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Subject: search.filters.subject.terahertz (THz) radiation

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Now showing 1 - 9 of 9
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    RECENT PROGRESS IN GaN-BASED DEVICES FOR TERAHERTZ TECHNOLOGY
    (Springer Nature, 2020) Sirkeli, Vadim; Tiginyanu, Ion; Hartnagel, Hans
    This paper reviews the crystal growth, basic properties, and principle of operation of III-nitride based terahertz devices. We provide a brief history and current status of crystal growth of polar and non-polar GaN-based heterostructures and its properties. The role of spontaneous and piezoelectric polarization in polar III-nitride structures and its impact on performance of terahertz devices is discussed in detail. We show that GaN-based semiconductor compounds are promising materials for fabrication terahertz sources operating up to room temperature due to their unique properties such as large bandgap and conduction band offset (CBO) energy, high LO-phonon energy, and high resistant to the high breakdown electric field. Moreover, it was established that the GaN-based terahertz sources can cover the spectral region of 5–12 THz, which is very important for THz imaging and detection of explosive materials, and which could be not covered by conventional GaAs-based terahertz devices. In terms of the reported significant progress in growth of non-polar m-plane GaN-based heterostructures and devices with low density defects, it is open a wide perspective towards design and fabrication of non-polar m-plane GaN-based high power terahertz sources with capabilities of operation at room temperature.
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    ZnO-BASED QUANTUM STRUCTURES FOR TERAHERTZ SOURCES
    (Springer Nature, 2020) Sirkeli, Vadim; Hartnagel, Hans; Yilmazoglu, O.; Preu, S.
    In this paper we report on the numerical study of the terahertz devices based on metal oxide semiconductors and its application in biology and medicine. We also report on the recent progress of the theoretical and experimental studies of ZnO-based THz quantum cascade lasers (QCLs) and resonant tunneling diodes (RTDs). We show that ZnO-based semiconductor compounds are promising materials for fabrication terahertz sources operating up to room temperature due to their unique properties such as large bandgap and conduction band offset (CBO) energy, high LO-phonon energy, and high resistant to the high breakdown electric field. Moreover, it was established that the ZnO-based terahertz sources can cover the spectral region of 5–12 THz, which is very important for THz imaging and detection of explosive materials, and which could be not covered by conventional GaAs-based terahertz devices. In terms of the reported significant progress in growth of non-polar m-plane ZnO-based heterostructures and devices with low density defects, it is open a wide perspective towards design and fabrication of non-polar m-plane ZnO-based high power terahertz sources with capabilities of operation at room
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    ZnO-BASED TERAHERTZ QUANTUM CASCADE LASERS
    (Elsevier, 2019) Sirkeli, Vadim; Hartnagel, Hans
    High-power terahertz sources operating at room-temperature are promising for many applications such as explosive materials detection, non-invasive medical imaging, and high speed telecommunication. Here we report the results of a simulation study, which shows the significantly improved performance of room-temperature terahertz quantum cascade lasers (THz QCLs) based on a ZnMgO/ZnO material system employing a 2-well design scheme with variable barrier heights and a delta-doped injector well. We found that by varying and optimizing constituent layer widths and doping level of the injector well, high power performance of THz QCLs can be achieved at room temperature: optical gain and radiation frequency is varied from 108 cm−1 @ 2.18 THz to 300 cm−1 @ 4.96 THz. These results show that among II–VI compounds the ZnMgO/ZnO material system is optimally suited for high-performance room-temperature THz QCLs.
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    RECENT ADVANCES IN TERAHERTZ TECHNOLOGY FOR SECURITY AND BIOMEDICAL APPLICATIONS
    (Universitatea de Stat din Tiraspol, 2021) Sirkeli, Vadim
    Terahertz waves have low photon energies (~ 4.1 meV for 1 THz), which is about 1 million times weaker than the energy of X-ray photons. They do not cause any harmful ionization in biological tissues. The terahertz radiation is strongly attenuated by water and is very sensitive to water content. This paper provides current status and recent advances in terahertz technology for security and medical applications. In particular, we report on our designs of THz quantum cascade lasers to identify cancerous tissues and other medical issues.
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    THZ SPECTROSCOPY BY NARROW SPECTRAL EMISSION OF QUANTUM CASCADE LASERS FOR MEDICAL APPLICATIONS
    (Institute of Electrical and Electronics Engineers, 2021) Hartnagel, Hans; Sirkeli, Vadim; Acedo, Pablo
    THz waves have low photon energies (~ 4.1 meV for 1 THz), which is about 1 million times weaker than the energy of X-ray photons. They do not cause any harmful ionization in biological tissues. The terahertz radiation is strongly attenuated by water and is very sensitive to water content. The interest in terahertz imaging and spectroscopy of biologically related applications is increasing. This paper provides current status and recent advances in terahertz spectroscopy techniques in biological and medical applications. In particular, we report on our designs of THz Quantum-Cascade sources to identify cancerous tissues and other medical issues.
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    ZnO FOR INFRARED AND TERAHERTZ APPLICATIONS
    (Elsevier, 2021) Sirkeli, Vadim; Hartnagel, Hans
    This chapter reviews the recent progress of the theoretical and experimental studies of ZnO-based structures such as quantum cascade lasers, resonant-tunneling diodes, and quantum well detectors and their applications for infrared and terahertz spectral range. The role of spontaneous and piezoelectric polarization in polar ZnO-based structures and their impact on intersubband transitions and the performance of terahertz devices are discussed in detail. It is shown that ZnO-based compounds are promising materials for the fabrication of terahertz sources operating up to room temperature due to their unique properties such as their large bandgap, conduction band offset energy, and high longitudinal-optical phonon energy. Moreover, ZnO-based terahertz sources can cover the spectral region of 0.1–12 THz, which is very important for THz imaging and detection of explosive materials and medical spectroscopy applications, which could be not covered by conventional GaAs-based terahertz devices. In terms of the reported significant progress in the growth of nonpolar m-plane ZnO-based heterostructures and devices with low defect density, a wide perspective for the design and fabrication of high-power terahertz sources at room-temperature operation is now opened up.
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    RESONANT TUNNELING AND QUANTUM CASCADING FOR OPTIMUM ROOM-TEMPERATURE GENERATION OF THz SIGNALS
    (Institute of Electrical and Electronics Engineers, 2017) Sirkeli, Vadim; Yilmazoglu, Oktay
    We report on the results of a numerical study of quantum transport in ZnSe-based resonant-tunneling diodes (RTDs) and quantum cascade oscillators (QCOs) with fixed and unequal barrier heights. It is found that the negative differential resistance exists up to room temperature in the current-voltage characteristics of the RTD and QCO devices with unequal barrier heights. Further, we demonstrate that QCOs with unequal barrier heights have a better frequency and power performance characteristics compared with RTDs and are more beneficial for high-power terahertz generation at room temperature. For the best QCO device with 100 periods of quantum cascading, a maximum output power of ~7-9 μW for the operating frequency range from 0.1 to ~6 THz at room temperature was achieved.
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    PROPOSAL FOR A MONOLITHIC BROADBAND TERAHERTZ QUANTUM CASCADE LASER ARRAY TAILORED TO DETECTION OF EXPLOSIVE MATERIALS
    (American Scientific Publishers, 2018) Sirkeli, Vadim; Yilmazoglu, Oktay
    Since most tunable THz sources produce only small power levels, we propose for routine evaluation of dangerous materials to employ a chain of quantum cascade THz generators, where each of them addresses a specific spectroscopic line of the relevant identifying spectrum. Therefore, we present the design, operating principle and performance of a room-temperature monolithic broadband terahertz (THz) source for applications of THz imaging and detection of explosive materials such as TNT, RDX, PETN and HMX. The suggested terahertz source is a 20-element array of quantum cascade lasers (QCLs) emitting at discrete frequencies from 0.85 to 4.74 THz. The layer structure of each individual THz QCL is based on a two-well design scheme with variable barrier heights and resonant-phonon depopulation of the lower laser state. The tailoring of emission frequency of individual THz QCLs in the laser array was made by varying the constituent epilayers' width and doping level of the injector well. We found that the peak optical gain of the discrete THz QCLs is increased with increasing tailored THz emission frequency. The detection of the transmitted line can be done by THz Schottky diodes after relevant narrow-band filters. The other detector concept could be quantum cascading, where its narrow-band filter property allows the detection of the relevant THz line. This system is intended for routine security testing, where speed and reliability are required.