Browsing by Author "Nedeoglo, Dmitrii"

Now showing 1 - 20 of 22

A comparative analysis of infrared luminescence spectra of ZnSe:Yb, ZnSe:Gd, and ZnSe:Cr crystals [Articol]
(Wiley, 2014) Colibaba, Gleb; Goncearenco, Evghenii; Nedeoglo, Dmitrii; Nedeoglo, Natalia
Photoluminescent and optical properties of ZnSe crystals doped with Yb and Gd rare-earth elements (REEs) and Cr impurity are investigated in infrared (IR) spectral range. The influence of stoichiometric deviation on photoluminescence (PL) spectra of the crystals is investigated and the structure of complex IR PL bands is analysed. The good coincidence between the IR PL spectra of the samples doped with Yb, Gd, and Cr is shown. Correlation between the component parts of the bands at 1 and 2 µm is found and possibility to control the composition of IR PL spectra by enrichment of the samples with Zn or Se is discussed. The model that explains the formation of associative centres based on the REEs and background Cu impurity fixed in the nodes of crystal lattice with tetrahedral symmetry, which are responsible for IR PL bands, is proposed. (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
Effect of annealing of ZnSe:Cr crystals in Bi(Zn) melt on the intensity of radiation bands of Cr ions [Articol]
(2010) Kulyuk, Leonid; Nedeoglo, Dmitrii; Siminel, Anatolii; Sushkevich, Constantin
The photoluminescence in visible and near-IR spectral range of ZnSe:Cr as-grown and annealed in Bi(Zn) melt crystals was investigaded at room temperature. It was established that heat treatment of the crystals in Bi melt does not lead to chrome extraction, but their annealing in Zn melt results in partial extraction into melt of chrome and some other shallow impurities.
Enhanced Responsivity of ZnSe-bazed Metal-Semiconductor-Metal Near-Ultraviolet Photodetector via Impact Ionization [Articol]
(Willey, 2018) Sirkeli, Vadim; Yilmazoglu, Oktay; Hajo, Ahid S.; Nedeoglo, Natalia; Nedeoglo, Dmitrii; Preu, Sascha; Küppers, Franko; Hartnagel, Hans
We report on high‐responsivity, fast near‐ultraviolet photodetectors based on bulk ZnSe employing a metal–semiconductor–metal structure with and without interdigital contacts. A very high responsivity of 2.42 and 4.44 A W−1 at 20 V bias voltage and high rejection rate of 7900 and 4810 for the light with a wavelength of 325 nm is obtained for photodetectors without and with interdigital contacts, which indicates an internal gain. The mechanism of internal gain is attributed to the impact ionization of ZnSe atoms under high internal electric field strength of 133 kV cm−1. Also a low dark current of ≈3.4 nA and high detectivity of ≈1.4 × 1011 cm Hz1/2 W−1 at a voltage of 20 V is achieved for the device with interdigital contacts at room temperature.
Growth technology for ZnSe single crystals with low dislocation density [Articol]
(2008) Colibaba, Gleb; Nedeoglo, Dmitrii
The influence of the growth temperature, undercooling, growth rate as well as growth chamber construction and furnace temperature profile on the structural perfection of the crystals grown by both physical and chemical vapors transport has been investigated. The conditions for growing of crystals free from subgrain boundaries and twins are suggested. The etch pits are not observed in the basic volume (up to 4 сm3) of grown crystals. It is shown, that PL spectra of as-grown ZnSe crystals consist of the edge radiation only. The resistivity of ZnSe crystals annealed in a Zn melt is higher than 108 Ohmcm, whereas the electrical conductivity of ZnSe:I crystals grown by chemical vapor transport and annealed in a Zn melt is 10 (Ohm⋅cm)-1 at room temperature.
High performance ZnSe-based ultraviolet photodetectors with Cr/Au, Ni/Au and hybrid Ag-nanowire contacts [Articol]
(2024) Sirkeli, Vadim; Nedeoglo, Natalia; Nedeoglo, Dmitrii; Yilmazoglu, Oktay; Hajo, Ahid; Preu, Sascha; Küppers, Franko; Hartnagel, Hans
Impurity distribution in n-ZnSe crystals doped with Au [Articol]
(2005) Nedeoglo, Dmitrii; Nedeoglo, Natalia; Sirkeli, Vadim
Hall effect, electric conductivity and mobility of charge carriers in n-ZnSe single crystals doped with Au are investigated in the temperature range from 77 to 300 K. Impurity distribution in the crystals was studied by a method of “layer-by-layer” etching of a sample surface. The model, which explains this distribution by a simultaneous diffusion of Zn and Au atoms during a long-term high-temperature annealing of as-grown crystals in Zn + Au melt, is proposed.
Infrared photoluminescence of ZnSe:Gd crystals [Articol]
(Elsevier, 2015) Colibaba, Gleb; Goncearenco, Evghenii; Nedeoglo, Dmitrii; Nedeoglo, Natalia
Photoluminescent and optical properties of ZnSe crystals doped with Gd impurity are investigated in infrared (IR) spectral range. The influence of crystal growth temperature, impurity concentration, stoichiometric deviation and post-annealing cooling rate, concentration of Cr and Cu background impurities, temperature and excitation level on photoluminescent and optical properties of the samples is studied. Based on these investigations, the structure of complex IR photoluminescence (PL) bands is analyzed. Correlation between the component parts of the bands at 1 and 2 µm is found and possibility to control the IR PL spectra by enrichment of the samples with Zn or Se is discussed. Coincidence of the IR PL spectra structure is shown for the samples doped with Gd, Yb, and Cr impurities. The model that explains the formation of complexes based on rare-earth elements (REEs) and Cr and Cu background impurities fixed in the nodes of crystal lattice with tetrahedral symmetry, responsible for IR PL bands, is proposed.
Interaction of intrinsic defects with impurities in Al doped ZnSe single crystals [Articol]
(American Institute of Physics, 2007) Ivanova, G.N.; Nedeoglo, Dmitrii; Nedeoglo, Natalia; Sirkeli, Vadim
We report on the results of a complex study of electrical (77−300 K) and luminescence (10−300 K) properties of 𝑛-ZnSe single crystals annealed in a Zn melt containing Al impurity at concentrations ranging from 0.1 to 80 at. %. It was established that Al atoms form donor centers only at a low impurity concentration (≤0.5 at. %). The increase of the amount of Al atoms in the crystal results in the formation of (VZnAlZn) associative acceptor centers leading to the self-compensation of the shallow Al donor impurity. This process is accompanied by the emergence and development of a self-activated luminescence band associated with the (VZnAlZn) acceptor centers. We show that further increase of the Al content in the melt (≥10 at. %) leads to the dissociation of the acceptor complexes and to a recurrent donor doping effect. The photoluminescence spectra of such crystals are dominated by activated luminescence via the (CuZnVSeCu𝑖) and (CuZnAlZn) associative centers.
Luminescent properties of Sb-doped ZnSe single crystals [Articol]
(2019) Sushkevich, Konstantin; Goncearenco, Evghenii; Nedeoglo, Natalia; Nedeoglo, Dmitrii
Photoluminescence (PL) spectra of ZnSe:0.1at%Sb single crystals are studied between 90 and 300 K. The samples are grown by the chemical vapor transport (CVT) method with iodine as a transport agent and doped with Sb impurity during the growth. A yellow PL band with a maximum at 2.16 eV (575 nm) at room temperature is observed for the first time. A model of a (SbSeISe) acceptor center with the energy level located at 0.52 eV above the valence band edge is proposed, and the mechanism of the formation of this yellow PL band under direct and indirect excitation is discussed.
Luminescent properties of ZnO powders synthesized by isovalent method [Articol]
(2016) Goglidze, Tatiana; Dementiev, Igor; Koval, Andrei; Nedeoglo, Natalia; Nedeoglo, Dmitrii
Zinc oxide powders have been prepared by the isovalent substitution method by means of high - temperature annealing of a zinc sulfide powder synthesized by a chemical method. Investigation of photoluminescence (PL) spectra in dependence on annealing temperat ure varied from 870 to 1050  С has made it possible to find the temperature range of 920 – 950  С for the most active isovalent substitution of oxygen atoms for sulfur atoms and the formation of a ZnO  S phase. X - ray diffraction analysis has revealed that the p owder with crystal lattice parameters а о = 0.3249 nm and с о = 0.5206 nm and the ratio of с о / а о = 1.60, which are characteristic of zinc oxide crystals, is synthesized at the maximum annealing temperature. It has been found that the maximum of a structurel ess PL band in the spectrum for the ZnO powder at room temperature is localized at 500 nm. It has been supposed that the band is caused by ―free electron – acceptor‖ radiative transitions, where the acceptor level is 0.95 eV above the valence band edge.
Magnetic and luminescent properties of iron-doped ZnSe crystals [Articol]
(Elsevier, 2010) Kulyuk, Leonid; Nedeoglo, Dmitrii; Nedeoglo, Natalia; Radevici, Ivan; Sirkeli, Vadim; Sushkevich, Konstantin
Magnetic and luminescent properties of ZnSe crystals doped with Fe by various methods are studied. It is established that Fe impurity is responsible for photoluminescence (PL) bands at 980, 1320, 1450 nm and quenches PL band at 630–645 nm. It is found that magnetic properties of ZnSe:Fe crystals are sensitive to the doping method. At low fields, two magnetic subsystems may be observed for the samples doped with Fe during the growth process—weak paramagnetic subsystem and antiferromagnetic subsystem with TС=–130 K. For the samples doped with Fe by high-temperature annealing in Zn melt, few magnetic subsystems may be distinguished, however, the magnetic properties are typical for spin glasses with the transition temperature Tsg=(45–50) K.
Magnetic and luminescent properties of nickel-doped ZnSe crystals [Articol]
(Elsevier, 2015) Sirkeli, Vadim; Radevici, Ivan; Sushkevich, Konstantin; Nedeoglo, Natalia; Nedeoglo, Dmitrii
Magnetic and photoluminescent properties of nickel-doped ZnSe crystals with impurity concentrations varied by changing the Ni amount in the source material from 0.001 to 0.50 at.% are studied in 5–300 K temperature range. Investigation of magnetic properties shows that Ni impurity in ZnSe forms isolated paramagnetic centers and probability of Ni–Ni pairs formation is negligible due to low Ni concentration in the samples. The contribution of Ni impurity to edge emission and its influence on infra-red emission are discussed. It is found that complete concentration quenching of luminescence within all studied spectral range is observed starting with Ni concentration of 0.50 at.%.
Obtaining of II-VI compound substrates with controlled electrical parameters and prospects of their application for nanoporous structures [Articol]
(John Wiley & Sons, 2014) Colibaba, Gleb; Goncearenco, Evghenii; Nedeoglo, Dmitrii; Nedeoglo, Natalia; Monaico, Eduard; Tiginyanu, Ion
Photoluminescence of n-ZnSe single crystals doped with iodine by vapour phase diffusion [Articol]
(2006) Avdonin, A.N.; Nedeoglo, Dmitrii; Nedeoglo, Natalia; Sirkeli, Vadim; Ivanova, G.N.
Photoluminescence spectra of n-ZnSe single crystals doped with iodine are investigated in the temperature range from 83 to 300 K. It is shown that the edge PL band is formed by overlapping of the PL lines attributed to ISe donor-bound ecxitons (I2I) and VZn acceptorbound excitons (D1I). A model of radiation mechanisms, which explain the redistribution of the edge and long-wave PL bands intensities with increasing doping level of the samples, is proposed.
Photoluminescence of ZnSe samples doped with antimony and iodine [Articol]
(Elsevier, 2021) Sushkevich, Konstantin; Goncearenco, Evghenii; Nedeoglo, Natalia; Nedeoglo, Dmitrii
Photoluminescence (PL) spectra of ZnSe samples grown by Chemical Vapour Transport (CVT), Physical Vapour Transport (PVT), and from melt have been studied in the temperature range from 100 to 300 K. Impurity-defect composition of the studied samples was varied by doping with antimony (Sb) or iodine (I), as well as co-doping with Sb and I, both during the crystal growth and crystal annealing in the respective melts. It is established that the PL band with maximum at (570–580) nm is present only in the spectra for ZnSe samples co-doped with Sb and I, independent of growth technique mand doping method. The (SbSe–ISe) radiative centre, with the energy level placed 0.5 eV above the valence band top, is proposed to be responsible for this PL band.
Photoluminescence study of ZnO nanostructures grown on silicon by MOCVD [Articol]
(Elsevier, 2012) Sirkeli, Vadim; Nedeoglo, Dmitrii
ZnO nanostructures with a size ranging from 20 to 100 nm were successfully deposited on (1 0 0)-Si substrates at different temperatures (500–800 °C) using MOCVD. It could be confirmed that the size of ZnO nanostructures decreased with increasing growth temperature. From photoluminescence (PL) studies it was found, that intensive band-edge PL of ZnO nanostructures consists of emission lines with maxima at 368.6 nm, 370.1 nm, 373.7 nm, 383.9 nm, 391.7 nm, 400.7 nm and 412 nm. These lines can be dedicated to free excitons and impurity donor-bound excitons, where hydrogen acts as donor impurity with an activation energy of about 65 meV. A UV shift of the band-edge PL line with increasing growth temperature of ZnO nanostructures was observed as a result of the quantum confinement effect. The results suggest that an increase of growth temperature leads to increased band-edge PL intensity. Moreover, the ratio of band-edge PL intensity to green- (red-) band intensity also increases, indicating better crystalline quality of ZnO nanostructures with increasing growth temperature.
Purification of ZnSe crystals from electrically active background impurities by ytterbium doping [Articol]
(John Wiley & Sons, 2014) Radevici, Ivan; Sushkevich, Konstantin; Sirkeli, Vadim; Nedeoglo, Dmitrii; Nedeoglo, Natalia; Huhtinen, Hannu; Paturi, Petriina
Hall coefficient, electrical conductivity, and electron mobility are investigated for n-ZnSe:Yb single crystals with high concentration of electrically active background impurities
Self-absorption of violet radiation in ZnO thin films produced on ZnSe crystal surfaces by isovalent substitution method [Articol]
(Elsevier, 2018) Goglidze, T.I.; Dementiev, I.V.; Covali, A.V.; Goncearenco, E.P.; Nedeoglo, Natalia; Nedeoglo, Dmitrii
Photoluminescence (PL) spectra of ZnO thin films produced by isovalent substitution method by means of thermal treatment of zinc selenide single crystal substrates in air are studied in 350 – 750 nm range at room temperature. Irrespective of annealing temperature (500 – 870 °C) and annealing time (20 – 120 min), PL spectra consist of a short-wavelength violet radiation with maximum localized between 396 and 423 nm and a long-wavelength yellow-orange radiation with maximum localized between 575 and 600 nm. Both PL bands are attributed to donor-acceptor (DA) pairs. It is shown that the violet PL band intensity decreases and the yellow-orange PL band intensity increases with increasing ZnO film thickness that is caused by self-absorption of the short-wavelength radiation and energy transmission to DA-pair centres of the long-wavelength radiation.
Shallow donor states induced in ZnNe :au single crystals by lattice deformation [Articol]
(American Institute of Physics, 2008) Nedeoglo, Natalia; Nedeoglo, Dmitrii; Laiho, R.; Sirkeli, Vadim; Lähderanta, E.
Photoluminescence (PL) spectra are investigated in n-ZnSe single crystals at different temperatures from 4.4 to 300 K immediately after doping with Au from melt of Se+Au or Zn+Au and after storage of the doped samples for 4 years in the dark under normal room conditions. Due to the formation of Aui interstitial donors in the n-ZnSe:Se:Au crystals with time, the origin of the near band edge PL changes from acceptor-bound to donor-bound excitons. Taking into account the results of PL characterization, we proposed that the Aui donors are generated by displacement of Au ions from regular lattice sites to interstitial sites with the help of lattice deformation forces. Transport measurements show dramatic increase in the electrical conductivity and the free electron concentration after storage of the n-ZnSe:Zn:Au crystals, thus confirming the proposed model.
Simulation et modelisation de la variation de la mobilite de hall des photoelectrons en fonction de la temperature dans les cristaux de n-ZnSe :Zn irradies avec des electrons energetiques [Articol]
(Université Mentouri, 2007) Djouadi, D.; Boughiden, B.; Chelouche, A.; Nedeoglo, Dmitrii
Dans l’intervalle de températures [77..300 K] a été mesurée la mobilité de Hall des électrons d’équilibre et des photoélectrons dans les cristaux de n-ZnSe :Zn irradiés avec un faisceau d’électrons d’énergie E=1,3 MeV et dont la dose d’irradiation varie entre 2,73 1016 et 5.19 1017 électrons/cm2 . Le comportement de la mobilité des photoélectrons s’explique parfaitement dans le cadre d’un modèle à deux-barrières d’un semiconducteur inhomogène représentant une matrice faiblement ohmique contenant des inclusions fortement ohmiques (clusters). En se basant sur les théories de Shik et de Petrossiyan , une expression approximative de la mobilité de Hall a été obtenue. Il a été montré que ce modèle fonctionne parfaitement pour les petites doses d’irradiation. Lorsque la dose dépasse une certaine valeur critique ( D= 2.98 1017 électrons /cm2) le modèle considéré passe au modèle du potentiel à relief aléatoire.