Mihail Caraman - Academia.edu (original) (raw)

Papers by Mihail Caraman

Research paper thumbnail of Optical and photosensitive properties of lamellar nanocomposites obtained by Cd intercalation of GaTe

By Cd-vapor heat treatment, at temperatures from 623 to 833 K, of GaTe single crystals, GaTe-CdTe... more By Cd-vapor heat treatment, at temperatures from 623 to 833 K, of GaTe single crystals, GaTe-CdTe composite is formed. CdTe amount is increasing together with heat treatment temperature. Absorption, photoconductivity and photoluminescence spectra of the composite contain particularities characteristic to GaTe and CdTe components. The absorption and photoconductivity edges display two thresholds at 1.66 eV (GaTe) and 1.50 eV (CdTe). Short lifetime recombination states form at the surface of composite samples, leading to narrowing of the photoconductivity bands in the high energy region, up to 1.8 eV.

Research paper thumbnail of SOME OPTICAL PROPERTIES OF GaSe CRYSTALS DOPED WITH ELEMENTS OF GROUP I (Li AND K)

Research paper thumbnail of THE PHOTOCONDUCTIVITY OF GaSe< < < > > > CRYSTALS

The presents a study of the photoconductivity spectra of the GaSe crystals within UV, visible and... more The presents a study of the photoconductivity spectra of the GaSe crystals within UV, visible and near IR spectral domains at the temperatures 78K to 293K. The mechanisms of generation and recombination of the charge nonequilibrium carried by the surface states were established.

Research paper thumbnail of Absorption spectra and extrinsic photoconductivity of Cu and Cd doped GaSe single - crystal films

GaSe single crystal films were doped during growth process with Cu or Cd atoms with concentration... more GaSe single crystal films were doped during growth process with Cu or Cd atoms with concentration ranged between 0.05 and 0.50 at. %. Single crystal films (with thickness about 0.5 μm) were obtained by mechanical splitting of bulk single crystals. Impurity concentration was determined using atomic emission spectroscopy. Spectral dependences of absorption coefficient and photoconductivity were studied in the range 1.50 eV - 3.70 eV. It was experimentally established that the absorption spectra have an additional absorption band and its corresponding energy depends on the nature (Cu or Cd) and concentration of the doping atoms. Also, independently on the presence of the dopant, other two absorption bands in the IR region are present.

Research paper thumbnail of OPTICAL AND PHOTOELECTRICAL CHARACTERISTICS OF GaSe (Cu)/OXIDE SEMICONDUCTOR HETEROJUNCTION

Research paper thumbnail of Study of generation-recombination processes of non-equilibrium charge carriers in single crystalline thin GaSe (Cu) films

Journal of Optoelectronics and Advanced Materials

The generation-recombination processes of non-equilibrium charge carriers in undoped and Cu-doped... more 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 a...

Research paper thumbnail of ELLIPSOMETRIC STUDIES OF NANOMETRIC CdS AND CdTe FILMS

Experimental Methods in the Physical Sciences

The thickness of the layers CdS and CdTe grown on the Si, Ge, GaAs was determined from the analys... more The thickness of the layers CdS and CdTe grown on the Si, Ge, GaAs was determined from the analysis of the polarization ellipse of the reflected light from the surfaces of structures thin layers substrate. The thermal treatment of the samples CdS-CdTe in the presence of CdCl 2 leads to the increasing of the crystalline phase from layers.

Research paper thumbnail of INVESTIGATION OF ENERGETIC STATES, DETERMINED BY Cu AND Cd IMPURITY ATOMS, AT SURFACE OF GaS AND GaSe MONOCRYSTALLINE LAYERS

The reflection, absorption, photoconductivity, and thermally stimulated luminescence (TSL) spectr... more The reflection, absorption, photoconductivity, and thermally stimulated luminescence (TSL) spectra of GaS:Cu and GaSe:Cu, Cd single crystals have been studied. As a result of these investigations, the energy diagram of GaS and GaSe crystals after doping was deter- mined.

Research paper thumbnail of <title>Surface structure of CdS layer at the interface of CdS-SnO<formula><inf><roman>2</roman></inf></formula> junction and the diagram of surface states</title>

Advanced Topics in Optoelectronics, Microelectronics, and Nanotechnologies IV, 2009

ABSTRACT The SnO2-CdS type structures with SnO2 film deposited by thermal pirolize in SnCl4-etano... more ABSTRACT The SnO2-CdS type structures with SnO2 film deposited by thermal pirolize in SnCl4-etanol solution were obtained. The CdS film with submicron thickness was obtained in cvasiclosed volume. The transversal section of the SnO2-CdS junction as well as the outer surface of the CdS film was analyzed using the electronic microscope. The density of the crystallization germs in the CdS film was about 1013cm-2. The luminescence spectrum of CdS has been examined. The existence of exciton line (n=1) in reflection and emission spectrum serves as a criteria of crystalline perfection of surface film.

Research paper thumbnail of Structural and optical characteristics of bismuth oxide thin films

Surface Science, 2002

The formation of different phases of Bi-O system during oxidizing process of Bi films from the vi... more The formation of different phases of Bi-O system during oxidizing process of Bi films from the viewpoint of structure characteristics and optical properties, is investigated. As revealed by structure and surface investigations, the thermal oxidation, in air, of Bi films on glass results in polycrystalline and multiphase bismuth oxide films. At substrate-film interface an amorphous oxide layer forms up, to whom surface the growth processes of crystallites belonging to divers phases, with different geometric shapes occur. For nanometric up to submicronic thicknesses, BiO is predominant phase, while in case of micronic films, a-Bi 2 O 3 and Bi 2 O 3 are the main phase components. From absorption curves the band gap values, (E g ¼ 2:29-3:31 eV), for direct transitions, have been determined and an energy gap of $2 eV for amorphous phase was found. Ó

Research paper thumbnail of <title>Optical bistability in GaSe single crystals and ZnTe thin films</title>

ROMOPTO '94: Fourth Conference in Optics, 1995

ABSTRACT By means of two-beam experiments, the transmission properties of highly excited GaSe cry... more ABSTRACT By means of two-beam experiments, the transmission properties of highly excited GaSe crystal of different thicknesses (2 micrometers to 1.5 mm) have been investigated in the fundamental absorption and free exciton region. Induced transmission was observed in the whole considered region for lower pump intensities. Results of bistability in an entire ZnTe thin films are present for the first time.

Research paper thumbnail of Low-temperature Photoluminescence Studies of CdTe Thin Films Deposited on CdS/ZnO/Glass Substrates

MRS Proceedings, 2013

The CdTe photoluminescence spectra of CdTe/CdS/ZnO heterojunctions annealed in the presence of Cd... more The CdTe photoluminescence spectra of CdTe/CdS/ZnO heterojunctions annealed in the presence of CdCl 2 have been analyzed in the 4.7-100K temperature range. The analysis has been performed for laser excitation power between 0.01 mW and 30 mW. The analysis showed that the photoluminescence spectrum in the 1.1-1.6 eV region consists of a defect band (1.437 eV) having complex structure and revealing well contoured LO phonon replicas and bound exciton annihilation in the 1.587-1.593 eV region. The band analysis has been carried out by deconvoluting the spectra. It has been shown that the defect band consists of two elementary bands and their phonon replica. An "unusual" temperature dependence of the defect band has been found.

Research paper thumbnail of A comparative study of (ZnO, In2O3: SnO2, SnO2)/CdS/CdTe/(Cu/)Ni heterojunctions

Thin Solid Films, 2013

ABSTRACT The influence of the manufacturing technology on the structural properties of CdTe and C... more ABSTRACT The influence of the manufacturing technology on the structural properties of CdTe and CdS layers, components of the CdS/CdTe solar cells, has been investigated. CdTe based solar cells have been prepared using glass substrates coated with different transparent conductive oxides (TCOs: SnO2, In2O3: SnO2 (ITO), ZnO:Al, ZnO:Al/i-ZnO).The analysis of the technology combined with various investigation methods allowed to determine optimum deposition parameters for CdS and CdTe for each type of TCO used. X-ray diffraction (XRD) and grazing incidence XRD analysis have been carried out for TCO, CdS, and CdTe layers at different deposition stages before and after annealing in the presence of CdCl2 in air. The reflection spectra in the 100–600 cm− 1 spectral region have been thoroughly studied by using Fourier transform infrared spectroscopy. It was found that (i) the best quality possess CdS and CdTe thin films sequentially deposited on ZnO:Al substrates and that (ii) the pre-treatment defects can be effectively cured and most of the secondary phases can be removed by annealing, while the basic structure of the investigated thin films does not essentially change.

Research paper thumbnail of Optical and photoelectrical properties of GaS and CdTe thin FILMS, components of GaS/CdTe heterojunctions

In the paper, experimental results concerning the absorption and photosensibility spectral depend... more In the paper, experimental results concerning the absorption and photosensibility spectral dependence of GaS and CdTe thin film components of GaS/CdTe heterojunctions are presented. GaS films (d = 0.06 µm -2.8 µm) were deposited onto ITO substrate by laser light pulses. CdTe films (d = 3.6 µm) were deposited onto GaS films by close-spaced sublimation technique. At the fundamental absorption edge, the absorption coefficient of CdTe layers increases of five orders of magnitude in a narrow 40 -100 meV energy range, up to 4 10 4 cm -1 . At room temperature, the energy band of GaS/CdTe heterojunctions photosensitivity is 1.45 eV-2.75 eV, the photocurrent having a constant value up to 2.0 eV photon energy.

Research paper thumbnail of Thin Solid Films 480-481

Research paper thumbnail of BISTABLE OPTIC MODULATORS MADE FROM MONOCRYSTALLINE LAYERS GaSe (Cu)

Fabry-Perot interferometer was constructed on the basis of parallel - slides plates cut off from ... more Fabry-Perot interferometer was constructed on the basis of parallel - slides plates cut off from the GaSe(Cu) single crystals with Cu concentration of 0.05 at%. The thickness of these plates was equal to 5 ÷ 10 μm. Dielectric glass, which consisted of 7 ZnS layers and 7 MgF2 layers with λ/4 thickness, was placed on lateral surfaces of the plates. The reflectance of the glass was equal to ~ 73%. The dependence of interferometer transparency on the intensity of incident radiation with 0.6328 μm wavelength is studied. The threshold intensity, for which periodic pulsations of transmission are observed, is determined from this dependence.

Research paper thumbnail of Non-equilibrium charge carriers generation — recombination mechanisms at the interface of the SnO2/GaSe heterojunction

Thin Solid Films, 2009

The interface of the SnO 2 /GaSe heterojunctions, having SnO 2 layer obtained by different deposi... more The interface of the SnO 2 /GaSe heterojunctions, having SnO 2 layer obtained by different deposition methods have been studied using the photoluminescence and photocurrent spectral distribution. The SnO 2 /GaSe structures are photosensitive in the 1.7 ÷ 3.6 eV spectral range and reveal its maximum value for the heterojunctions with magnetron sputtered SnO 2 layer.

Research paper thumbnail of On the optical properties of bismuth oxide thin films prepared by pulsed laser deposition

Thin Solid Films, 2005

The optical properties of bismuth oxide films prepared by pulsed laser deposition (PLD), absorpti... more The optical properties of bismuth oxide films prepared by pulsed laser deposition (PLD), absorption in the photon energy range 2.50-4.30 eV and optical functions (n, k, e 1 , and e 2 ) in the domain 3.20-6.50 eV, have been investigated. As-prepared films (d=0.05-1.50 Am) are characterized by a mixture of polycrystalline and amorphous phases. The fundamental absorption edge is described by direct optical band-toband transitions with energies 2.90 and 3.83 eV. The dispersion of the optical functions provided values of 4.40-6.25 eV for electron energies of respective direct transitions. In the spectral range 400-1000 nm, bismuth oxide films show a normal dispersion, which can be interpreted in the frame of a single oscillator model. D

Research paper thumbnail of The influence of thermal annealing in presence of CdCl2 on the electrophysical properties of the CdS/CdTe solar cells

Thin Solid Films, 2005

ABSTRACT The investigation of the charge carrier energy states in CdS/CdTe solar cells was based ... more ABSTRACT The investigation of the charge carrier energy states in CdS/CdTe solar cells was based on the studies of absorption and photoconductivity spectral dependencies, quantum efficiency, photoconductivity kinetics measurements at 78 and 300 K. The analysis of the absorption spectra of cadmium telluride (CdTe) films used as a component of SnO2/CdS/CdTe/Ni solar cells, had shown that its heat treatment in CdCl2 leads to the formation of an impurity level localized at ∼20 meV from the top of CdTe valence band. The high photovoltaic properties of the SnO2/CdS/CdTe/Ni solar cells are determined by the presence of the recombination level with a lifetime equal to 180 μs. The heterojunctions heat treatment in CdCl2 leads to the structure defects removal in the semiconductor layers, recrystallization of CdS film and to the formation of CdSxTe1−x (x∼0.95) solutions at the interface.

Research paper thumbnail of Photoelectrical properties of layered GaS single crystals and related structures

Materials Research Bulletin, 2008

The photoconductivity of pure and Cu-doped layered gallium monosulfide (GaS) single crystals, and... more The photoconductivity of pure and Cu-doped layered gallium monosulfide (GaS) single crystals, and of Ni-GaS(Cu)-In and GaS(Cu)-ZnO structures, is investigated. The activation energies of surface states were found as 0.10 eV, 0.40 eV and 17 meV, $400 meV for GaS and GaS(Cu), respectively. Cu acceptor levels are localized at 0.44 eV and 0.52 eV above the valence band of GaS. ZnO-GaS(Cu) heterojunctions show remarkable photosensitivity in the wavelength range of 250-700 nm. #

Research paper thumbnail of Optical and photosensitive properties of lamellar nanocomposites obtained by Cd intercalation of GaTe

By Cd-vapor heat treatment, at temperatures from 623 to 833 K, of GaTe single crystals, GaTe-CdTe... more By Cd-vapor heat treatment, at temperatures from 623 to 833 K, of GaTe single crystals, GaTe-CdTe composite is formed. CdTe amount is increasing together with heat treatment temperature. Absorption, photoconductivity and photoluminescence spectra of the composite contain particularities characteristic to GaTe and CdTe components. The absorption and photoconductivity edges display two thresholds at 1.66 eV (GaTe) and 1.50 eV (CdTe). Short lifetime recombination states form at the surface of composite samples, leading to narrowing of the photoconductivity bands in the high energy region, up to 1.8 eV.

Research paper thumbnail of SOME OPTICAL PROPERTIES OF GaSe CRYSTALS DOPED WITH ELEMENTS OF GROUP I (Li AND K)

Research paper thumbnail of THE PHOTOCONDUCTIVITY OF GaSe< < < > > > CRYSTALS

The presents a study of the photoconductivity spectra of the GaSe crystals within UV, visible and... more The presents a study of the photoconductivity spectra of the GaSe crystals within UV, visible and near IR spectral domains at the temperatures 78K to 293K. The mechanisms of generation and recombination of the charge nonequilibrium carried by the surface states were established.

Research paper thumbnail of Absorption spectra and extrinsic photoconductivity of Cu and Cd doped GaSe single - crystal films

GaSe single crystal films were doped during growth process with Cu or Cd atoms with concentration... more GaSe single crystal films were doped during growth process with Cu or Cd atoms with concentration ranged between 0.05 and 0.50 at. %. Single crystal films (with thickness about 0.5 μm) were obtained by mechanical splitting of bulk single crystals. Impurity concentration was determined using atomic emission spectroscopy. Spectral dependences of absorption coefficient and photoconductivity were studied in the range 1.50 eV - 3.70 eV. It was experimentally established that the absorption spectra have an additional absorption band and its corresponding energy depends on the nature (Cu or Cd) and concentration of the doping atoms. Also, independently on the presence of the dopant, other two absorption bands in the IR region are present.

Research paper thumbnail of OPTICAL AND PHOTOELECTRICAL CHARACTERISTICS OF GaSe (Cu)/OXIDE SEMICONDUCTOR HETEROJUNCTION

Research paper thumbnail of Study of generation-recombination processes of non-equilibrium charge carriers in single crystalline thin GaSe (Cu) films

Journal of Optoelectronics and Advanced Materials

The generation-recombination processes of non-equilibrium charge carriers in undoped and Cu-doped... more 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 a...

Research paper thumbnail of ELLIPSOMETRIC STUDIES OF NANOMETRIC CdS AND CdTe FILMS

Experimental Methods in the Physical Sciences

The thickness of the layers CdS and CdTe grown on the Si, Ge, GaAs was determined from the analys... more The thickness of the layers CdS and CdTe grown on the Si, Ge, GaAs was determined from the analysis of the polarization ellipse of the reflected light from the surfaces of structures thin layers substrate. The thermal treatment of the samples CdS-CdTe in the presence of CdCl 2 leads to the increasing of the crystalline phase from layers.

Research paper thumbnail of INVESTIGATION OF ENERGETIC STATES, DETERMINED BY Cu AND Cd IMPURITY ATOMS, AT SURFACE OF GaS AND GaSe MONOCRYSTALLINE LAYERS

The reflection, absorption, photoconductivity, and thermally stimulated luminescence (TSL) spectr... more The reflection, absorption, photoconductivity, and thermally stimulated luminescence (TSL) spectra of GaS:Cu and GaSe:Cu, Cd single crystals have been studied. As a result of these investigations, the energy diagram of GaS and GaSe crystals after doping was deter- mined.

Research paper thumbnail of <title>Surface structure of CdS layer at the interface of CdS-SnO<formula><inf><roman>2</roman></inf></formula> junction and the diagram of surface states</title>

Advanced Topics in Optoelectronics, Microelectronics, and Nanotechnologies IV, 2009

ABSTRACT The SnO2-CdS type structures with SnO2 film deposited by thermal pirolize in SnCl4-etano... more ABSTRACT The SnO2-CdS type structures with SnO2 film deposited by thermal pirolize in SnCl4-etanol solution were obtained. The CdS film with submicron thickness was obtained in cvasiclosed volume. The transversal section of the SnO2-CdS junction as well as the outer surface of the CdS film was analyzed using the electronic microscope. The density of the crystallization germs in the CdS film was about 1013cm-2. The luminescence spectrum of CdS has been examined. The existence of exciton line (n=1) in reflection and emission spectrum serves as a criteria of crystalline perfection of surface film.

Research paper thumbnail of Structural and optical characteristics of bismuth oxide thin films

Surface Science, 2002

The formation of different phases of Bi-O system during oxidizing process of Bi films from the vi... more The formation of different phases of Bi-O system during oxidizing process of Bi films from the viewpoint of structure characteristics and optical properties, is investigated. As revealed by structure and surface investigations, the thermal oxidation, in air, of Bi films on glass results in polycrystalline and multiphase bismuth oxide films. At substrate-film interface an amorphous oxide layer forms up, to whom surface the growth processes of crystallites belonging to divers phases, with different geometric shapes occur. For nanometric up to submicronic thicknesses, BiO is predominant phase, while in case of micronic films, a-Bi 2 O 3 and Bi 2 O 3 are the main phase components. From absorption curves the band gap values, (E g ¼ 2:29-3:31 eV), for direct transitions, have been determined and an energy gap of $2 eV for amorphous phase was found. Ó

Research paper thumbnail of <title>Optical bistability in GaSe single crystals and ZnTe thin films</title>

ROMOPTO '94: Fourth Conference in Optics, 1995

ABSTRACT By means of two-beam experiments, the transmission properties of highly excited GaSe cry... more ABSTRACT By means of two-beam experiments, the transmission properties of highly excited GaSe crystal of different thicknesses (2 micrometers to 1.5 mm) have been investigated in the fundamental absorption and free exciton region. Induced transmission was observed in the whole considered region for lower pump intensities. Results of bistability in an entire ZnTe thin films are present for the first time.

Research paper thumbnail of Low-temperature Photoluminescence Studies of CdTe Thin Films Deposited on CdS/ZnO/Glass Substrates

MRS Proceedings, 2013

The CdTe photoluminescence spectra of CdTe/CdS/ZnO heterojunctions annealed in the presence of Cd... more The CdTe photoluminescence spectra of CdTe/CdS/ZnO heterojunctions annealed in the presence of CdCl 2 have been analyzed in the 4.7-100K temperature range. The analysis has been performed for laser excitation power between 0.01 mW and 30 mW. The analysis showed that the photoluminescence spectrum in the 1.1-1.6 eV region consists of a defect band (1.437 eV) having complex structure and revealing well contoured LO phonon replicas and bound exciton annihilation in the 1.587-1.593 eV region. The band analysis has been carried out by deconvoluting the spectra. It has been shown that the defect band consists of two elementary bands and their phonon replica. An "unusual" temperature dependence of the defect band has been found.

Research paper thumbnail of A comparative study of (ZnO, In2O3: SnO2, SnO2)/CdS/CdTe/(Cu/)Ni heterojunctions

Thin Solid Films, 2013

ABSTRACT The influence of the manufacturing technology on the structural properties of CdTe and C... more ABSTRACT The influence of the manufacturing technology on the structural properties of CdTe and CdS layers, components of the CdS/CdTe solar cells, has been investigated. CdTe based solar cells have been prepared using glass substrates coated with different transparent conductive oxides (TCOs: SnO2, In2O3: SnO2 (ITO), ZnO:Al, ZnO:Al/i-ZnO).The analysis of the technology combined with various investigation methods allowed to determine optimum deposition parameters for CdS and CdTe for each type of TCO used. X-ray diffraction (XRD) and grazing incidence XRD analysis have been carried out for TCO, CdS, and CdTe layers at different deposition stages before and after annealing in the presence of CdCl2 in air. The reflection spectra in the 100–600 cm− 1 spectral region have been thoroughly studied by using Fourier transform infrared spectroscopy. It was found that (i) the best quality possess CdS and CdTe thin films sequentially deposited on ZnO:Al substrates and that (ii) the pre-treatment defects can be effectively cured and most of the secondary phases can be removed by annealing, while the basic structure of the investigated thin films does not essentially change.

Research paper thumbnail of Optical and photoelectrical properties of GaS and CdTe thin FILMS, components of GaS/CdTe heterojunctions

In the paper, experimental results concerning the absorption and photosensibility spectral depend... more In the paper, experimental results concerning the absorption and photosensibility spectral dependence of GaS and CdTe thin film components of GaS/CdTe heterojunctions are presented. GaS films (d = 0.06 µm -2.8 µm) were deposited onto ITO substrate by laser light pulses. CdTe films (d = 3.6 µm) were deposited onto GaS films by close-spaced sublimation technique. At the fundamental absorption edge, the absorption coefficient of CdTe layers increases of five orders of magnitude in a narrow 40 -100 meV energy range, up to 4 10 4 cm -1 . At room temperature, the energy band of GaS/CdTe heterojunctions photosensitivity is 1.45 eV-2.75 eV, the photocurrent having a constant value up to 2.0 eV photon energy.

Research paper thumbnail of Thin Solid Films 480-481

Research paper thumbnail of BISTABLE OPTIC MODULATORS MADE FROM MONOCRYSTALLINE LAYERS GaSe (Cu)

Fabry-Perot interferometer was constructed on the basis of parallel - slides plates cut off from ... more Fabry-Perot interferometer was constructed on the basis of parallel - slides plates cut off from the GaSe(Cu) single crystals with Cu concentration of 0.05 at%. The thickness of these plates was equal to 5 ÷ 10 μm. Dielectric glass, which consisted of 7 ZnS layers and 7 MgF2 layers with λ/4 thickness, was placed on lateral surfaces of the plates. The reflectance of the glass was equal to ~ 73%. The dependence of interferometer transparency on the intensity of incident radiation with 0.6328 μm wavelength is studied. The threshold intensity, for which periodic pulsations of transmission are observed, is determined from this dependence.

Research paper thumbnail of Non-equilibrium charge carriers generation — recombination mechanisms at the interface of the SnO2/GaSe heterojunction

Thin Solid Films, 2009

The interface of the SnO 2 /GaSe heterojunctions, having SnO 2 layer obtained by different deposi... more The interface of the SnO 2 /GaSe heterojunctions, having SnO 2 layer obtained by different deposition methods have been studied using the photoluminescence and photocurrent spectral distribution. The SnO 2 /GaSe structures are photosensitive in the 1.7 ÷ 3.6 eV spectral range and reveal its maximum value for the heterojunctions with magnetron sputtered SnO 2 layer.

Research paper thumbnail of On the optical properties of bismuth oxide thin films prepared by pulsed laser deposition

Thin Solid Films, 2005

The optical properties of bismuth oxide films prepared by pulsed laser deposition (PLD), absorpti... more The optical properties of bismuth oxide films prepared by pulsed laser deposition (PLD), absorption in the photon energy range 2.50-4.30 eV and optical functions (n, k, e 1 , and e 2 ) in the domain 3.20-6.50 eV, have been investigated. As-prepared films (d=0.05-1.50 Am) are characterized by a mixture of polycrystalline and amorphous phases. The fundamental absorption edge is described by direct optical band-toband transitions with energies 2.90 and 3.83 eV. The dispersion of the optical functions provided values of 4.40-6.25 eV for electron energies of respective direct transitions. In the spectral range 400-1000 nm, bismuth oxide films show a normal dispersion, which can be interpreted in the frame of a single oscillator model. D

Research paper thumbnail of The influence of thermal annealing in presence of CdCl2 on the electrophysical properties of the CdS/CdTe solar cells

Thin Solid Films, 2005

ABSTRACT The investigation of the charge carrier energy states in CdS/CdTe solar cells was based ... more ABSTRACT The investigation of the charge carrier energy states in CdS/CdTe solar cells was based on the studies of absorption and photoconductivity spectral dependencies, quantum efficiency, photoconductivity kinetics measurements at 78 and 300 K. The analysis of the absorption spectra of cadmium telluride (CdTe) films used as a component of SnO2/CdS/CdTe/Ni solar cells, had shown that its heat treatment in CdCl2 leads to the formation of an impurity level localized at ∼20 meV from the top of CdTe valence band. The high photovoltaic properties of the SnO2/CdS/CdTe/Ni solar cells are determined by the presence of the recombination level with a lifetime equal to 180 μs. The heterojunctions heat treatment in CdCl2 leads to the structure defects removal in the semiconductor layers, recrystallization of CdS film and to the formation of CdSxTe1−x (x∼0.95) solutions at the interface.

Research paper thumbnail of Photoelectrical properties of layered GaS single crystals and related structures

Materials Research Bulletin, 2008

The photoconductivity of pure and Cu-doped layered gallium monosulfide (GaS) single crystals, and... more The photoconductivity of pure and Cu-doped layered gallium monosulfide (GaS) single crystals, and of Ni-GaS(Cu)-In and GaS(Cu)-ZnO structures, is investigated. The activation energies of surface states were found as 0.10 eV, 0.40 eV and 17 meV, $400 meV for GaS and GaS(Cu), respectively. Cu acceptor levels are localized at 0.44 eV and 0.52 eV above the valence band of GaS. ZnO-GaS(Cu) heterojunctions show remarkable photosensitivity in the wavelength range of 250-700 nm. #