2. Articole
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Item LUMINESCENT PROPERTIES OF LOW-DIMENSIONAL ZnO:Ag POWDERS OBTAINED BY CHEMICAL DEPOSITION FROM AQUEOUS SOLUTION(2023) Goglidze, Tatiana; Goncearenco, Evghenii; Dementiev, Igor; Nedeoglo, Natalia; Iurieva, Tatiana; Nedeoglo, DumitruPhotoluminescence (PL) spectra of ZnO:Ag highly dispersed powders obtained by chemical deposition from aqueous solution are investigated in the wavelength range between 360 and 750 nm at room temperature under excitation between 250 and 350 nm. Before starting the synthesis, the Ag dopant was introduced into the initial solution in the form of AgNO3 silver nitrate in the amount of 12, 102, and 252 mg. The PL spectra consist of an ultraviolet emission (380 nm) attributed to AgZn acceptor-bound exciton, a short-wavelength violet emission (400 –450 nm) and a wide long-wavelength yellow-orange emission (560 – 600 nm). With decreasing excitation energy, the violet emission decreases in intensity, while the yellow-orange emission increases. This is caused by the phenomenon of self-absorption of the short-wavelength emission and energy transmission to the centers of the long-wavelength emission. A rapid decrease in intensity of all the PL bands is found for the sample with maximum Ag concentration. This fact is due to the appearance of the second phase in the form of silver oxide and, consequently, a decrease in the concentration of AgZn point defects responsible for the bands.Item PROPRIETATILE ELECTRONICE A SUPRAFETEI STRATURILOR DE CdS DEPUSE PE SUPORTURI DE ZnO ȘI SnO2(CEP USM, 2024) Rotaru, CorneliuElectronic properties of the CdS thin films deposited by Close-Spaced Sublimation have been investigated by Kelvin Probe (KP) and Photoelectron Yield Spectroscopy (PYS). The Fermi level position changes between 180 meV and 320 meV below the conduction band minimum for the CdS/AZO heterojunction while the CdS thin films on SnO2 substrates show degeneration. An influence of the technology aspects on the energetic structure of the CdS nanolayer is shown.Item GROWTH OF P-GAN ON SILICON SUBSTRATES WITH ZNO BUFFER LAYERS(Springer Nature, 2020) Raevschi, Simion; Gorceac, Leonid; Botnariuc, Vasile; Branişte, TudorGaN layers on Silicon with ZnO intermediate layer were synthesized by using the HVPE (Hydride Vapor Phase Epitaxy) method. ZnO layers were deposited from solutions of zinc compounds in ethanol or water in two steps. At the first step a ZnO nucleation layer was deposited from a solution of zinc acetate in ethanol, at the second step a ZnO precipitate was deposited from a solution of zinc nitrate and KOH in water by boiling. On the obtained structures the GaN nucleation layers were deposited at 500 ℃ for 15 min, then GaN layers were grown at 850–970 ℃ for 30 ± 5 min. Structures were studied by using the optical and SEM microscope and XRD method. The type of conductivity of the layers was determined by using the method of thermal electromotive force measurement (TEFM). The possibility of the electrical conductivity (EC) type changing from n- to p-type for the GaN layers deposited on silicon substrates with the use of intermediate ZnO layer deposited from solutions is demonstrated for the first time.Item ИЗЛУЧАТЕЛЬНЫЕ СВОЙСТВА ПОРОШКОВ ZnO:Ag, ПОЛУЧЕННЫХ ХИМИЧЕСКИМ ОСАЖДЕНИЕМ ИЗ ВОДНОГО РАСТВОРА(CEP USM, 2020) Гоглидзе, Татьяна; Гончаренко, Евгений; Дементьев, Игорь; Недеогло, Наталья; Юрьева, Татьяна; Недеогло, ДмитрийItem ZnO FOR INFRARED AND TERAHERTZ APPLICATIONS(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.Item THE PHOTOPHYSICAL PROPERTIES OF Ga DOPED ZnO THIN FILMS GROWN BY SPRAY PYROLYSIS METHOD(Springer Nature, 2020) Worasawat, Suchada; Taku, Miyake; Potlog, Tamara; Mimura, HidenoriIn this paper we report nanocrystalline ZnO thin films deposited by varying the Ga concentrations and atmosphere gas, onto the glass substrates using spray pyrolysis technique at 450 °C substrate temperature. After deposition Ga-doped ZnO thin films were annealed at temperature 420 °C in vacuum. The morphological, structural, optical and spectral properties of synthetized thin films have been characterized by scanning electron microscopy, X-ray diffraction, Raman analysis, UV–Vis spectrophotometry and spectrofluorimetry. The XRD result shows hexagonal structure with preferential orientation along the (0002) plane and the dependence of the values of the full-width at half-maximum of this peak on the nature of the gas used in the synthesis. Also, it is found that the optical bandgap can be increased by increasing the doping level. The fluorescence spectra of ZnO thin films with 1%, 2%, 3% and 5% concentrations of Ga demonstrate that these nanostructured thin films can produce reactive oxygen species (ROS) such as singlet oxygen under ultraviolet light. Nanocrystalline ZnO thin films in function of the Ga concentration provide the phosphorescence lifetime of the charge separated states up to 102 ms.Item INFLUENȚA DOPĂRII CU ALUMINIU ASUPRA PROPRIETĂȚILOR OPTICE ALE STRATURILOR SUBȚIRI DE ZnO(CEP USM, 2020) Lungu, IonStraturile nanostructurate ZnO au fost sintetizate din soluții chimice prin metoda pirolizei pulverizate. Prin analiza difracției cu raze X (XRD) și a spectroscopiei UV-Vi sau fost studiate efectele variației concentrației de aluminiu asupra proprietăților optice ale straturilor nanostructurate de ZnO. Concentrația aluminiului în soluția inițială a fost fixată la 0, 1, 2, 3 și 5%.Analiza difracției cu raze X (XRD) confirmă că d oparea cu 1% de aluminiu, în comparație cu celelalte concentrații, îmbunătățește structura cristalină. Cu creșterea concentrației de aluminiu dimensiunea cristalitelor se micșorează. Studiul spectroscopiei UV-Vis a straturilor subțiri indică o transmitanță sporită (~90%) în regiunea vizibilă a spectrului energetic cu lărgimea benzii interzise de 3,23 eV pentru ZnO nedopat și de 3,32 eV pentru ZnO dopat cu Al, care este aproape de valoarea „bulk” a ZnO (3,36 eV).Item PROPRIETĂȚILE FIZICE ALE STRATURILOR DE ZnO PREPARATE PE Si PRIN METODA HIDROTERMALĂ(CEP USM, 2020) Raevschi, Simion; Gorceac, Leonid; Botnariuc, Vasile; Braniște, Tudor; Vatavu, SergiuStraturi subțiri, de nucleație și proprii, de ZnO au fost sintetizate pe Si prin metoda hidrotermală din soluțiile compușilor zincului folosindu-se solvenții: apă, apă + etanol, apă + metanol, apă + propanol, apă + acetonă, etanol, propanol, metanol.La prepararea straturilor de nucleație s-a folosit acetatul de zinc dihidrat, Zn(CH3COO)2·2H2O. Depunerea straturilor proprii de ZnO pe structurile nucleatea avut loc prin fierberea lor în soluție apoasă de Zn(NO 3)2+ KOH. În lucrare sunt date caracterizări structurale și morfologice ale straturilor buffer obținute,fiind demonstrată eficiența stratului buffer în prepararea straturilor de GaN.