Semiconductors

Nanocrystalline silicon films formed using laser ablation of silicon targets were studied using electron spin resonance. The measurements were performed in the X band with modulation of the magnetic field at a frequency of ∼100 kHz at temperatures of 300 and 77 K. Two types of spectra were observed. The first type of spectra is related to the high concentration of dangling silicon bonds in Si nanocrystals and SiOx sheaths of nanocrystals and are inherent in nanocrystalline silicon (nc-Si) films that do not exhibit photoluminescence in the visible region of the spectrum. The second type of spectra is related to the presence of E′ centers, nonbridging oxygen hole centers (NBOHC), and peroxide radicals and is characteristic of films with photoluminescence in the visible region of the spectrum, which indicates that high-barrier SiO2 layers exist in these films. An increase in the photoluminescence intensity and a decrease in the signal of electron spin resonance were observed in porous nc-Si films exposed to atmospheric air for a long time.

A model of the formation of donor centers introduced by a combined implantation of Er+ and O+ ions into silicon with subsequent thermal annealing is developed. These centers are multiparticle erbium-oxygen complexes ErOn with n≥4. The competing process of formation of electrically inactive oxygen clusters is taken into account. The model makes it possible to describe the dependence of the activation coefficient for the donor centers on the implantation dose of oxygen ions and, also, the effects of the oxygen ion implantation and annealing temperature on the concentration profiles of the donor centers.

For detecting low-intensity optical radiation, multielement avalanche photodetectors, which are called silicon photomultiplier tubes, are increasingly used. However, not all characteristics of these photodetectors have been studied in detail; for example, there is no information on the effect of the supply voltage on the dynamic range. For studying the dynamic range, prototypes of silicon photoelectronic multipliers with a p+–p–n+ structure produced by OAO Integral (Belarus), as well as commercially available photomultipliers Ketek PM 3325 and ON Semi FC 30035, are used as the objects of investigation. It is found that an increase in the supply voltage leads to a decrease in the critical and threshold intensities. It is shown that the dependence of the dynamic range on the supply voltage has a peak. In photodetectors based on silicon photomultiplier tubes, for providing the peak dynamic range of detection, it is necessary to select the photodetector supply voltages corresponding to this peak. The results obtained can find application in developing and designing the devices and optical-radiation detectors based on silicon photomultiplier tubes.

A rigorous analytic theory of the blocking state of electrostatically contolled thyristors and transistors and a shallow planar gate of arbitrary width is constructed in the model with a completely depleted base. Formulas are obtained for the subthreshold currents and blocking factor g as functions of the electrode potentials and device parameters: source and gate widths and thickness and doping of the base. It is shown that sufficiently heavy doping not only influences the parameters of the current-voltage characteristics and the factor g but it also changes the qualitative form of the current-voltage characteristic near threshold.

Individual small particles consisting of an insulating core and a metal shell exhibit more intricate behavior when exposed to electromagnetic radiation than continuous metal particles. A composite medium containing a large number of such particles is therefore bound to have new optical properties. If the inclusions are small relative to the wavelength of electromagnetic radiation, the optical characteristics of an inhomogeneous medium can be estimated from its effective permittivity. On the basis of the generalized effective field approximation, a formula is derived to calculate the effective dielectric characteristics of a matrix composite containing spherical inclusions with shells. The formula can be considered a generalization of the classical Maxwell–Garnett formula for a matrix medium with inhomogeneous inclusions consisting of anisotropic cores and isotropic shells. Using the formula, the frequency dependences of the real and imaginary parts of the effective permittivity in the 0.282–0.855 μm range of wavelengths are calculated for a composite consisting of an α-quartz matrix and spherical nanoinclusions with α-quartz cores and silver shells. The dependences are obtained for different relative volume fractions of cores in the inclusions and of inclusions in the composite. The frequency dependences of the refractive index, the extinction coefficient of the composite, and the transmittance and reflectance of a thin composite film are calculated for the range of wavelengths indicated above. It is shown that inclusions with metal shells in a matrix composite result in an additional plasmon resonance, compared to a composite containing all-metal inclusions. With a matrix composite, the additional plasmon resonance is observed at a wavelength of 0.33–0.34 μm in the ultraviolet range and is much less intense than the principal plasmon resonance. The additional plasmon resonance is responsible for the very low transmittance of a composite film in the ultraviolet region. At a constant volume fraction of inclusions in the composite, an increase in the volume fraction of the cores in them shifts the principal plasmon resonance to longer wavelengths and lowers its intensity.

The effect of oxygen on the intensity of erbium photoluminescence at λ=1.54 µm in amorphous a-SiOx:H(Er) films formed by dc magnetron sputtering was studied. The oxygen content in the gaseous phase ranged from 0.1 to 12 mol %, with other parameters of deposition remaining constant. Analysis of an a-Si:(H, Er, O) system showed that the range of homogeneity of amorphous a-SiOx:H(Er) is retrograde (T=const). The range of homogeneity can be conventionally divided into two portions, each of which should contain either of two differently charged [Er-O] n− and [Er-O-Si-O] m− clusters (m>n). This inference is confirmed experimentally: in the range of oxygen concentrations amounting to 5.5–8 mol % in the plasma, unusual associative processes take place probably directly above the growing film surface; these processes are caused by the appearance of [Er-O-Si-O] m− clusters in the plasma and at the surface. It is these processes that account for the intensification of erbium photoluminescence as the oxygen content increases above 5.5 mol %.

Experimental studies of fullerenes at the department of experimental physics, St. Petersburg State Technical University, are reviewed. These studies were performed under the guidance of Professor V.F. Masterov, doctor of mathematics and physics. Primary attention is paid to the studies of the weak-superconductivity effect detected in copper-containing fullerene structures.

Comparative analysis of the influence of thermal annealing on Ge/Au/Ni-, Ge/Au/Ti/Au-, and Ge/Au/Ni/Ti/Au-based ohmic contacts and Ti/Au-based Schottky contacts deposited on an n-GaAs (100) surface treated and nontreated in (NH4)2S aqueous solution have been performed. Annealing conditions for ohmic contacts are found that lead to a decrease in the specific contact resistance of sulfur-treated samples by a factor of 2.5–15 in comparison with the nontreated samples. Optimal annealing conditions are also determined for sulfur-treated GaAs samples with Schottky contacts, which make it possible to reduce the ideality factor and increase the barrier height and the breakdown voltage with respect to the nontreated samples.

Technology for the infiltration of zinc oxide into a three-dimensional opal lattice using chemical deposition from a solution was developed. Samples of ZnO-opal composites, whose luminescence at room temperature mainly occurs in the ultraviolet spectral range, were obtained. The filling ratio was monitored by two different techniques: (i) checking the increase in the mass of the sample and (ii) checking the shift of the peak in the optical reflection spectrum of samples filled with ZnO in comparison with the initial opal matrices. The results obtained by these two methods are consistent with each other. Optimum conditions for synthesizing ZnO-filled opals in order to attain the highest intensity of ultraviolet luminescence were determined. It was shown that using “raw” opals, whose voids are incompletely filled with the semiconductor material, leads to a severalfold increase in the intensity of the edge excitonic emission band at room temperature. The results obtained can be used in the development of efficient directed laser light sources in the ultraviolet spectral range based on the “photonic crystal” effect.