Facultatea de Fizică şi Inginerie / Faculty of Physics and Engineering

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Author: search.filters.author.Leontie, LiviuSubject: search.filters.subject.Thin films

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    Study of generation-recombination processes of non-equilibrium charge carriers in single crystalline thin GaSe(Cu) films [Articol]
    (2006) Cuculescu, Elmira; Evtodiev, Igor; Caraman, Mihail; Leontie, Liviu
    The generation-recombination processes of non-equilibrium charge carriers in undoped and Cu-doped (in the range 0.1-0.5 at.%.) single crystalline GaSe films with thickness d in the range 1.5-225 μm are investigated. Cu doping of GaSe crystals up to 0.5 at.% leads to an increase of electrical conductivity by over 4 orders of magnitude, as well to enhancement of impurity luminescence band (PL) and extension of photoconductivity spectral range. By studying PL and photonductivity spectra, for different excitation (photon) energies in temperature range (78-420) K, energies of localized states due to both Cu and accidental impurities are determined. By analysing temperature dependence of electrical conductivity and photoconductivity for undoped and Cu-doped films, the activation energy of acceptor levels in doped films was determined as 0.058 and 0.025 eV. Increasing Cu doping from 0.1 to 0.5 at.%. results in decreasing energy of acceptor levels up to ∼0.02 eV. By analysing the impurity absorption and photoconduction at 78 K the energy of acceptor levels was determined as 12-15 meV greater than previously evaluated, depending on Cu concentration. For films with d<5 μm, the surface states concentration increased for Cu doping over 0.3 at.%.
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    On the photoconductivity of Bi2O3 in thin films [Articol]
    (2000) Leontie, Liviu; Caraman, Mihail; Rusu, Gheorghe Ioan
    The spectral characteristics of photoconductivity for Bi2 O3 thin films were investigated. The films were prepared by thermal oxidation in air of Bi evaporated films. As revealed by X-ray diffraction and polarizing microscopy studies, polycrystalline and multiphasic films were obtained. From the photoconductivity spectral curves, the bandgap energy values were determined, by using the Moss criterion. The influence of oxidation (preparation) conditions on the Eg values is discussed. The photoconductivity of Al-Bi 2 O3 -Al, Cu-Bi 2 O3 -Cu and Al- Bi 2 O3-In 2 O3 structures is also investigated.