Vol 53, No 4 (2019)

The change in the recombination properties of individual dislocations and dislocation trails in silicon due to the diffusion of nickel and copper during chemical-mechanical polishing at room temperature is studied by the electron-beam- and light-beam-induced current techniques. It is found that the introduction of nickel results in an increase in the recombination activity of both dislocations and dislocation trails. The introduction of copper does not induce any substantial change in the contrast of extended defects.

The full set of thermoelectric parameters of heavily doped p-PbTe in the temperature range of 300–1200 K at an acceptor doping level of N_a = 1 × 10¹⁹–4 × 10²⁰ cm^–3 and a heavy-hole band depth ranging from 0.36 to 0.7 eV is calculated. The figure-of-merit value Z is found to be highly sensitive to the doping level and increased by a factor of 1.5 with an increase in the dopant concentration from 1 × 10¹⁹ to 5 × 10¹⁹ cm^–3; the maximum Z value is found to correspond to N_a = (1–2) × 10²⁰ cm^–3. It is demonstrated that the change in the heavy-hole band depth leads to a noticeable shift of the Z maximum position along the temperature axis without noticeable Z maximum variation. The temperature corresponding to the maximum Z value is similar to that at which the top of the light-hole band crosses the Fermi level. The maximum calculateded ZT value is shown to be 1.64. At a heavy-hole band depth of 0.5 eV, the calculated results agree well with the available experimental data.

Expressions for the Auger- and radiative-recombination rates are derived in terms of Kane’s model for materials with a band-gap width close to the spin-orbit splitting energy, which is the case for InAs, InAsSb solid solutions, etc. Our results are compared with simplified expressions for recombination rates, frequently used in publications. It is shown that the nonparabolicity of the electronic structure should be taken into account in calculations of the recombination rates. As an example, the temperature dependences of the charge-carrier lifetimes governed by radiative and non-radiative processes are calculated for InAsSb solid solutions.

The transformation of micropits on large terraces of the Si(111) surface containing no vicinal atomic steps has been investigated by in situ ultrahigh-vacuum reflection electron microscopy upon thermal annealing of the substrate in the range of 1200–1400°C. A procedure for the formation of micropits on large terraces of the Si(111) surface with the application of focused-ion-beam (Ga⁺) technology has been proposed. It has been found that the micropit decay kinetics varies upon reaching the critical radius R_crit, which is caused by the activation of nucleation of two-dimensional vacancy islands on the micropit bottom. A theoretical model describing variations in the lateral sizes of the micropit both before and after reaching R_crit has been proposed. Based on analysis of the found temperature dependence of the nucleation frequencies of two-dimensional vacancy pits on the micropit bottom, the effective energy of nucleation of a vacancy island has been determined to be 4.1 ± 0.1 eV.

A three-dimensional Monte Carlo simulation algorithm is used to study the contrast of two dislocations perpendicular to the irradiated surface of an n-doped silicon sample in the electron beam induced current mode. The dislocations are positioned in the irradiation trajectory, and each of both is considered as a cylinder where the minority carrier diffusion length varies abruptly from a low inside dislocations up to a high value outside dislocations. The EBIC contrast was obtained by simulating the random diffusion of carriers generated at point-like sources randomly distributed within the generation volume. Results are analyzed on the basis of change in the generation volume in the bulk of the sample and of carrier trapping process inside dislocations. The EBIC contrast increases with the increase of the electron beam energy. It also increases when the minority diffusion length inside dislocations, or their separating distance decreases.

The influence of the substrate material on the properties of gallium-oxide films formed on sapphire and n(p)-GaAs semiconductor wafers by high-frequency magnetron-assisted deposition is studied. The films grown on insulating substrates, as a rule, are of the n type and possess a high resistance. The increase in their conductivity with temperature is defined by the ionization of deep donor centers, whose energy is (0.98 ± 0.02) eV below the bottom of the conduction band. Gallium-oxide films grown on single-crystal GaAs layers are of the n type as well, irrespective of the conductivity type of the semiconductor substrates. However, the conductance of such films is noticeably higher, which is attributed to the possible diffusion of uncontrollable impurities from the semiconductor into the growing gallium-oxide layer. The electrical characteristics of Ga₂O₃– semiconductor structures are defined to a larger extent by the properties of the oxide–semiconductor interface than by the properties of the contacting materials. In the reverse branch of the current–voltage characteristics of Ga₂O₃/p-GaAs samples before annealing, a region of N-type negative resistance is observed. After annealing of the gallium-oxide films at 900°C (30 min), the conductance of the structures corresponds to the current–voltage characteristic of a backward diode.

Results of studying the features of the current–voltage (I–V) and capacitance–voltage characteristics of field-resistant silicon–ultrathin oxide–polysilicon structures are presented. It turns out that the total recharging of localized electron states and minority carriers concentrated near the substrate–insulator interface, which occurs with a variation in the field voltage, is an order of magnitude higher than that of samples susceptible to damage by the field stress effect. The tunneling I–V characteristic is significantly asymmetric; notably, the current flowing from the field electrode into the silicon substrate is several orders of magnitude lower when compared with the current flowing from silicon to polysilicon at identical external voltages dropping across the insulating layer. To explain this asymmetry, it is assumed that a potential barrier in the transition layer from polysilicon to oxide, which separates the semiconductor electrode and substrate, has a height of ~1 eV and therefore always hinders electrical transport; for reverse currents, this barrier stops limiting the conductivity as soon as the tunneling level becomes higher than it.

Electric-field nonuniformity in the active region of a LED (light-emitting diode) heterostructure based on five identical GaN/InGaN quantum wells is investigated by the electroreflectance method. The energies of band-to-band transitions in the quantum wells and barriers are determined from the analysis of electroreflectance spectra using the Kramers–Kronig transforms. The procedure for estimating the electric-field strength in separate quantum wells of the active region by the position of spectral lines is proposed. It is found that the energies of the main transition in quantum wells of the active region with zero bias of the p–n junction differ by a magnitude on the order of 140 meV, which corresponds to a difference in the electric-field strengths of 0.78 MV/cm. It is shown that the nonuniformity of the electric field in the active region depends on the p–n junction bias.

Herein, we have measured the mobility of Hole’s for the configuration FTO/TiO₂/CH₃NH₃PbBr₃/PEDOT:PSS/Al by the SCLC regime. The current–voltage (I–V) characteristics of the CH₃NH₃PbBr₃ perovskite based device shows the rectifying behavior as Schottky diode. Different parameters of the proposed device such as saturation current, ideality factor, barrier height have been taken out from I–V characteristics. The highest Hole’s mobility from TiO₂ thin film through the perovskite and PEDOT:PSS film to the top aluminum electrode has of order 1.59 × 10^–4 cm² V^–1 s^–1. Moreover, the proposed device shows the TFSCLC regime at lower voltage while, at higher voltages it shows the TCLC regime. In addition to this, some important parameters like junction resistance, capacitance and carrier lifetime of device can be measured by the spectroscopy analysis of impedance.

The Raman spectra of SiO₂ films containing InSb spherical nanocrystals produced by ion-beam synthesis are studied. TO- and LO-like modes in the spectra of the InSb nanocrystals are detected at frequencies of 187 and 195 cm^–1, respectively. The shift of these modes to high frequencies with respect to the corresponding frequencies in InSb bulk crystals is analyzed from the viewpoint of the influence of the quantum-confinement effect, strains in nanocrystals, the surface phonon frequency, and scattering at the frequency corresponding to stretched anion–cation modes at the surface of polar spherical nanocrystals. The position of the 195-cm^–1 mode corresponds to LO phonons in InSb nanocrystals hydrostatically compressed in the SiO₂ matrix at pressures of about 10 kbar. The 187-cm^–1 mode corresponds to resonance at the Fröhlich frequency.

The effect of a substrate misorientation degree from a singular face on the composition and morphology of layers of InAs_xSb_{1 –x} solid solutions obtained by molecular-beam epitaxy on a GaAs surface has been investigated. The substrates of GaAs wafers with the orientation (100) misoriented in the direction [110] by 0°, 1°, 2°, and 5° are used. The heterostructures are grown at temperatures of 310°C and 380°C (respectively, the lower and upper boundaries of the temperature range in which structurally perfect InAs_xSb_{1 –x} films form). The effect of the molecular form of arsenic (As₂ or As₄) on the composition of the layers is studied. The composition and structural properties are investigated using high-resolution X-ray diffractometry (HRXRD) and atomic-force microscopy (AFM). It is established that, in the series of misorientation angles 0° → 5°, the arsenic fraction x increases consecutively when using fluxes of both As₂ and As₄ molecules. With the As₂ molecular flux, the fraction x increases only a little (1.05 times) with increasing degree of misorientation, while, when using the As₄ flux, the increase in x is 1.75 times. An increase in the growth temperature leads to growth in the arsenic fraction in the solid solution. The surface morphology improves with an increasing degree of misorientation at a low growth temperature and degrades at a high temperature.

The problem of the formation and propagation of a large-amplitude shock electromagnetic wave in a strip transmission line (TL) based on a distributed semiconductor diode is analytically solved. The solution correctly considers its nonlinearity, dissipation, and time dispersion. The results of the theory are used to estimate the parameters of the TL as a sharpener of the pulse front voltage applied to the line input.

For the first time, a self-consistent computational–theoretical description of the physical processes in reversely switched dynistors (RSDs) is obtained when operating in pulse-frequency modes with a limited heat sink. A simplified representation of the nonlinear multiscale mechanism of interaction between the injection and heat-transfer subsystems is substantiated, and a method for calculating the maximum frequency of the RSD switching unit is developed on this basis. The dependence of the permissible frequency on the cooler power is calculated for the set parameters of the chip and the shape of the switched pulses. It is shown that, with a proper heat sink, each from all RSD modules with a chip area of 1 cm² and an operating voltage of U ≈ 2.5 kV are able to switch an energy of 0.25 J per pulse with a repetition frequency of up to 30 kHz. For high-voltage generators on their basis with U ≈ 100 kV, the power transmitted to a load at this frequency amounts to several fractions of a MW.

We present the results of a comparative study on behaviour of the photovoltaic parameters in perovskite (PSC), dye-sensitized (DSC) and crystalline silicon (c-Si) solar cells under various intensities of solar radiation (10–1000 W/m²). It was found that unlike c-Si, the power conversion efficiencies of PSC and DSC under low radiation intensities are comparable with the corresponding values observed under standard light intensity of 1000 W/m² (AM1.5G). We have shown that high performance of the PSC and DSC at low and diffuse lighting conditions can be explained by the properties of the nanostructured TiO₂-based photoelectrodes depending on the structure, morphology and the thickness of the TiO₂ layers.

The optical and electrical characteristics of films consisting of nanocrystalline silicon (nc-Si) deposited onto substrates by the high-voltage electrospraying of nc-Si sols in ethanol are investigated. It is found that the interaction of ethanol droplets carrying Si nanoparticles with a corona-discharge electric field leads to the polymerization of ethanol and the formation of a polymer layer on the Si-nanoparticle surface. A high-voltage facility for depositing the films using an additional focusing electrode allows one to change the geometry of the electric field and intensity in the region of the ethanol droplet flow. As a result, nc-Si films with qualitatively different properties of the polymer on the nanoparticle surface are formed, specifically, nc-Si_A and nc-Si_B, obtained without a focusing electrode and with it, respectively. Upon annealing at temperatures of up to 400°С, the optical band gap E_g of the nc-Si_A films increases from ~1.9 to ~2.2 eV, while the E_g value of the nc-Si_B films remains constant and amounts to 1.85 eV. The constant E_g value of the nc-Si_B films is explained by the properties of the polymer on the Si-nanoparticle surface and the more effective blocking of oxygen penetration from the surrounding environment upon annealing at temperatures of up to 400°C than in the case of a polymer in nc-Si_A films. The temperature dependences of the dark and photoinduced conductivity of nc-Si_A films are approximated with good accuracy by two activation-type exponential functions and the dark activation energies are ~0.75 and 0.1 eV, respectively. The conductivity of the nc-Si_A films noticeably decreases under irradiation of the samples at wavelengths of 460–470 nm. The temperature dependences of the conductivity of the nc-Si_B films are approximated with good accuracy by exponential functions with activation energies of 0.73 (in the dark) and 0.59 eV (under photoexcitation). In contrast to the case of nc-Si_A films, the photoconductivity of nc-Si_B films grows more than fourfold relative to the dark conductivity under analogous illumination. The nc-Si_B films are photoactive and sandwich-like Al/nc-Si_B/Al structures can generate a voltage. The dark conductivity and photoconductivity of the nc-Si_A films in the voltage range of V > 2 V are determined by the two-center Poole–Frenkel effect; the concentration of the centers affecting the Poole–Frenkel conductivity is ~3 × 10¹⁷ cm^–3. In nc-Si_B films in the voltage range of 2–5 V, electron transport is determined by space-charge-limited currents and, at high voltages, by the two-center Poole–Frenkel effect. The concentration of traps contributing to the space-charge-limited currents is ~4 × 10¹⁶ cm^–3. The concentration of Poole–Frenkel centers affecting the conductivity decreases according to the activation law with an activation energy of 0.7 eV from 3 × 10¹⁶ to 2 × 10¹⁴ cm^–3 with a decrease in temperature from 120°C to 40°C.

Zinc Aluminum Oxide thin films were deposited on glass substrates by reactive DC magnetron sputtering method by varying oxygen flow rates from 1 to 4 sccm. Glancing angle X-ray diffraction patterns ofzinc aluminum oxide thin films exhibits (0 0 2) peak with c-plane preferentially oriented parallel to the substrate. The surface morphology and elemental analysis of the films was observed by field emission scanning electron microscopy attached with energy dispersive X-ray analysis spectroscopy. An average optical transmittance of 83–90% is obtained for the films deposited at various oxygen flow rates. The optical band gap of the films increases from 3.41 to 3.53 eV with the increase of oxygen flow rate due to Burstein–Moss effect. The optical dispersion parameters such as dispersion energy (E_d), oscillator energy (E_o) and static refractive index (n_o) were determined using the Wemple-DiDomenico (W-D) single oscillator model. The nonlinear optical parameters such as optical susceptibility (χ⁽¹⁾), third order nonlinear optical susceptibility (χ⁽³⁾) and nonlinear refractive index (n₂) were also determined.