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Item 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 roomItem THE USE OF METAL OXIDE SEMICONDUCTORS FOR THZ SPECTROSCOPY OF BIOLOGICAL APPLICATIONS(Springer Nature, 2019) Hartnagel, Hans Ludwig; Sirkeli, VadimTerahertz (THz) waves refer to the electromagnetic radiation in the frequency range from 0.1 to 10 THz, which corresponds to the wavelengths from 3 mm to 30 µm, respectively. This spectral region, called also as “T-gap”, is important for many practical applications, including THz imaging, chemical and biological sensing, high-speed telecommunication, security and medical applications. 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 neither ignite any explosive materials at typical power levels nor cause any harmful ionization in biological tissues. The terahertz radiation is strongly attenuated by water and is very sensitive to water content. Unique THz absorption spectra caused by intermolecular vibrations in this spectral region have been found in different biological materials and tissues. Thus, Terahertz spectroscopy provides a powerful tool for characterization of a great many bio molecules and tissues. All these applications require relatively high power terahertz sources with milliwatt-level output power, which could operate at room temperature. Despite great progress, made in the last few years of design, fabrication and demonstration, THz devices based on GaAs/AlGaAs materials, there are some limits of bandgap engineering due to the relatively low (0.72 eV for GaAs/AlAs) conduction band offset, and most terahertz sources with one milliwatt-power like quantum cascade lasers (QCLs) require cryogenic cooling down to less than 200 K. To overcome the issue the new material systems such as metal oxide materials are considered as promising for room-temperature THz sources. The interest in terahertz imaging and spectroscopy of biologically related applications is increasing more and more within the last few years. This paper provides a review and current status of using metal oxide materials for THz spectroscopy, and recent advances in terahertz spectroscopy techniques in biological and medical applications.Item STRUCTURE AND OPTICAL PROPERTIES OF GaSe-CdSe COMPOSITES DRIVEN BY Cd INTERCALATION IN GaSe LAMELLAR CRYSTALS(2015) Caraman, Iuliana; Kantser, Valeriu; Evtodiev, Igor; Leontie, Liviu; Arzumanyan, Grigory; Untila, Dumitru; Dmitroglo, LilianaA new composite material composed of GaSe and CdSe has been obtained by treatment of GaSe single-crystal lamellas in Cd vapors at temperatures of 773853 K and intercalation of Cd interlayers. The structure and optical properties of the GaSe-CdSe composite material have been studied. The content of CdSe crystallites was found to grow with increasing treatment temperature or with increasing duration of treatment at a constant temperature. Analysis of XRD, PL, XPS, AFM, and Raman patterns has shown that the heterogeneous composite composed of micro and nanocrystallites of CdSe in GaSe can be obtained by Cd intercalation in a temperature range of 753853 K. On the basis of Raman spectrum, the vibrational modes of the composite have been identified. The PL of these materials contains emission bands of free and bound excitons, donor-acceptor bands, and bands of recombination via impurity levels. The PL emission spectra measured at a temperature of 78 and 300 K for the composites result from the overlapping of the emission bands of the components of GaSe doped with Cd and the CdSe crystallites.Item STRUCTURAL AND OPTICAL PROPERTIES OF COMPOSITES CONTAINING A III B VI AND A II B VI SEMICONDUCTORS(2017) Evtodiev, Igor; Untila, Dumitru; Evtodiev, Silvia; Caraman, Iuliana; Gasin, Petru; Dmitroglo, Liliana; Rotaru, Irina; Kantser, ValeriuBy thermal annealing of InSe, GaSe, and GaTe crystals in Zn vapors at 800, 870, and 1050K, respectively, a material consisting of ZnSe crystallites in both GaSe and InSe and ZnTe in GaTe has been prepared. Structural defects induced by intercalated atoms shield excitonic bonds in primary compounds and form both radiative recombination levels and electron trapping levels localized deep in the band gap of AIIIBVI crystals. The energies of trapping levels have been determined from thermally stimulated luminescence curves.