P. A. Forsh

Visible luminescence from hydrogenated amorphous silicon modified by femtosecond laser radiation

Visible luminescence is observed from the composite of SiO2 with embedded silicon nanocrystallites produced by femtosecond laser irradiation of hydrogenated amorphous silicon (a-Si:H) film in air. The photoluminescence originates from the defect states at the interface between silicon crystallites and SiO2 matrix. The method could be used for fabrication of luminescent layers to increase energy conversion of a-Si:H solar cells.

Effect of the femtosecond laser treatment of hydrogenated amorphous silicon films on their structural, optical, and photoelectric properties

The effect of the femtosecond laser treatment of hydrogenated amorphous silicon (a-Si:H) films on their structural, optical, and photoelectric properties is studied. Under the experimental conditions applied in the study, laser treatment of the film with different radiation intensities induces structural changes that are nonuniform over the film surface. An increase in the radiation intensity yields an increase in the contribution of the nanocrystalline phase to the structure, averaged over the sample surface, as well as an increase in the conductance and photoconductance of the samples. At the same time, for all of the samples, the absorption spectrum obtained by the constant-photocurrent method has a shape typical for those of amorphous silicon. Obtained results indicate the possibility of a-Si:H films photoconductance increase by femtosecond pulse laser treatment.

Photoconductivity of two-phase hydrogenated silicon films

Electrical, photoelectric, and optical properties of hydrogenated amorphous silicon films with various ratios between the nanocrystalline and amorphous phases in the structure of the material have been studied. On passing from an amorphous to a nanocrystalline structure, the room-temperature conductivity of the films increases by more than five orders of magnitude. With increasing fraction of the nanocrystalline component in the film structure, the steady-state photoconductivity varies nonmonotonically and is determined by the variation in the carrier mobility and lifetime. Introduction of a small fraction of nanocrystals into the amorphous matrix leads to a decrease in the absorption in the defect-related part of the spectrum and, accordingly, to a lower concentration of dangling bonds, which are the main recombination centers in amorphous hydrogenated silicon. At the same time, the photoconductivity in these films becomes lower, which may be due to appearance of new centers that are related to nanocrystals and reduce the lifetime of nonequilibrium carriers.

Conductivity of nanocrystalline ZnO(Ga)

Nanocrystalline zinc-oxide powders containing different proportions of gallium, ZnO(Ga), are synthesized by coprecipitation from aqueous solutions followed by annealing at 250°C. The dependence of the conductance of the samples on the Ga content is found to be non-monotonous. The temperature dependences of the conductance are studied. The introduction of a low Ga content (0.33–0.50 at %) induces a decrease in the activation energy and the height of the effective potential barrier between nanocrystallites compared to the corresponding parameters of ZnO. Then, as the Ga content is increased, these parameters increase. The data obtained in the study are interpreted within the context of the model of an inhomogeneous semiconductor with large-scale potential fluctuations.

Alternating current conductivity of anisotropically nanostructured silicon

The frequency dependences of the conductivity and capacitance of anisotropic porous silicon prepared by electrochemical etching of single-crystal p-Si (110) wafers were studied. It was found that the conductivity in the direction of the largest size of silicon nanocrystals is much higher than in the direction of their smallest size in the entire frequency (5 Hz-13 MHz) and temperature (170–370 K) ranges under study. An analysis of experimental data showed that the major cause of the electrical transport anisotropy is the anisotropy of silicon nanocrystals forming the samples of porous silicon under study.

Features of the structure and defect states in hydrogenated polymorphous silicon films

The structural and electronic properties of thin hydrogenated polymorphous silicon films obtained by plasma-enhanced chemical vapor deposition from hydrogen (H2) and monosilane (SiH4) gas mixture have been studied by means of transmission electron microscopy, electron paramagnetic resonance (EPR) spectroscopy, and Raman spectroscopy. It has been established that the studied films consist of the amorphous phase containing silicon nanocrystalline inclusions with the average size on the order of 4–5 nm and the volume fraction of 10%. A signal was observed in the hydrogenated polymorphous silicon films during the EPR investigation that is attributed to the electrons trapped in the conduction band tail of microcrystalline silicon. It has been shown that the introduction of a small fraction of nanocrystals into the amorphous silicon films nonadditively changes the electronic properties of the material.

A study of the sensitivity of nanocrystalline indium oxide with various sizes of nanocrystals to nitrogen dioxide

The influence of NO2 adsorption on the electric conductance of the nanocrystalline indium oxide with various sizes of nanocrystals has been investigated. When the nanocrystal size decreases, the sensitivity (the ratio of the In2O3 conductance in the air and the conductance after NO2 adsorption) grows at first but then declines. An explanation for the nonmonotonous behavior of the sensitivity is offered.

Charge carrier transport in indium oxide nanocrystals

Nanocrystalline indium oxide samples with various sizes of nanocrystals are synthesized by the sol-gel method. The minimal and maximal average sizes of nanocrystals are 7–8 and 18–20 nm, respectively. An analysis of conductivity measured at dc and ac signals in a wide temperature range (T = 50–300 K) shows that the transport of charge carriers at high temperatures takes place over the conduction band, while in the low-temperature range, the hopping mechanism with a varying jump length over localized states is observed.

Specific features of electrical transport in anisotropically nanostructured silicon

AbstractElectrical transport in layers of porous silicon obtained by electrochemical etching of (110)-oriented single-crystal silicon wafers of p type was studied. It was found that the lateral conductivity and photoconductivity of the layers along the