Specific features of amorphous silicon layers grown by plasma-enhanced chemical vapor deposition with tetrafluorosilane

Hydrogenated amorphous silicon layers with crystalline nanoparticles have been produced by plasma-enhanced chemical vapor deposition, with tetrafluorosilane added to the gas mixture. The photoluminescence kinetics and photoelectric properties of structures based on these layers have been studied. The structures have a substantial photoresponse efficiency in the visible spectral range, with the position of the photoresponse maximum dependent on the applied bias.     

Energy distribution of localized states in amorphous hydrogenated silicon

A new method for determining the spectral dependence of the optical-absorption coefficient in amorphous hydrogenated silicon is suggested. The method is based on the analysis of spectral and temperature dependences of transient photoconductivity in this material. Energy distribution of localized states involved in recombination of nonequilibrium holes was calculated.     

The influence of erbium on electrical and photoelectric properties of amorphous silicon produced by radio-frequency silane decomposition

Thermal evaporation of tris(2,2,6,6-tetramethyl-2,5-heptadionato) Er(III) inside the plasma gap was used to introduce erbium into amorphous hydrogenated silicon (a-Si:H) obtained by radio-frequency silane decomposition. The samples obtained had a pronounced layered structure due to exhaustion of the erbium source. The layer nearest to the substrate was enriched with erbium, oxygen, and carbon; gave rise to luminescence with a wavelength of 1.535 µm characteristic of ⁴ I _13/2 → ⁴ I _15/2 intra-atomic transitions of erbium; and contained a large number of defects. The top layer contained much fewer defects, was close to undoped a-Si:H in the photoelectric characteristics, and was responsible for photoconductivity in the samples obtained. The experimental data are analyzed in the context of the models for doping of a-Si:H with Er with the resulting emergence of n-type conduction and formation of heterojunction as the film grows.     

Structure and properties of a-Si:H films grown by cyclic deposition

Amorphous hydrogenated silicon films obtained by cyclic deposition with intermediate annealing in hydrogen plasma were studied. a-Si:H films deposited under optimal conditions are photosensitive (photoconductivity to dark conductivity ratio σ_ph/σ_d is as high as 10⁷ under 20 mW cm^?2 illumination in the visible region of the spectrum) and have an optical gap (E _g ) and activation energy of conductivity (E _a ) of 1.85 and 0.91 eV, respectively. Electron microscopy studies revealed a clearly pronounced layered structure of a-Si:H films and the presence of nanocrystalline inclusions in the amorphous matrix.     

Membrane-electrode assemblies with high specific power based on functionalized carbon nanotubes

It is demonstrated that the efficiency of catalysis and platinum usage in electrochemical energy converters can be improved by employing chemically functionalized multiwalled carbon tubes. On this basis, membrane-electrode assemblies for air-hydrogen fuel cells with specific powers up to 581 mW/cm² have been obtained.     

Photoinduced degradation of α-Si:H/μc-Si:H tandem photoconvertes at elevated temperatures

Photoinduced degradation of tandem photoconverters with the structure α-Si:H/μc-Si:H and initial efficiency of 10.5% at temperatures of 298, 328, and 353 K is experimentally studied. It has been found that, at a temperature of 298 K, the efficiency of the photoconverters decreases by 1.0–1.2% during long light exposure, while an increase in temperature to 328 K leads to a decrease in efficiency to 0.2%; at a temperature of 353 K, no degradation is observed. To explain these results, a modified H-collision model was used. Thermal-activation energy has been determined for the process that hampers the growth of dangling (ruptured) bonds in the i-α-Si:H layer.     

Erbium impurity atoms in silicon

It is shown using ¹⁶⁹Er(¹⁶⁹Tm) Mössbauer emission spectroscopy that the photoluminescent centers in crystalline erbium-doped silicon are [Er-O] clusters and that the local symmetry of the Er³⁺ ions in these clusters is similar to that in Er₂O₃. The photoluminescent centers in amorphous hydrogenated erbium-doped silicon are clusters, whose local structure also corresponds to erbium oxide.     

Heterogeneity and photoconductivity kinetics in amorphous hydrogenated silicon

A model of the decay kinetics of photoconductivity in amorphous hydrogenated silicon, in which recombination of excess carriers is assumed to occur via tunnelling, is proposed. It is shown that study of the decay shape after flash illumination can be a very effective way to detect structural inhomogeneities in amorphous or disordered semiconductors. Fiz. Tekh. Poluprovodn. 32, 1266–1268 (October 1998)     

Investigations of CuFeS<Subscript>2</Subscript> semiconductor mineral from ocean rift hydrothermal vent fields by Cu NMR in a local field

The results of investigating natural samples of chalcopyrite mineral CuFeS₂ from massive oceanic sulfide ores of the Mid-Atlantic ridge by the ⁶³Cu nuclear magnetic resonance (NMR ⁶³Cu) in a local field at room temperature are presented. The significant width of the resonance lines found in the ⁶³Cu NMR spectrum directly testifies to a wide distribution of local magnetic and electric fields in the investigated chalcopyrite samples. This distribution can be the consequence of an appreciable deviation of the structure of the investigated chalcopyrite samples from the stoichiometric one. The obtained results show that the pulsed ⁶³Cu NMR can be an efficient method for studying the physical properties of deep-water polymetallic sulfides of the World Ocean.     

Photosensitivity of a-C:H/c-Si heterojunctions

Layers of a-C:H were grown on c-Si wafers by the glow discharge method in a CH₄ + Ar gaseous mixture. The electrical and photoelectric properties of a-C:H/c-Si heterojunctions were studied. It was found that the heterojunctions display rectification and broad-band photovoltaic effects. It is shown that the polarization sensitivity in these structures occurs at an oblique incidence of linearly polarized light under the illumination of the surface coated with a-C:H layers. The observed oscillations in the spectrum of the coefficient of induced photopleochroism are attributed to the interference of light in these layers.