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    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.
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    THE ANALYSIS OF CURRENT FLOW MECHANISM IN CDS/CDTE HETEROJUNCTION
    (Elsevier, 2007) Vatavu, Sergiu; Gașin, Petru
    An analysis of current–voltage dependencies of CdS/CdTe heterojunction in the 78–370 K temperature range has been carried out. According to this analysis the current flow mechanism is determined by the tunneling processes through dislocations, which penetrate the heterojunction space charge region. The concentration of dislocations has been estimated as 2 · 105 cm− 2. The number of steps necessary for tunneling varies: 2.5 · 102–1.7 · 103. The characteristic energy has a weak temperature dependence (− 0.2 meV/K) and its value vary 120–200 meV. The increase of the annealing duration results in the decrease of the characteristic energy. The multistep tunneling processes through local centres, determined by impurity centres, interface states and defects in the space charge region, predominate at reverse biases. The number of tunneling steps is 1–4 · 102. The concentration of local centres (traps) in the heterojunction have been estimated as 2.37 · 105–1.63 · 106 cm− 3. The thermal annealing in the presence of CdCl2 up to 60 min does not modify the current flow mechanism in CdS/CdTe heterojunctions.
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    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.
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    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.
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    THE EFFECT OF Cu AND ANNEALING TREATMENTS ON CdS/CdTe HETEROSTRUCTURES STUDIED WITH QE AND PHOTOCURRENT RELAXATION TECHNIQUES
    (IEEE, 2008) Zhao, H.; Vatavu, Sergiu; Caraman, Iu. M.; Gasin, P. A.; Morel, D. L.; Ferekides, C. S.
    The photo-emf (photocurrent) decay al light impulses excitation (in longitudinal configuration) has been used to determine the lifetime of the non-equilibrium charge carriers recombining in different regions of the CdS/CdTe Cu containing heterojunction at different temperatures and biases. The photosensitivity spectral distributions have been investigated for samples with different technological variations.
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    THE INVESTIGATION OF TCO/CdS/CdTe HETEROJUNCTIONS BY C-U and C-f MEASUREMENTS: EXPERIMENT AND MODELING
    (IEEE, 2013) Rotaru, Corneliu; Vatavu, Sergiu; Fedorov, Vladimir; Gașin, Petru; Lux-Steiner, Martha; Ferekides, Chris; Rusu, Marin
    The paper presents the analysis of C-U and C-f data obtained in the 1 kHz-10 MHz range for CdS/CdTe heterojunctions prepared by CSS onto (ZnO:Al, ZnO:Al/i-ZnO)/Glass substrates. An attempt to model the physical properties of the heterojunctions is made. A small signal analysis has been carried out to establish the equivalent circuit of device. The unusual capacitance behavior of the ZnO based heterojunction is attributed to presence of the barrier at the back contact.