Facultatea de Fizică şi Inginerie / Faculty of Physics and Engineering
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Item Recent advances in ZnSe-based devices: from UV to terahertz applications [Articol](CEP USM, 2024) Sirkeli, Vadim P.; Nedeoglo, Natalia D; Nedeoglo, Dmitrii D.; Vatavu, Sergiu A.; Yilmazoglu, Oktay; Hajo, Ahid S.; Preu, Sascha; Hartnagel, Hans L.; Küppers, FrankoZinc selenide is a II-VI compound material with wide bandgap. Due to its unique properties like direct wide bandgap, high resistance to intense UV and X-Ray radiation, ZnSe is attractive material for fabrication of many photonic and electronic devices. In this paper we report on recent advances on ZnSe-based optoelectronic devices covering spectral region from ultraviolet to terahertz.Item ZnO-based terahertz quantum cascade lasers [Articol](Elsevier, 2019) Sirkeli, Vadim; Hartnagel, HansHigh-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.Item Recent advances in Terahertz technology for security and biomedical applications [Articol](Universitatea de Stat din Tiraspol, 2021) Sirkeli, VadimTerahertz 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.Item ZnO for infrared and terahertz applications [Articol](Elsevier, 2021) Sirkeli, Vadim; Hartnagel, HansThis 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.