One-dimensional femtosecond laser-induced periodic surface structures (LIPSS) were formed on amorphous silicon (a-Si) films doped with phosphorus (n-a-Si) and boron (p-a-Si). The formed LIPSS ridges are directed orthogonally to the laser polarization and their period decreases from 1.1 ± 0.1 µm to 0.84 ± 0.07 µm for p-a-Si and from 1.06 ± 0.03 to 0.98 ± 0.01 for n-a-Si when the number of laser pulses per unit area increases from 30 to 120. Raman spectra analysis indicated nonuniform nanocrystallization of the irradiated films, which have a composite structure of amorphous matrix containing nanocrystalline Si phase with volume fraction decreasing with depth from ~80 to ~40% for p-a-Si and from ~20 to ~10% for n-a-Si. Observed in plane conductivity anisotropy of up to 1 order for irradiated films may be explained by the LIPSS depolarizing effect, excessive ablation of the film between LIPSS ridges, as well as anisotropic crystalline phase distribution within the film.

The effect of annealing of organometallic perovskite CH3NH3PbI3 film on its electrical, photoelectric, and optical properties is studied. It was shown that annealing at Та>140 °C leads to the two-phase structure formation consisting of perovskite and lead iodide, the relative content of which depends on the annealing conditions, in particular, on its temperature. The PbI2 formation in the perovskite structure leads to a decrease in the conductivity and photoconductivity of the material. Our studies indicate the possibility of forming planar structures consisting of semiconductor materials with various values of the band gap: 1.6 eV (CH3NH3PbI3) and 2.4 eV (PbI2).

The effect of annealing of a CH3NH3PbI3 organometallic perovskite film on its electrical, photoelectrical, and optical properties is studied. It is shown that annealing at the temperature Ta > 140°C results in the formation of a two-phase structure consisting of perovskite and lead iodide, whose relative content depends on the conditions of annealing, specifically, on the annealing temperature. The formation of PbI2 in the perovskite structure yields a decrease in the conductivity and photoconductivity of the material. The studies suggest the possibility of the formation of planar structures composed of semiconductor materials with different band gaps, 1.6 eV (CH3NH3PbI3) and 2.4 eV (PbI2).

Photoelectric characteristics of photodetectors of the type of a photoresistor based on microcrystalline films of the organometallic perovskite CH 3 NH 3 PbI 3 with gold and aluminum contacts have been studied. The maximum photosensitivity of the photodetectors was 30 A/W. The buildup and decay times of the photoconductivity were in the range from 2.6 to 25.5 μs.

The photoelectric characteristics of photoresistance type photodetectors based on microcrystalline films of organometallic perovskite CH3NH3PbI3 with gold and aluminum contacts were investigated. The maximum photosensitivity of the photodetectors was 30 A / W. The rise and fall times of photoconductivity ranged from 2.7 to 15.3 μs.

Abstract A significant effect of the environment (vacuum, air) on the results of measurements of CH3NH3PbI3 films conductivity and photoconductivity is shown. It was found that prolonged illumination with white light does not change the value of CH3NH3PbI3 interband photoconductivity (hν > 1.6 eV), but leads to a metastable increase in the photoconductivity near the quantum energy hν ≈ 1.2 eV. This indicates a photoinduced creation or filling of nonrecombination localized states, located at an energy distance of 1.2 eV from the transport level of nonequilibrium charge carriers.

The effect of temperature on the photoconductivity and its spectral dependence for thin films of organometallic CH3NH3PbI3 perovskite is studied. The measurements performed at temperatures below room temperature reveal the features of the change in the photoconductivity with temperature in the region of the phase transition from the tetragonal to orthorhombic structure (140–170 K). On the basis of analysis of the effect of temperature on the nature of the change in the spectral dependences of the photoconductivity in the phase-transition region, mechanisms are proposed, which clarify the observed change in the photoconductivity.

In this work, the effect of temperature on photoconductivity and its spectral dependence for thin films of metal-organic perovskite CH3NH3PbI3 was studied. Measurements carried out in the temperature region below room temperature revealed specific features of photoconductivity variation with temperature in the phase transition region from the tetragonal to orthorhombic structure (140–170 K). Based on the analysis of the effect of temperature on the spectral dependences of photoconductivity in the region of the phase transition mechanisms are proposed that determine the observed change in photoconductivity

Two types of independent anisotropic structures have been formed simultaneously in amorphous hydrogenated films by applying a femtosecond laser pulse to them, i.e., a structure with a period of several micrometers to several tens of micrometers and a structure with a period of several hundred nanometers. The formation mechanisms of these strictures are different, which allows us to orient them relative to each other in a desirable way. Both structures independently influence the optical properties of the modified films, which causes the diffraction of transmitted light and making the films polarization-sensitive. The conductivity of the modified films correlates with the mutual orientation of the anisotropic structures, whereas no interrelation between the photoconductivity and optical performance of the modified films has been observed.

Поступило в Редакцию 22 июня 2016 г

Halide perovskites are widely studied due to their potential applications in solar cells. Despite the remarkable success in increasing perovskite solar cell efficiency, the underlying photophysical processes remain unclear. To cover this gap, we studied temperature, spectral, and light intensity dependence of photoconductivity of CH3NH3PbI3 films in the planar contact configuration. We observed non-monotonic behavior of the photoconductivity temperature dependence: a power-law decrease with increasing temperature at the temperatures below 185 K and close to exponential growth above this temperature. Spectral and light intensity dependences of photoconductivity allowed us to postulate that phase transition between tetragonal and orthorhombic structures and a change in the recombination channel are unlikely to be the reasons for abrupt change in photoconductivity behavior. Charge carrier mobility is proposed to be responsible for unusual photoconductivity changes with temperature.

Ultrafast laser processing of semiconductors is a rapidly developing field of material science at the moment. In particular, femtosecond laser crystallization of amorphous hydrogenated silicon thin films has a big potential in photovoltaics. However laser treatment causes dehydrogenation process which decreases materials' photosensitivity and thus limiting its application for optoelectronics. In present paper we studied photoelectric properties of laser-modified amorphous silicon films. Two different hydrogenation procedures were employed to restore films' hydrogen content: keeping in hydrogen plasma and in high-pressure hydrogen atmosphere. The effectiveness of applied procedures for increasing materials' photosensitivity is discussed.

Amorphous and microcrystalline hydrogenated silicon is an important material in modern thinfilm electronics. In some cases, the electrical parameters of silicon film samples depend on the ambient environment, in particular, the air. In this work we studied the effect of air exposure on the electrical properties of two-phase silicon films with a volume fraction of the crystalline phase of 0 to 80%. It was shown that the change in the conductivity of the two-phase films that were exposed to the air atmosphere depends on the proportion between the amorphous and microcrystalline phases that form the film microstructure. The use of two differing methods for film manufacturing allowed us to qualitatively evaluate how the conductivity of the films with a nonuniform structure across the thickness is affected by gas adsorption from air onto the film surface. Air exposure of the samples with a small amount of the crystalline phase located near the film surface leads to the specific features of temperature dependence of their conductivity.

Femtosecond laser processing of hydrogenated amorphous silicon is a perspective method for thin film solar cells production. It allows to make local crystallization and surface texturing of the films which results in the enhancement of their light absorption and stability of parameters. Thickness of modified material depends strongly on a laser wavelength. However laser wavelength affects also other properties of the film. Therefore here we study structure, surface morphology and photoelectric properties of hydrogenated amorphous silicon films treated by femtosecond laser pulses of different photon energies, namely above, around and below the mobility gap of amorphous silicon.