Vol 50, No 8 (2016)

The depth distributions of structural damage induced in Si at room temperature by the implantation of P and PF₄ with energies from 0.6 to 3.2 keV/amu are experimentally studied in a wide range of doses. It is found that, in all cases, the implantation of molecular PF₄ ions forms practically single-mode defect distributions, with maximum at the target surface. This effect is caused by an increase in the generation of primary defects at the surface of the target. Individual cascades formed by atoms comprising molecule effectively overlap in the surface vicinity; this overlap gives rise to nonlinear processes in combined cascades due to a high density of displacements in such cascades. Quantitative estimation of increase of effectiveness of point defect generation by PF₄ ions in respect to P ions is done on the base of experimental data.

The temperature dependences of the Fermi level, concentrations of charge carriers, and their effective mass ratio in the Bi_1–xSb_x system (x = 0.06, 0.12) are determined on the basis of quantitative analysis of the temperature dependence of the Hall coefficient in the temperature range of 77–300 K.

The band of intrinsic (e–h) radiation emission by the subsurface potential barriers of crystal grains and the edge doublet band arising as LO-phonon replicas of the e–h band are observed in the spectra of the low-temperature (4.2 K) photoluminescence of fine-grained (with a grain size of d_cr ≤ 1 µm) CdTe films. Film doping with the In impurity results in quenching of the doublet band, while heat treatment leads to activation of the intrinsic band, a short-wavelength shift of the red boundary (ΔE_r = 16–29 meV) and the halfwidth modulation (Δ_A = 6–17 meV) of which correlate with the height of micropotential barriers and the temperature of recombining hot photocarriers.

The optical absorption coefficient α in p⁺-InSb layers (with hole concentrations of p ≈ 1 × 10¹⁷–1.2 × 10¹⁹ cm^–3), grown by liquid-phase epitaxy on p-InSb substrates, is measured in the spectral range of 5-12 µm at 90 K, and the impurity photoconductivity is measured (at 60 and 90 K) in p⁺–p structures. It is found that a in the p⁺ layers reaches a value of 7000 cm^–1 (at p ≈ 2 × 10¹⁹ cm^–1). It is shown that the measured substrate value of (α ≈1–3 cm^–1) is overestimated in comparison with estimates (α ≈ 0.1 cm^–1) based on comparing the photoconductivity data. This discrepancy is explained by the fact that the optical transitions of holes responsible for photoconductivity are obscured by the excitation of electrons to the conduction band. The photoionization cross section for these transitions does not exceed 1 × 10^–15 cm².

The effect of the annealing of titanium oxide films on the electrical properties of metal–TiO₂–n-Si structures is investigated. It is shown that, regardless of the annealing temperature, the conductivity of the structures at positive gate potentials is determined by the space-charge-limited current in the insulator with traps exponentially distributed in terms of energy. At negative gate potentials, the main contribution to the current is provided by the generation of electron–hole pairs in the space-charge region in silicon. The properties of the TiO₂/n-Si interface depend on the structure and phase state of the oxide film, which are determined by the annealing temperature.

The negative-U impurity stripes confining the edge channels of semiconductor quantum wells are shown to allow the effective cooling inside in the process of the spin-dependent transport. The aforesaid also promotes the creation of composite bosons and fermions by the capture of single magnetic flux quanta at the edge channels under the conditions of low sheet density of carriers, thus opening new opportunities for the registration of quantum kinetic phenomena in weak magnetic fields at high temperatures up to the room temperature. As a certain version noted above, we present the first findings of the high temperature de Haas–van Alphen (300 K) and quantum Hall (77 K) effects in the silicon sandwich structure that represents the ultranarrow, 2 nm, p-type quantum well (Si-QW) confined by the delta barriers heavily doped with boron on the n-type Si (100) surface. These data appear to result from the low density of single holes that are of small effective mass in the edge channels of p-type Si-QW because of the impurity confinement by the stripes consisting of the negative-U dipole boron centers which seems to give rise to the efficiency reduction of the electron–electron interaction.

The carrier recombination dynamics in an ensemble of GaN/AlN quantum dots is studied. The model proposed for describing this dynamics takes into account the transition of carriers between quantum dots and defects in a matrix. Comparison of the experimental and calculated photoluminescence decay curves shows that the interaction between quantum dots and defects slows down photoluminescence decay in the ensemble of GaN/AlN quantum dots.

The nonequilibrium state of a two-dimensional electron gas in the quantum-Hall-effect regime is studied in Hall bars equipped with additional inner contacts situated within the bar. The magnetic-field dependence of the voltage drop between different contact pairs are studied at various temperatures. It was found that the voltage between the inner and outer contacts exhibits peaks of significant amplitude in narrow magnetic-field intervals near integer filling factors. Furthermore, the magnetic-field dependence of the voltage in these intervals exhibits a hysteresis, whereas the voltage between the outer contacts remains zero in the entire magnetic-field range. The appearance of the observed voltage peaks and their hysteretic behavior can be explained by an imbalance between the chemical potentials of edge and bulk states, resulting from nonequilibrium charge redistribution between the edge and bulk states when the magnetic field sweeps under conditions of the quantum Hall effect. The results of the study significantly complement the conventional picture of the quantum Hall effect, explicitly indicating the existence of a significant imbalance at the edge of the two-dimensional electron gas: the experimentally observed difference between the electrochemical potentials of the edge and bulk exceeds the distance between Landau levels by tens of times.

The effect of uniaxial deformation under a stress of up to 6 kg/cm² on the current–voltage characteristics of a p-Ge/n-GaAs heterostructure is studied at 300 and 77 K. It is found that both the forward and reverse currents increase with increasing pressure, with the change in the forward current exceeding that in the reverse current by an order of magnitude. Deformation is also examined in relation to different crystallographic directions. It is found that the effect is at a maximum if the compression direction is parallel to <111>. This result can be used in the development of uniaxial-strain sensors.

One of the most important drawbacks which caused the silicon based technologies to their technical limitations is the instability of their products at nano-level. On the other side, carbon based materials such as carbon nanotube (CNT) as alternative materials have been involved in scientific efforts. Some of the important advantages of CNTs over silicon components are high mechanical strength, high sensing capability and large surface-to-volume ratio. In this article, the model of CNT Schottky transistor current which is under exterior applied voltage is employed. This model shows that its current has a weak dependence on thermal velocity corresponding to the small applied voltage. The conditions are quite different for high bias voltages which are independent of temperature. Our results indicate that the current is increased by Fermi velocity, but the I–V curves will not have considerable changes with the variations in number of carriers. It means that the current doesn’t increase sharply by voltage variations over different number of carriers.

Structures of films produced from a water-based graphene oxide ink by 2D printing on various substrates, including those of the flexible type, are compared. It was shown that the deposition of a thin polyvinyl alcohol film making substrates hydrophilic leads not only to more uniform application of the ink, but also to a denser film structure with a shallower surface profile. The processing of a graphene-oxide suspension in a blender additionally reduces the particle size of the suspension, which results in improvement of the structure and, on the whole, a shallower surface profile of the film. Comparison of the electrical properties of films on silicon with various coatings hydrophilizing the substrates demonstrated that the properties of the structures strongly depend on the type of coatings, which can change the conductivity type of the silicon substrate and lead to doping of the graphene-oxide film. At graphene-oxide film thicknesses not exceeding 25 nm, noticeable currents (>1 µA) appear in the films at voltages higher than 1–1.5V. The graphene-oxide layers are promising for the fabrication of protective and insulating coatings and sensors and, in the case of reduction, for the deposition of transparent electrodes.

The photoinduced degradation of photovoltaic converters based on an a-Si:H/µc-Si:H tandem structure under a standard illuminance of 1000 W/m² is studied. The spectral and current–voltage characteristics of specially fabricated samples with various degrees of crystallinity of the intrinsic layer in the lower (microcrystalline) cascade are measured in the course of the tests.

In order to raise the efficiency of solar cells and reduce the cost of their production, a new process for obtaining silicon ingots based on the so-called moonlike technology is developed. New technologies, which use “solar-grade” silicon, make it possible to fabricate solar cells at a lower cost with a higher efficiency of solar-energy conversion. It is exactly for this reason that the “monolike” process was tested and optimized by us for Kazakhstan solar-grade silicon. The aim of this study is a comparison of the characteristics of solar cells fabricated from “monolike” silicon with those of solar cells obtained on the basis of multicrystalline silicon grown by oriented crystallization. For our study, ingots of multicrystalline silicon are grown on an industrial scale and through the use of Kazakhstan-sourced silicon; solar cells are fabricated and the characteristics of the obtained silicon ingots and solar cells are studied.

We report the fabrication and optical and electrical characterization of photodetectors for the UV spectral range based on single p–n junction nanowires with a transparent contact of a new type. The contact is based on CVD-grown (chemical-vapor deposition) graphene. The active region of the nitride nanowires contains a set of 30 radial In_0.18Ga_0.82N/GaN quantum wells. The structure is grown by metal-organic vaporphase epitaxy. The photodetectors are fabricated using electron-beam lithography. The current–voltage characteristics exhibit a rectifying behavior. The spectral sensitivity of the photodetector is recorded starting from 3 eV and extending far in the UV range. The maximal photoresponse is observed at a wavelength of 367 nm (sensitivity 1.9 mA/W). The response switching time of the photodetector is less than 0.1 s.

We investigate the efficiency of the introduction of a porous layer into the substrate of a silicon-onsapphire structure by the implantation of He ions to enhance the radiation resistance of devices. The properties of the introduced layer and its parameters affecting the concentration of minority charge carriers generated by irradiation are analyzed. The reported results of the analysis and calculations can be used to optimize He-ion implantation conditions during the formation of a porous layer.

The fabrication of a two-layer Si₃N₄/SiO₂ dielectric mask and features of its application in the technology of non-fired epitaxially grown ohmic contacts for high-power HEMTs on AlGaN/GaN heterostructures are described. The proposed Si₃N₄/SiO₂ mask allows the selective epitaxial growth of heavily doped ohmic contacts by nitride molecular-beam epitaxy and the fabrication of non-fired ohmic contacts with a resistance of 0.15–0.2 Ω mm and a smooth surface and edge morphology.

The conductivity of epitaxial n- and p-PbSe thin films after dry etching in radio-frequency highdensity low-pressure inductively coupled argon plasma at a bombarding-ion energy of 200 eV is studied. It is shown that the observed changes in the conductivity can be adequately interpreted in the context of the classical model of the generation of donor-type radiation defects and that the processes of post-irradiation vacuum annealing result in the removal of such defects. The mean free path of charge carriers in p-PbSe films is determined within the context of the Fuchs–Sondheimer theory. It is found that, at room temperature, this parameter is 16 and 32 nm for the specularity parameter 0 and 0.5, respectively.