Browsing by Author "Caraman, Iuliana"

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CARACTERIZAREA STRUCTURALĂ A NANOFORMAȚIUNILOR DE Ga2O3 OBȚINUTE PRIN TRATAMENT TERMIC AL MONOCRISTALELOR Ga2S3
(Universitatea Tehnică din Moldova, 2018-05-24) Untilă, Dumitru; Sprincean, Veaceslav; Caraman, Mihail; Cojocaru, Ala; Lupan, Oleg; Tighineanu, Ion; Palachi, Leonid; Caraman, Iuliana
Prin tratament termic (TT), în atmosferă normală, al monocristalelor β-Ga2S3, cu rețea cristalină monoclinică, la temperaturi din intervalul 970-1170 K, timp de 3-6 ore, suprafața acestora se acoperă cu un strat omogen de β-Ga2O3, cu rețea cristalină monoclinică. La interfața monocristal-oxid se formează nanocristalite de Ga2O3 și Ga2S3. Structura cristalină și dimensiunile medii ale cristalitelor sunt analizate prin măsurări XRD, SEM și Raman.
THE COPPER INFLUENCE ON THE PL SPECTRA OF CDTE THIN FILM AS A COMPONENT OF THE CDS/CDTE HETEROJUNCTION
(Elsevier, 2009) Vatavu, Sergiu; Zhao, Hehong; Caraman, Iuliana; Gașin, Petru; Ferekides, Chris
The influence of annealing in the presence of CdCl2 and a thin copper layer deposited onto CdTe on the photoluminescence spectra of CdTe, as a component of CdS/CdTe heterojunction, has been studied for two excitation wavelengths: 0.337 μm and 0.6328 μm. The behavior of the PL was studied as a function of the measurement temperature and excitation intensity. At 0.6328 μm excitation, the interface PL consists of a known 1.43X band, and the chloride annealing enhances radiative transitions at 1.536 eV. The intensity of the 1.536 eV transitions increases when Cu is present. The PL of as-deposited CdTe films prepared in the presence of oxygen has the 1.45X band attenuated when excited with 0.337 μm excitation wavelength.
CRYSTALLINE STRUCTURE AND PHOTOLUMINESCENCE OF GaSe-CdSe NANOCOMPOSITE
(2015) Dmitroglo, Liliana; Evtodiev, Igor; Caraman, Iuliana; Kantser, Valeriu; Untila, Dumitru; Stamate, Marius; Gasin, Petru
A material consisting of CdSe and GaSe crystallites with average dimensions of 34 nm and 30 nm respectively was obtained by heat treatment at 753K and 853K of GaSe single crystal plates in Cd vapors during 24 hours. As a result of Cd atoms interaction with Se atoms CdSe layers are formed both onto outer surface and at interface of layered Se-Ga-Ga-Se packages. CdSe crystallites on the surface grow in the form of plates along C6 crystallographic axis. Photoluminescence spectra of the composite, at 78K and 300K, contain predominant bands from the luminescent emission of GaSe and CdSe components.
CRYSTALLINE STRUCTURE, SURFACE MORPHOLOGY AND OPTICAL PROPERTIES OF NANOLAMELLAR COMPOSITES OBTAINED BY INTERCALATION OF InSe WITH Cd
(2015) Untila, Dumitru; Caraman, Iuliana; Evtodiev, Igor; Canțer, Valeriu; Spalatu, Nicolae; Leontie, Liviu; Dmitroglo, Liliana; Luchian, Efimia
A material composed of InSe and CdSe crystallites was obtained by heat treatment at 753K of InSe single crystalline plates in Cd vapour for 3÷24 hours. The average diameters of CdSe and InSe crystallites determined from diffraction lines analysis are respectively equal to 20 nm and 22 nm. The photoluminescence spectra at 300K and 80K of composite decompose well into two Gaussian curves, one is in good correlation with the photoluminescence of CdSe crystals and the other is shifted to higher energies than the width of the band gap of CdSe crystals.
CRYSTALLINITY AND OPTICAL PROPERTIES OF β-Ga2O3/Ga2S3 LAYERED STRUCTURE OBTAINED BY THERMAL ANNEALING OF Ga2S3 SEMICONDUCTOR
(2021) Sprincean, Veaceslav; Lupan, Oleg; Caraman, Iuliana; Untila, Dumitru; Postica, Vasile; Cojocaru, Ala; Gapeeva, Anna; Palachi, Leonid; Adeling, Rainer; Tiginyanu, Ion; Caraman, Mihail
In this work, the β-Ga2O3 nanostructures were obtained by thermal annealing in air of β-Ga2S3 single crystals at relatively high temperatures of 970 K, 1070 K and 1170 K for 6 h. The structural, morphological, chemical and optical properties of β-Ga2O3–β-Ga2S3 layered composites grown at different temperatures were investigated by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX) as well as photoluminescence spectroscopy (PL) and Raman spectroscopy. The results show that the properties of obtained β-Ga2O3–β-Ga2S3 composites were strongly influenced by the thermal annealing tem- perature. The XRD and Raman analyses confirmed the high crystalline quality of the formed β-Ga2O3 nano- structures. The absorption edge of the oxide is due to direct optical transitions. The optical bandwidth was estimated to be approximately 4.34-4.41 eV, depending on the annealing temperature. Annealing of the β-Ga2S3 monocrystals at a higher temperature of 1170 K showed the complete conversion of the surface to β-Ga2O3. These results demonstrate the possibility to grow high quality β-Ga2O3–β-Ga2S3 layered composites and β-Ga2O3 nanostructures in large quantities for various applications such as gas sensing, non-toxic biomedical imaging, nonlinear optical, as well as power device applications. Micro and nanocrystallites present on the surface of the Ga2O3 layer contribute to a diffusion of the incident light which leads to an increase of the absorption rate allowing thus to reduce the thickness of the Ga2O3 layer, in which the generation of unbalanced charge carriers takes place. By decreasing the Ga2O3 layer thickness in such layered composites, the efficiency of photovoltaic cells based on such junctions can be increased.
FOTOLUMINESCENŢA STRATURILOR NANOLAMELARE DE GaSe OBŢINUTE PRIN INTERCALAREA CU Cd
(2012) Dmitroglo, Liliana; Evtodiev, Igor; Caraman, Iuliana; Nedeff, Valentin; Dafinei, Adrian
S-au analizat spectrele de emisie fotoluminescentă a lamelor monocristaline p-GaSe cu concentraţia golurilor3•1014 cm-3 şi a lamelor intercalate cu Cd în fază de vapori la temperatura 500 °C. Durata tratamentului termic a fost de 20 şi 24 ore. Spectrul de emisie al cristalelor de GaSe conţine liniile excitonilor direcţi localizaţi cu energia de legătură ~6 meV, prima repetare fononică a acestora (ħωf =20 meV) şi banda de emisie a excitonilor indirecţi cu emisia fononilor cu energia 15 meV. Spectrul de emisie a compozitelor obţinute prin intercalarea lamelor de GaSe cu Cd se obţine în rezultatul suprapunerii benzilor de emisie a compusului CdSe şi banda impuritară a monoseleniurii de galiu. Structura spectrului FL depinde de durata tratamentului termic. La majorarea timpului de tratament se amplifică subbanda corespunzătoare compusului CdSe.
GROWTH AND CHARACTERIZATION OF Eu DOPED GaSe SINGLE CRYSTALS BY X-RAY DIFFRACTION AND RAMAN SPECTROSCOPY
(CEP USM, 2017) Untila, Dumitru; Evtodiev, Igor; Caraman, Iuliana; Kantser, Valeriu; Spalatu, Nicolae; Dmitroglo, Liliana; Evtodiev, Silvia; Spoială, Dorin; Rotaru, Irina; Gașin, Petru
GaSe single crystals doped with Eu (0.025, 0.05, 0.5, 1.0 and 3.0 at%) were grown by Bridgman method using Ga, Se and Eu elementary components. The crystalline structure and vibration modes of the GaSe: Eu crystals lattice were studied by X-ray diffraction and Raman spectroscopy. Eu atoms arranged in the van der Waals space of GaSe: Eu crystals form Eu-Se valence bonds and restructure hexagonal lattice of GaSe leading to EuGa2Se4 crystallites formation. Defects generated by EuGa2Se4 crystallites lead to broadening and shifting of single phonon peaks present in Raman spectra towards shorter wavenumbers, and at the same time, activate the longitudinal optical vibrations of EuSe sublattice.
KINETICS OF PHOTOCONDUCTIVITY AND PHOTOLUMINESCENCE OF CdS/CdTe HETEROJUNCTIONS
(2005) Vatavu, Sergiu; Caraman, Iuliana; Gasin, Petru
The photoluminescence and absoption spectral distribution close to the edge of fundamental band were studied in the CdS and CdTe films components of the CdS/CdTe heterojunctions. Recombination level energetic position was determined. The annealing of the CdS/CdTe heterojunctions in presence of CdCl2 results in formation of new recombination levels, revealed by a luminescent band in the energy range of 1.6-1.7 eV and by the shift of the impurity band maximum to the red wavelength region by 50 meV.
KINETICS OF PHOTOCONDUCTIVITY AND PHOTOLUMINESCENCE OF CdS/CdTe HETEROJUNCTIONS
(2005) Vatavu, Sergiu; Caraman, Iuliana; Gashin, Peter A.
The photoluminescence and absoption spectral distribution close to the edge of fundamental band were studied in the CdS and CdTe films components of the CdS/CdTe heterojunctions. Recombination level energetic position was determined. The annealing of the CdS/CdTe heterojunctions in presence of CdCl2 results in formation of new recombination levels, revealed by a luminescent band in the energy range of 1.6-1.7 eV and by the shift of the impurity band maximum to the red wavelength region by 50 meV.
MORFOLOGIA SUPRAFEŢEI ŞI PROPRIETĂŢILE OPTICE ŞI FOTOELECTRICE ALE HETEROJONCŢIUNILOR CDTE-GATE
(CEP USM, 2014) Spalatu, Nicolae; Evtodiev, Igor; Caraman, Iuliana; Leontie, Liviu; Rotaru, Irina; Until, Dumitru; Caraman, Mihail
NANOLAMELLAR STRUCTURES OF OXIDE-AIIIBVI:Cd SEMICONDUCTORS TYPE FOR USE AS DETECTORS OF RADIATION IN THE UV SPECTRAL REGION
(Technical University of Moldova, 2011-07-07) Dmitroglo, Liliana; Untila, Dumitru; Chetruș, Petru; Evtodiev, Igor; Caraman, Iuliana; Lazăr, Gabriel; Nedeff, Valentin
In the paper, optical and photoelectrical properties of GaSe and InSe single crystal films of 10-5÷10-7 m submicron thickness and of semiconductor-native oxide structures obtained by annealing at (450÷700)°C in a normal atmosphere, are studied. The absorption spectrum of InSe lamella as well as of GaSe lamella in the energetic range from the red threshold up to 4,5 eV contains three bands with a rapid increase of the absorption coefficient which varies in the limits of (100÷106) cm-1 At the energies higher than 1,25 eV and 2,01 eV for InSe and GaSe respectively the light absorption are determined by the direct optical transitions in the centre of the Brillouin zone and at the energies higher than. At the absorption coefficients of (100÷102)cm-1 the indirect optic transitions are present. 3,0 eV also by the direct optical transitions in the points of the bands high symmetry. The resistive photosensitivity bands cover the spectral range Eg≤ hν ≤ 4,5 eV for lamellar photoresistors in which electric field EC6. The resistive photosensitivity band width could be controlled by the lamella thickness for d ≥1μm. The open circuit voltage spectral distribution is analysed from which results that at the oxidation temperature of 700°C in GaSe layer at the heterojunction interface the defects are formed on which the charge carriers, collected in the junction, are dissipated. The noneequilibrium charge carrier free path is of 0,8 μm.
OPTICAL AND PHOTOELECTRIC PROPERTIES OF NANOLAMELLAR STRUCTURES OBTAINED BY THERMAL ANNEALING OF InSe PLATES IN Zn VAPOURS
(John Wiley & Sons, 2018) Untila, Dumitru; Evtodiev, Igor; Caraman, Iuliana; Spalatu, Nicolae; Dmitroglo, Liliana; Caraman, Mihail
The structural, optical and photoelectric properties of InSe crystals grown by Bridgman–Stockbarger method and ZnSe/InSe structures obtained on InSe by thermal annealing in Zn vapours are studied in this paper. The study of structural properties confirms that ZnSe compound is formed. The analysis of photoelectric properties reveal that both the ZnSe‐InSe composite layer and the composite/InSe heterojunction are photosensitive in the VIS‐NIR spectral region. [ABSTRACT FROM AUTHOR]
OPTICAL AND PHOTOELECTRIC PROPERTIES OF NANOLAMELLAR STRUCTURES OBTAINED BY THERMAL ANNEALING OF INSE PLATES IN Zn VAPOURS
(2018) Untila, Dumitru; Evtodiev, Igor; Caraman, Iuliana; Spalatu, Nicolae; Dmitroglo, Liliana; Caraman, Mihail
The structural, optical and photoelectric properties of InSe crystals grown by Bridgman–Stockbarger method and ZnSe/InSe structures obtained on InSe by thermal annealing in Zn vapours are studied in this paper. The study of structural properties confirms that ZnSe compound is formed. The analysis of photoelectric properties reveal that both the ZnSe‐InSe composite layer and the composite/InSe heterojunction are photosensitive in the VIS‐NIR spectral region.
OPTICAL AND PHOTOSENSITIVE PROPERTIES OF FLEXIBLE n (p)–InSe/In2O3 HETEROJUNCTIONS
(2022) Sprincean, Veaceslav; Leontie, Liviu; Caraman, Iuliana; Untila, Dumitru; Girtan, Mihaela; Gurlui, Silviu; Lisnic, Petru; Doroftei, Corneliu; Cârlescu, Aurelian; Iaconi, Felicia; Caraman, Mihail
In this work, optical, including photoluminescence and photosensitivity, characteristics of micrometer-sized flexible n (p)–InSe/In2O3 heterojunctions, obtained by heat treatment of single- crystalline InSe plates doped with (0.5 at.%) Cd (Sn), in a water-vapor- and oxygen-enriched at- mosphere, are investigated. The Raman spectrum of In2O3 layers on an InSe:Sn substrate, in the wavelength range of 105–700 cm−1, contains the vibration band characteristic of the cubic (bcc-In2O3) phase. As revealed by EDX spectra, the In2O3 layer, ~2 μm thick, formed on InSe:Cd contains an ~18% excess of atomic oxygen. The absorption edge of InSe:Sn (Cd)/In2O3 structures was stud- ied by ultraviolet reflectance spectroscopy and found to be 3.57 eV and ~3.67 eV for InSe:Cd and InSe:Sn substrates, respectively. By photoluminescence analysis, the influence of doping impuri- ties on the emission bands of In2O3:Sn (Cd) was revealed and the energies of dopant-induced and oxygen-induced levels created by diffusion into the InSe layer from the InSe/In2O3 interface were determined. The n (p)–InSe/In2O3 structures display a significantly wide spectral range of photosen- sitivity (1.2–4.0 eV), from ultraviolet to near infrared. The influence of Cd and Sn concentrations on the photosensitivity and recombination of nonequilibrium charge carriers in n (p)–InSe layers from the heterojunction interface was also studied. The as-obtained nanosized InSe/In2O3 structures are suitable for optoelectronic applications.
OPTICAL PROPERTIES OF GaTe-ZnTe NANOLAMELLAE COMPOSITE
(2015) Spalatu, Nicolae; Evtodiev, Igor; Caraman, Iuliana; Evtodiev, Silvia; Rotaru, Irina; Caraman, Mihail; Untilă, Dumitru
A material composed of GaTe and ZnTe crystallites with average diameter of ~ 37 nm and 68 nm respectively was obtained by heat treatment at the temperature of 1000K and 1073K of GaTe plates in Zn vapour for 24 hours. The absorbance spectra of composite material obtained at 1073K and that calculated from diffuse reflection using the Kubelka-Munk formula contains the bands characteristic for light absorption in ZnTe and GaTe crystallites. The photoluminescence spectrum of composite material at the temperature of 80K is composed to the excitonic band in GaTe and impurity bands of ZnTe crystallites.
PHOTOELECTRIC AND PHOTOLUMINESCENCE PROPERTIES OF CdTe–GaTe COMPOSITE
(2016) Caraman, Iuliana; Spalatu, Nicolae; Evtodiev, Igor; Untila, Dumitru; Leontie, Liviu; Caraman, Mihail
A GaTe–CdTe composite was obtained by thermal treatment at 1020 K of GaTe single crystals in Cd vapor atmosphere. The composite photoluminescence, photoconductivity, and com- position are studied in this work. The photosensitivity and photoluminescence band structure are determined for both the primary crystals and the composite. The CdTe crystallites create, in the GaTe bandgap, recombination and trapping levels, which determine the structure of the photoluminescence spectra and the spectral range of composite photosensitivity. The photoluminescence spectrum of the composite at 80 K contains characteristic bands of both composite components, GaTe and CdTe. From the analysis of thermally stimulated luminescence curves, the energies of the electron trapping levels in the composite are determined.
PHOTOLUMINESCENCE OF NANOCOMPOSITES OBTAINED BY HEAT TREATMENT OF GaS, GaSe, GaTe AND InSe SINGLE CRYSTALS IN Cd AND Zn VAPOR
(2016) Evtodiev, Igor; Caraman, Iuliana; Kantser, Valeriu; Untila, Dumitru; Rotaru, Irina; Dmitroglo, Liliana; Evtodiev, Silvia; Caraman, Mihail
The photoluminescence (PL) spectra of GaS, GaSe, GaTe and InSe semiconductors used as the basis materials to obtain nanocomposite by heat treatment in Zn and Cd vapor were studied. The PL spectra of ZnS–GaS, CdSe– GaSe, CdSe–InSe, ZnSe–InSe composites consist of wide bands covering a wide range of wavelengths in the antistokes region for CdSe, ZnSe and GaS crystallites from composites. The antistokes branches of spectra are interpreted as the shift of PL bands to high energies for nanosized crystallites.
PHOTOLUMINESCENCE STUDIES OF THE INTERFACE OF CdS/CdTe HETEROJUNCTIONS
(2009) Vatavu, Sergiu; Zhao, Hehong; Caraman, Iuliana; Gașin, Petru; Morel, Don; Ferekides, Chris
The photoluminescence analysis of CdS/CdTe interface layer of CdS/CdTe heterojunction has been carried out in the 15- 100 K temperature range. An attempt to correlate observed PL features with the CdSxTe1–x layer presence at the interface of the heterojunctions was made. It is assumed the 1.525 eV band has an excitonic origin and 1.37X PL band is a characteristic impurity band due to CdSTe layer. Comparative plots showing SnO2/CdTe PL spectra are given as well.
PHOTOLUMINESENCE STUDIES OF CDTE/SNO2 AND CDTE/CDS HETEROJUNCTIONS: THE INFLUENCE OF OXYGEN AND THE CDCL2 HEAT TREATMENT
(Elsevier, 2011) Vatavu, Sergiu; Zhao, Hehong; Caraman, Iuliana; Gasin, Petru; Ferekides, Chris
The influence of oxygen and annealing in the presence of CdCl2 on the photoluminescence (PL) spectra of CdTe, component of SnO2/CdTe heterojunction (HJ), has been studied in a temperature range of 17–100 K. The changes in the photoluminescence spectra were studied as a function of excitation intensity. Analysis of the PL spectra was carried out with considerations of spectra obtained from CdS/CdTe heterojunctions. CdTe side PL (SnO2/CdTe HJ) consisted of 1.450 eV-DA defect band and 1.243 eV band (17 K). Annealing resulted in the disappearance of 1.243 eV band in oxygen containing samples. Interface PL for the unannealed samples consisted of mainly the 1.264 eV and a trace of the defect band. The CdCl2 treatment is responsible for an almost symmetrical 1.416 eV band.
PREPARATION, CHEMICAL COMPOSITION, AND OPTICAL PROPERTIES OF (β–Ga2O3 COMPOSITE THIN FILMS)/(GaSxSe1−x LAMELLAR SOLID SOLUTIONS) NANOSTRUCTURES
(2023) Sprincean, Veaceslav; Leontie, Liviu; Caraman, Iuliana; Lupan, Oleg; Adeling, Rainer; Gurlui, Silviu; Cârlescu, Aurelian; Doroftei, Corneliu; Caraman, Mihail
GaSxSe1−x solid solutions are layered semiconductors with a band gap between 2.0 and 2.6 eV. Their single crystals are formed by planar packings of S/Se-Ga-Ga-S/Se type, with weak polarization bonds between them, which allows obtaining, by splitting, plan-parallel lamellae with atomically smooth surfaces. By heat treatment in a normal or water vapor-enriched atmosphere, their plates are covered with a layer consisting of β–Ga2O3 nanowires/nanoribbons. In this work, the elemental and chemical composition, surface morphology, as well as optical, photoluminescent, and photoelectric properties of β–Ga2O3 layer formed on GaSxSe1−x (0 ≤ x ≤ 1) solid solutions (as substrate) are studied. The correlation is made between the composition (x) of the primary material, technological preparation conditions of the oxide-semiconducting layer, and the optical, photoelectric, and photoluminescent properties of β–Ga2O3 (nanosized layers)/GaSxSe1−x structures. From the analysis of the fundamental absorption edge, photoluminescence, and photoconductivity, the character of the optical transitions and the optical band gap in the range of 4.5–4.8 eV were determined, as well as the mechanisms behind blue-green photoluminescence and photoconduc- tivity in the fundamental absorption band region. The photoluminescence bands in the blue-green region are characteristic of β–Ga2O3 nanowires/nanolamellae structures. The photoconductivity of β–Ga2O3 structures on GaSxSe1−x solid solution substrate is determined by their strong fundamental absorption. As synthesized structures hold promise for potential applications in UV receivers, UV-C sources, gas sensors, as well as photocatalytic decomposition of water and organic pollutants.