Replacing lead atoms in halide perovskite materials is of significant importance for the developm... more Replacing lead atoms in halide perovskite materials is of significant importance for the development of environmentally friendly perovskite solar cells. In this paper, we investigated the effect of doping the MAPbI2.6Cl0.4 hybrid perovskite (MA-methyl ammonium) with non-toxic elements, such as alkaline earth metal ions (Mg2+) and transition metal ions (Zn2+). The structural, morphological, and optical properties of the prepared samples were analyzed using X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), and UV-Vis. spectroscopy. Finally, the doped films were used as photoactive layers in solar devices in order to evaluate their photovoltaic performance. Zn proved to be more appropriate to replace partially Pb and films with higher quality were obtained. As a result, the MAPb1-xZnxI2.6Cl0.4 based solar cells have demonstrated a slight improvement of the photovoltaic performances, resulting in a uniform and narrower PCEs (power conversion eff...
High-k La2Hf2O7 traps in insulator layers deposited on Silicon were characterized using temperatu... more High-k La2Hf2O7 traps in insulator layers deposited on Silicon were characterized using temperature dependent I-V, C-V and photocurrent measurements on MIS structures. In addition, the temporal response following a voltage step was used to give insight into the influence of traps on the electrical characteristics of the device. In structures with thicker insulator layers the energy-band diagram is close to the one deduced theoretically from the difference between the work-functions of Al and Si. However, at temperatures lower than 260 K the C-V curves move towards positive voltages due to the increased number of negatively charged centers. We attribute the increase of the concentration of negatively charged centers that we observe when the temperature is decreased to the presence of strain in the structure.
Magnetic, Ferroelectric, and Multiferroic Metal Oxides, 2018
Abstract The concept of graded ferroelectrics became of significant interest for researchers work... more Abstract The concept of graded ferroelectrics became of significant interest for researchers working in the field of ferroelectric materials and related applications during the 1990s, when a number of published papers reported a series of intriguing phenomena observed in this type of structure. Among these are the shift of the hysteresis loop along the polarization axis, the presence of a giant effective pyroelectric coefficient, and the possibility of using the graded structures as ferroelectrics similar to semiconductor p–n junctions. Some pioneering experimental work was performed on simple structures composed of two layers with different values of polarization, called also ferroelectric bimorph. During the years, the interest for graded structures remained significant both from the point of view of the basic research as well as considering the potential applications in electronics, sensing, and energy. The concept of graded ferroelectric structures includes all structures in which a polarization gradient is present. This gradient can be obtained in several ways, such as (1) producing a concentration gradient along the direction normal to the electrodes; (2) producing a temperature gradient between the opposite electrodes of the capacitor; and (3) producing a strain gradient along the direction normal to the electrodes.
Single-phase Ce3+-doped BaTiO3 powders described by the nominal formula Ba1−xCexTi1−x/4O3 with x ... more Single-phase Ce3+-doped BaTiO3 powders described by the nominal formula Ba1−xCexTi1−x/4O3 with x = 0.005 and 0.05 were synthesized by the acetate variant of the sol-gel method. The structural parameters, particle size, and morphology are strongly dependent on the Ce3+ content. From these powders, dense ceramics were prepared by conventional sintering at 1300 °C for 2 h, as well as by spark plasma sintering at 1050 °C for 2 min. For the conventionally sintered ceramics, the XRD data and the dielectric and hysteresis measurements reveal that at room temperature, the specimen with low cerium content (x = 0.005) was in the ferroelectric state, while the samples with significantly higher Ce3+ concentration (x = 0.05) were found to be in the proximity of the ferroelectric–paraelectric phase transition. The sample with low solute content after spark plasma sintering exhibited insulating behavior, with significantly higher values of relative permittivity and dielectric losses over the entir...
Shallow defect levels in floating zone (FZ) and diffusion oxygenated FZ (DOFZ) silicon, before an... more Shallow defect levels in floating zone (FZ) and diffusion oxygenated FZ (DOFZ) silicon, before and after irradiation with a 60Co gamma-source up to 300 Mrad, have been studied by thermally stimulated currents (TSC) and deep level transient spectroscopy (DLTS) in the temperature range 4.2-110 K. Besides vacancy oxygen (VO) and interstitial-substitutional carbon (CiCs) emissions, several TSC peaks have been observed. A trap with an activation energy of 11 meV has been observed at 6 K only in irradiated DOFZ. Two hole traps at 80 meV and 95 meV have been observed both in irradiated FZ and DOFZ, while a trap at 100 meV, related to an interstitial-oxygen (IO2) complex, has been revealed only in irradiated DOFZ. A TSC peak close to 24 K has been resolved into two components, whose concentrations are independent of irradiation fluence: a trap at 55 meV and a level which remains charged after emission at 80 meV. Our measurements confirm the formation, only in DOFZ, of a radiation induced do...
The rectifying properties of Nb:SrTiO3-Bi1−xGdxFeO3-Pt structures (x = 0, 0.05, 0.1) displaying d... more The rectifying properties of Nb:SrTiO3-Bi1−xGdxFeO3-Pt structures (x = 0, 0.05, 0.1) displaying diode-like behavior were investigated via current-voltage characteristics at different temperatures. The potential barrier was estimated for negative polarity assuming a Schottky-like thermionic emission with injection controlled by the interface and the drift controlled by the bulk. The height of the potential barrier at the Nb:SrTiO3-Bi1−xGdxFeO3 interface increases with Gd doping. The results are explained by the partial compensation of the p-type conduction due to Bi vacancies with Gd doping in addition to the shift of the Fermi level towards the middle of the bandgap with increasing dopant concentration.
The leakage current was studies in epitaxial ferroelectric Pb(Zr0.52Ti0.48)O3 layer with common S... more The leakage current was studies in epitaxial ferroelectric Pb(Zr0.52Ti0.48)O3 layer with common SrRuO3 bottom electrode and different metals as top contacts (SrRuO3, Pt, Ir, Ru). It was found that the dominant conduction mechanism in the 200-350 K temperature range and for voltages significantly larger than the coercive value is the thermionic emission governed by the Schottky-Simmons equation. The height of the potential barriers was estimated and was found that this is about the same for negative and positive voltage polarities. No correlation was found between the height of the potential barriers for different top contacts and the work function difference between the bottom and top electrodes. The results suggest that the potential barrier is controlled by the polarization charges in a similar way to the one reported for Pb(Zr0.2Ti0.8)O3 and BaTiO3 epitaxial films with bottom SrRuO3 electrode and different metals as top contacts. It was also found that above 350 K the conduction ...
The paper presents progress in infrared (IR) detector technologies during two hundred history of ... more The paper presents progress in infrared (IR) detector technologies during two hundred history of their development. Classification of two types of infrared detectors (photon detectors and thermal detectors) is done on the basis of their principle of operation. The overview of infrared systems and detectors is presented. Recent progress in different IR technologies is described from a historical point of view. Discussion is concentrated mainly on current and the most rapidly developing detectors: HgCdTe heterostructure photodiodes, quantum well AlGaAs/GaAs photoresistors, and thermal detectors. The outlook for near-future trends in IR technologies is also presented.
Replacing lead atoms in halide perovskite materials is of significant importance for the developm... more Replacing lead atoms in halide perovskite materials is of significant importance for the development of environmentally friendly perovskite solar cells. In this paper, we investigated the effect of doping the MAPbI2.6Cl0.4 hybrid perovskite (MA-methyl ammonium) with non-toxic elements, such as alkaline earth metal ions (Mg2+) and transition metal ions (Zn2+). The structural, morphological, and optical properties of the prepared samples were analyzed using X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), and UV-Vis. spectroscopy. Finally, the doped films were used as photoactive layers in solar devices in order to evaluate their photovoltaic performance. Zn proved to be more appropriate to replace partially Pb and films with higher quality were obtained. As a result, the MAPb1-xZnxI2.6Cl0.4 based solar cells have demonstrated a slight improvement of the photovoltaic performances, resulting in a uniform and narrower PCEs (power conversion eff...
High-k La2Hf2O7 traps in insulator layers deposited on Silicon were characterized using temperatu... more High-k La2Hf2O7 traps in insulator layers deposited on Silicon were characterized using temperature dependent I-V, C-V and photocurrent measurements on MIS structures. In addition, the temporal response following a voltage step was used to give insight into the influence of traps on the electrical characteristics of the device. In structures with thicker insulator layers the energy-band diagram is close to the one deduced theoretically from the difference between the work-functions of Al and Si. However, at temperatures lower than 260 K the C-V curves move towards positive voltages due to the increased number of negatively charged centers. We attribute the increase of the concentration of negatively charged centers that we observe when the temperature is decreased to the presence of strain in the structure.
Magnetic, Ferroelectric, and Multiferroic Metal Oxides, 2018
Abstract The concept of graded ferroelectrics became of significant interest for researchers work... more Abstract The concept of graded ferroelectrics became of significant interest for researchers working in the field of ferroelectric materials and related applications during the 1990s, when a number of published papers reported a series of intriguing phenomena observed in this type of structure. Among these are the shift of the hysteresis loop along the polarization axis, the presence of a giant effective pyroelectric coefficient, and the possibility of using the graded structures as ferroelectrics similar to semiconductor p–n junctions. Some pioneering experimental work was performed on simple structures composed of two layers with different values of polarization, called also ferroelectric bimorph. During the years, the interest for graded structures remained significant both from the point of view of the basic research as well as considering the potential applications in electronics, sensing, and energy. The concept of graded ferroelectric structures includes all structures in which a polarization gradient is present. This gradient can be obtained in several ways, such as (1) producing a concentration gradient along the direction normal to the electrodes; (2) producing a temperature gradient between the opposite electrodes of the capacitor; and (3) producing a strain gradient along the direction normal to the electrodes.
Single-phase Ce3+-doped BaTiO3 powders described by the nominal formula Ba1−xCexTi1−x/4O3 with x ... more Single-phase Ce3+-doped BaTiO3 powders described by the nominal formula Ba1−xCexTi1−x/4O3 with x = 0.005 and 0.05 were synthesized by the acetate variant of the sol-gel method. The structural parameters, particle size, and morphology are strongly dependent on the Ce3+ content. From these powders, dense ceramics were prepared by conventional sintering at 1300 °C for 2 h, as well as by spark plasma sintering at 1050 °C for 2 min. For the conventionally sintered ceramics, the XRD data and the dielectric and hysteresis measurements reveal that at room temperature, the specimen with low cerium content (x = 0.005) was in the ferroelectric state, while the samples with significantly higher Ce3+ concentration (x = 0.05) were found to be in the proximity of the ferroelectric–paraelectric phase transition. The sample with low solute content after spark plasma sintering exhibited insulating behavior, with significantly higher values of relative permittivity and dielectric losses over the entir...
Shallow defect levels in floating zone (FZ) and diffusion oxygenated FZ (DOFZ) silicon, before an... more Shallow defect levels in floating zone (FZ) and diffusion oxygenated FZ (DOFZ) silicon, before and after irradiation with a 60Co gamma-source up to 300 Mrad, have been studied by thermally stimulated currents (TSC) and deep level transient spectroscopy (DLTS) in the temperature range 4.2-110 K. Besides vacancy oxygen (VO) and interstitial-substitutional carbon (CiCs) emissions, several TSC peaks have been observed. A trap with an activation energy of 11 meV has been observed at 6 K only in irradiated DOFZ. Two hole traps at 80 meV and 95 meV have been observed both in irradiated FZ and DOFZ, while a trap at 100 meV, related to an interstitial-oxygen (IO2) complex, has been revealed only in irradiated DOFZ. A TSC peak close to 24 K has been resolved into two components, whose concentrations are independent of irradiation fluence: a trap at 55 meV and a level which remains charged after emission at 80 meV. Our measurements confirm the formation, only in DOFZ, of a radiation induced do...
The rectifying properties of Nb:SrTiO3-Bi1−xGdxFeO3-Pt structures (x = 0, 0.05, 0.1) displaying d... more The rectifying properties of Nb:SrTiO3-Bi1−xGdxFeO3-Pt structures (x = 0, 0.05, 0.1) displaying diode-like behavior were investigated via current-voltage characteristics at different temperatures. The potential barrier was estimated for negative polarity assuming a Schottky-like thermionic emission with injection controlled by the interface and the drift controlled by the bulk. The height of the potential barrier at the Nb:SrTiO3-Bi1−xGdxFeO3 interface increases with Gd doping. The results are explained by the partial compensation of the p-type conduction due to Bi vacancies with Gd doping in addition to the shift of the Fermi level towards the middle of the bandgap with increasing dopant concentration.
The leakage current was studies in epitaxial ferroelectric Pb(Zr0.52Ti0.48)O3 layer with common S... more The leakage current was studies in epitaxial ferroelectric Pb(Zr0.52Ti0.48)O3 layer with common SrRuO3 bottom electrode and different metals as top contacts (SrRuO3, Pt, Ir, Ru). It was found that the dominant conduction mechanism in the 200-350 K temperature range and for voltages significantly larger than the coercive value is the thermionic emission governed by the Schottky-Simmons equation. The height of the potential barriers was estimated and was found that this is about the same for negative and positive voltage polarities. No correlation was found between the height of the potential barriers for different top contacts and the work function difference between the bottom and top electrodes. The results suggest that the potential barrier is controlled by the polarization charges in a similar way to the one reported for Pb(Zr0.2Ti0.8)O3 and BaTiO3 epitaxial films with bottom SrRuO3 electrode and different metals as top contacts. It was also found that above 350 K the conduction ...
The paper presents progress in infrared (IR) detector technologies during two hundred history of ... more The paper presents progress in infrared (IR) detector technologies during two hundred history of their development. Classification of two types of infrared detectors (photon detectors and thermal detectors) is done on the basis of their principle of operation. The overview of infrared systems and detectors is presented. Recent progress in different IR technologies is described from a historical point of view. Discussion is concentrated mainly on current and the most rapidly developing detectors: HgCdTe heterostructure photodiodes, quantum well AlGaAs/GaAs photoresistors, and thermal detectors. The outlook for near-future trends in IR technologies is also presented.
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