathodoluminescence (CL) measurements. The OR spectra exhibited distinct reflectance anomalies at the photon energies just above the multiple internal reflection fringes, and the spectral lineshape was fitted considering A (???u7v7c) and BC (???9v,???17v7c) exciton transitions. The energies of them at 0 K were obtained to be 6.211 and 6.266 eV, giving the crystal field splitting (Δcr) of approximately 55 meV. The AlNfilm exhibited an excitonic emission even at 300 K, which is due to the small Bohr radius of excitons and large longitudinal optical phonon energies. The Einstein characteristic temperature Q E was estimated to be 580 K.

scholarly journals Diffuse terahertz spectroscopy in turbid media using a wavelet-based bimodality spectral analysis

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Mahmoud E. Khani ◽  
Omar B. Osman ◽  
M. Hassan Arbab
Keyword(s):  
Electromagnetic Scattering ◽  
Terahertz Spectroscopy ◽  
A Priori ◽  
Incident Beam ◽  
Mie Scattering ◽  
Turbid Media ◽  
Thz Spectroscopy ◽  
Receiver Operating Characteristic Curves ◽  
Wavelet Multiresolution Analysis ◽  
Priori Information

AbstractCurrent terahertz (THz) spectroscopy techniques only use the coherent light beam for spectral imaging. In the presence of electromagnetic scattering, however, the scattering-mitigated incoherent beams allow for flexible emitter-detector geometries, which enable applications such as seeing through turbid media. Despite this potential, THz spectroscopy using diffuse waves has not been demonstrated. The main obstacles are the very poor signal to noise ratios of the diffused fields and the resonance-like spectral artifacts due to multiple Mie scattering events that obscure the material absorption signatures. In this work, we demonstrate diffuse THz spectroscopy of a heterogeneous sample through turbid media using a novel technique based on the wavelet multiresolution analysis and the bimodality coefficient spectrum, which we define here for the first time using the skewness and kurtosis of the spectral images. The proposed method yields broadband and simultaneous material characterization at detection angles as high as 90° with respect to the incident beam. We determined the accuracy of the wavelet-based diffuse spectroscopy at oblique detection angles, by evaluating the area under the receiver operating characteristic curves, to be higher than 95%. This technique is agnostic to any a priori information on the spectral signatures of the sample materials or the characteristics of the scattering medium, and can be expanded for other broadband spectroscopic modalities.

Demonstration of undoped quaternary AlInGaN∕GaN heterostructure field-effect transistor on sapphire substrate

2005 ◽  
Vol 86 (22) ◽  
pp. 223510 ◽  
Author(s):  
Y. Liu ◽  
H. Jiang ◽  
S. Arulkumaran ◽  
T. Egawa ◽  
B. Zhang ◽  
...  
Keyword(s):  
Sapphire Substrate ◽  
Field Effect ◽  
Field Effect Transistor ◽  
Effect Transistor ◽  
Gan Heterostructure

scholarly journals Broadband Terahertz Spectroscopy of Phonon-Polariton Dispersion in Ferroelectrics

Photonics ◽  
2018 ◽  
Vol 5 (4) ◽  
pp. 55 ◽  
Author(s):  
Seiji Kojima
Keyword(s):  
Electromagnetic Waves ◽  
Terahertz Spectroscopy ◽  
Far Infrared ◽  
Longitudinal Optical ◽  
Vibrational Modes ◽  
Terahertz Time Domain Spectroscopy ◽  
Raman Scattering Spectroscopy ◽  
Longitudinal Optical Mode ◽  
Relationship Of ◽  
The Relationship

Electromagnetic waves at frequencies below the X-ray region strongly couple to the optical vibrational modes in a solid. These coupled excitations have been called phonon polaritons. The relationship of the polariton frequency versus the polariton wavevector shows a remarkable dispersion, especially in the vicinity of the transverse and longitudinal optical mode frequencies. The significant frequency dependence enables valuable applications such as a tunable terahertz radiation source. The polariton dispersion relations of technologically important dielectric and ferroelectric crystals were reviewed in the broad terahertz range using terahertz time-domain spectroscopy, far-infrared spectroscopy, and Raman scattering spectroscopy.

scholarly journals Non-thermal emission from cosmic rays accelerated in H II regions

2019 ◽  
Vol 630 ◽  
pp. A72 ◽  
Author(s):  
Marco Padovani ◽  
Alexandre Marcowith ◽  
Álvaro Sánchez-Monge ◽  
Fanyi Meng ◽  
Peter Schilke
Keyword(s):  
Cosmic Rays ◽  
Thermal Radiation ◽  
Thermal Emission ◽  
Cosmic Ray ◽  
Local Source ◽  
Relativistic Electrons ◽  
Deep South ◽  
Fermi Acceleration ◽  
First Order ◽  
Order Of Magnitude

Context. Radio observations at metre-centimetre wavelengths shed light on the nature of the emission of H II regions. Usually this category of objects is dominated by thermal radiation produced by ionised hydrogen, namely protons and electrons. However, a number of observational studies have revealed the existence of H II regions with a mixture of thermal and non-thermal radiation. The latter represents a clue as to the presence of relativistic electrons. However, neither the interstellar cosmic-ray electron flux nor the flux of secondary electrons, produced by primary cosmic rays through ionisation processes, is high enough to explain the observed flux densities. Aims. We investigate the possibility of accelerating local thermal electrons up to relativistic energies in H II region shocks. Methods. We assumed that relativistic electrons can be accelerated through the first-order Fermi acceleration mechanism and we estimated the emerging electron fluxes, the corresponding flux densities, and the spectral indexes. Results. We find flux densities of the same order of magnitude of those observed. In particular, we applied our model to the “deep south” (DS) region of Sagittarius B2 and we succeeded in reproducing the observed flux densities with an accuracy of less than 20% as well as the spectral indexes. The model also gives constraints on magnetic field strength (0.3–4 mG), density (1–9 × 104 cm−3), and flow velocity in the shock reference frame (33–50 km s−1) expected in DS. Conclusions. We suggest a mechanism able to accelerate thermal electrons inside H II regions through the first-order Fermi acceleration. The existence of a local source of relativistic electrons can explain the origin of both the observed non-thermal emission and the corresponding spectral indexes.

Sign in / Sign up

Export Citation Format

Share Document