卷 50, 编号 3 (2016)

In the context of density functional theory, the phonon density of states and phonon dispersion are calculated for ZnGa₂Se₄. The temperature dependence of the heat capacity of ZnGa₂Se₄ in the temperature range 5–400 K is obtained. The calculated frequencies and symmetries of phonon modes in the center of the Brillouin zone are in good agreement with experimental data obtained by Raman spectroscopy and infrared spectroscopy.

All published results of measurements (at 300 K) of the impact ionization coefficients for electrons α_n and holes α_p in 4H–SiC are analyzed. It is shown that the most plausible approximations of dependences of α_{n, p} on electric-field strength E have the usual form α_{n, p} = a_{n, p} exp(–E_{n, p}/E) at fitting-parameter values of a_n = 38.6 × 106 cm^–1, E_n = 25.6 MV/cm, a_p = 5.31 × 106 cm^–1, and E_p = 13.1 MV/cm. These dependences α_{n, p}(E) are used to calculate the highest field strength E_b and thickness w_b of the space-charge region at the breakdown voltage U_b. A number of new formulas for calculating α_{n, p}(E) are obtained from the results of measuring the avalanche-multiplication coefficients and the excess-noise factors under the single-sided illumination of photodiodes with stepped doping.

A quasi-classical method for calculating the narrowing of the Hubbard gap between the A⁰ and A⁺ acceptor bands in a hole semiconductor or the D⁰ and D^– donor bands in an electron semiconductor is suggested. This narrowing gives rise to the phenomenon of a semiconductor transition from the insulator to metal state with an increase in doping level. The major (doping) impurity can be in one of three charge states (–1, 0, or +1), while the compensating impurity can be in states (+1) or (–1). The impurity distribution over the crystal is assumed to be random and the width of Hubbard bands (levels), to be much smaller than the gap between them. It is shown that narrowing of the Hubbard gap is due to the formation of electrically neutral acceptor (donor) states of the quasicontinuous band of allowed energies for holes (electrons) from excited states. This quasicontinuous band merges with the top of the valence band (v band) for acceptors or with the bottom of the conduction band (c band) for donors. In other words, the top of the v band for a p-type semiconductor or the bottom of the c band for an n-type semiconductor is shifted into the band gap. The value of this shift is determined by the maximum radius of the Bohr orbit of the excited state of an electrically neutral major impurity atom, which is no larger than half the average distance between nearest impurity atoms. As a result of the increasing dopant concentration, the both Hubbard energy levels become shallower and the gap between them narrows. Analytical formulas are derived to describe the thermally activated hopping transition of holes (electrons) between Hubbard bands. The calculated gap narrowing with increasing doping level, which manifests itself in a reduction in the activation energy ε₂ is consistent with available experimental data for lightly compensated p-Si crystals doped with boron and n-Ge crystals doped with antimony.

The methods of admittance, I–V, and C–V characteristics are used to investigate In_2xGa_2(1–x)Te₃/InAs and In₂Te₃/InAs heterostructures obtained by the technologies of quasi-closed volume and deposition. The spectrum of the distribution of local energy levels at the interface is established. A new acceptor center with an energy of 0.36 eV alongside the known donor level with an energy of 0.5 eV is found by the method of admittance. The acceptor-center concentration N_t depends on the method of fabrication and technological modes. The kinetics of generation–recombination processes in the temperature range of 70–400 K does not affect the insulating properties of the In₂Te₃ or In_2xGa_2(1–x)Te₃ (x ≈ 0.65) dielectric layer; therefore, the possibility of their use as heterostructures for field-effect transistors is demonstrated.

The method of electrochemical capacitance–voltage profiling is used to study boron-implanted silicon structures for CCD matrices with backside illumination. A series of specially prepared structures with different energies and doses of ion implantation and also with various materials used for the coating layers (aluminum, silicon oxide, and their combinations) is studied. The profiles of the depth distribution of majority charge carriers of the studied structures are obtained experimentally. Also, using the Poisson equation and the Fredholm equation of the first kind, the distributions of the charge-carrier concentration and of the electric field in the structures are calculated. On the basis of the analysis and comparison of theoretical and experimental concentration profiles, recommendations concerning optimization of the structures’ parameters in order to increase the value of the pulling field and decrease the effect of the surface potential on the transport of charge carriers are suggested.

The conditions for fabricating photosensitive TiN/p-InSe heterojunctions by the reactive-magnetron sputtering of thin titanium-nitride films onto freshly cleaved p-InSe single-crystal substrates is investigated. The presence of a tunnel-transparent high-resistivity In₂Se₃ layer at the heterojunction is revealed from analysis of the I–V characteristics, and the effect of this layer on the electrical properties and photosensitivity spectra of the heterostructures is analyzed. The dominant current transport mechanisms through the TiN/p-InSe energy barrier under forward and reverse bias are determined.

The technology of the growth of Si, Ge, and Si_1–xGe_x layers by molecular-beam epitaxy with the use of a sublimation source of monoisotopic ³⁰Si or ²⁸Si and/or gas sources of monogermane ⁷⁴GeH₄ is demonstrated. All of the epitaxial layers are of high crystal quality. The secondary-ion mass spectroscopy data and Raman data suggest the high isotopic purity and structural perfection of the ³⁰Si, ²⁸Si, ⁷⁴Ge, and ³⁰Si_1–x⁷⁴Ge_x layers. The ³⁰Si layers doped with Er exhibit an efficient photoluminescence signal.

The possibility of fabricating highly hydrophobic nanostructured zinc-oxide layers by the inexpensive method of pulsed electrodeposition from aqueous solutions without water-repellent coatings, adapted for large-scale production, is shown. The conditions of the deposition of highly hydrophobic nanostructured zinc-oxide layers exhibiting the “rose-petal” effect with specific morphology, optical properties, crystal structure and texture are determined. The grown ZnO nanostructures are promising for micro- and nanoelectronics as an adaptive material able to reversibly transform to the hydrophilic state upon exposure to ultraviolet radiation.

The influence of the surface layer on the process of the electrochemical deposition of metals and semiconductors into porous silicon is studied. It is shown that the surface layer differs in structure and electrical characteristics from the host porous silicon bulk. It is established that a decrease in the conductivity of silicon crystallites that form the surface layer of porous silicon has a positive effect on the process of the filling of porous silicon with metals and semiconductors. This is demonstrated by the example of nickel and zinc oxide. The effect can be used for the formation of nanocomposite materials on the basis of porous silicon and nanostructures with a high aspect ratio.

A model of the density of states of single-sheet graphene is proposed. The model applies to both the energy region close to the Dirac point and the peripheral region. In the context of the model, the problem of adsorption is solved within an approximation that allows an analytical representation of the band contributions n_b to the occupation numbers of an adatom n_a. The amorphization-induced changes in the occupation numbers of alkali metal and halogen adatoms are estimated.

In this paper, an AlN/GaN-based MOSHEMT is proposed, in accordance to this, a charge control model has been developed analytically and simulated with MATLAB to predict the characteristics of threshold voltage, drain currents and transconductance. The physics based models for 2DEG density, threshold voltage and quantum capacitance in the channel has been put forward. By using these developed models, the drain current for both linear and saturation models is derived. The predicted threshold voltage with the variation of barrier thickness has been plotted. A positive threshold voltage can be obtained by decreasing the barrier thickness which builds up the foundation for enhancement mode MOSHEMT devices. The predicted I_d–V_gs, I_d–V_ds and transconductance characteristics show an excellent agreement with the experimental results and hence validate the model.

High-power thyristor switching from the blocking to conducting state via an overvoltage pulse with nanosecond rise time is studied. Low-frequency tablet thyristors with an operating voltage of 2 kV are used in the experiments. An external pulse providing a voltage rise rate from 0.5 to 6 kV/ns was applied to the thyristors main electrodes. Under these conditions, the time of thyristor switching to the conducting state is 200–400 ps. Empirical relations between the main switching characteristics, i.e., the turn-on voltage, pulse rise time before switching, and time of thyristor switching to the conducting state, are obtained. Numerical simulation shows that the ionization of deep technological defects should be taken into account to explain the results obtained.

The effect of the type of substrate, sapphire substrate (c- and r-orientation) or GaN/Al₂O₃ template (c- and r-orientations), on the nitridation of an amorphous titanium nanolayer is shown. The effect of the titanium-nanolayer thickness on thick GaN epitaxial layer self-separation from the substrate is revealed. The titanium-nanolayer thickness at which thick GaN layer is reproducibly self-separated is within 20–40 nm.

Composite Si–Au layers prepared by laser electrodispersion with different Si:Au ratios are studied. The microscopic structure of the layers is established and their Raman spectra and optical transmission and reflectance spectra are investigated. It is demonstrated that the sputtering of a two-component Si–Au target radically changes the layer morphology. With increasing Au content in the target, the layers become inhomogeneous and a large number of inclusions arise, which contain silicon nanocrystals and a certain amount of gold. Upon the sputtering of a two-component target, inclusions are most likely formed from large molten droplets, which are ejected from the target and do not manage to divide into nanoparticles. The nanocrystalline structure of the inclusions is attributed to the slow inhomogeneous cooling of particles on the substrate. It is concluded that variations in the photosensitivity spectra of heterostructures with the investigated layers are caused by the formation of inclusions containing silicon nanocrystals with the addition of gold.