Influence of parameters of the semiconductor–dielectric interface on the current of the guard ring of silicon photodiodes

Relationships, which determine requirements for the resistance of the inversion layer for decreasing the influence of the guard ring on the dark current and photodiode noisess and allow obtaining the specified intercoupling coefficient between photosensitive elements in multielement photodiodes, are given. It is shown that dependences of the current of the guard ring on the bias voltage and the charge on the Si–SiO₂ interface in the presence of the inversion layer satisfy the current generation model in the space-charge region of the current. The resistance of the inversion layer increase with an increase in the bias voltage in accordance with the relationship R_u ～ V^1.5.     

To the understanding of the formation of the III–V based droplet epitxial nanorings

The paper deals with the kinetics of the droplet epitaxial GaAs quantum ring formation grown on AlGaAs (0 0 1) surface. The observation is, that the aspect ratio of these nano structures is depends not only on the technological parameters but on the size of the initial droplet. Under appropriate growth conditions, the depressions, in the middle of the rings are deeper than the surface level of the substrate. A large number of tests show, that the depressions in the middle of the small rings are often deeper than that of the larger ones. The number is larger, than just statistical fluctuation. An explanation for this phenomenon and its kinetics are given in the paper, based on the size dependence of the material properties, like for instance solubility. The plausible explanation assumes is that the probability of the crystal seed formation in the larger droplets is higher.     

CVD-growth of CNT with the use of catalutic Ct–Me–N–O thin films incorporated in the technology

The process of the formation of carbon nanotube arrays on Ct–Me–N catalytic alloys of low nickel content (10–20 at %) by chemical vapor deposition, where Ct is a catalytic metal from the group of Ni, Co, Fe, and Pd, and Me is a transition metal of group IV–VII of the periodic table, was investigated. It is shown that CNT grow effectively when the alloy contains Ti, V, Cr, Zr, Hf, Nb, and Ta. The addition of nitrogen and oxygen to the alloy’s composition gives rise to a buildup of oxynitrides, expelling of the catalyst, and formation of its clusters on the surface. The replacement of metals in the alloy has an effect on the diameter of the CNT. Moreover, the alloy films 10–500 nm thick can be used for the CNT growth, which is responsible for high degree of homogeneity and the repeatability of the process. CNT growth was not observed when the alloy contained W and Re.     

Selection of Parameters of the Primary Feed of the Luneberg Lens for the Sum–Difference Operating Mode

Excitation of the Luneberg lens by an arc antenna array of open-ended rectangular waveguides forming the H₁₀ wave is studied. Technical limitations imposed on the array of primary feeds in order to form the sum and difference operating modes of the antenna system are discussed.     

Effect of Nonlinearity of the Phonon Spectrum on the Thermal Conductivity of Nanostructured Materials Based on Bi–Sb–Te

A theoretical investigation of the lattice thermal conductivity of nanostructured materials based on Bi–Sb–Te is presented. The calculations were based on relaxation time approximation and took into account both the real phonon spectra, obtained from first-principles by use of density functional theory, and the anisotropy of phonon relaxation time. Phonon relaxation time data were determined from experimental values of the lattice thermal conductivity. The decrease of the thermal conductivity caused by the nanostructure was compared with results from calculations based on the linear Debye approach. Estimation showed that phonon boundary scattering can lead to a 55% decrease of thermal conductivity for a grain size of ~20 nm in the Debye approximation. Taking the nonlinearity of the acoustic phonon spectrum into account leads to a 20% larger decrease of the thermal conductivity because of boundary scattering. The reason is that consideration of the real phonon spectrum increases the relative contribution to thermal conductivity of acoustic phonons with low frequencies that are scattered more strongly at nanograin boundaries. Similarly, estimation of lattice thermal conductivity reduction as a result of phonon scattering by nanoinclusions gave an 8% larger decrease when the real phonon spectrum was used rather than the linear Debye approximation. For such a substantial decrease of lattice thermal conductivity, the effect of the optical phonons was estimated; it was shown that optical phonons can reduce the change of thermal conductivity as a result of grain boundary scattering by no more than 10%. Finally, the minimum lattice thermal conductivity was estimated to be 0.07 W/m K because of acoustic modes (0.09 W/m K in the Debye approach) and 0.14 W/m K when the contribution of optical modes was also taken into consideration.     

Defects of the structure of semiconductor superlattices grown on the basis of II–VI alloys

The specific features of defects of crystal lattices in multilayer device structures containing small-period (T ? 20 nm) superlattices of type I ZnSe/Cd _x Zn_{1 ? x} Se/ZnSe/.../ZnSe/(001)GaAs and type II ZnS/ZnSe_{1 ? x} S _x /ZnS/.../ZnS/(001)GaAs are studied by the methods of X-ray diffractometry and diffraction rocking pseudocurves, and partially by the X-ray topography. According to the data of quantitative analysis of the X-ray diffraction spectra, the periods of superlattices are in the range T _I = 11.3–16.1 nm (for the compositions Cd _x Zn_{1 ? x} Se with x ₁ = 0.047 and x ₂ = 0.107) for type I superlattices and T _II = 15.6–17.2 nm for type II superlattices (for the compositions ZnSe_{1 ? x} S _x with x ₁ = 0.20 and x ₂ = 0.10). The widths of diffraction peaks from both the ZnSe layers and small-period superlattices in the diffraction rocking pseudocurves considerably exceed their widths in the X-ray diffraction spectra. This fact proves that a pronounced plastic strain with the formation of series of rectilinear dislocations in the crossing slip systems took place in the studied device structures. In order to exclude the generation of dislocations in the growth processes, it is necessary to decrease the concentration of the solid solution to the values x < 0.047 for the first type of superlattices and to the values x ? 0.062 for the second type of superlattices, and to decrease the thickness of the ZnSe and ZnS layers.     

The Influence of the Crystal Structure of the GaSb–InAs Matrix on the Formation of InSb Quantum Dots

Semiconductors - Uniform arrays of the InSb quantum dots with a surface density of nQD = 2 × 109 cm–2 were obtained by liquid phase epitaxy on a matrix layer based on a multicomponent...     

Effect of the chemical composition of Cu–In–Ga–Se layers on the photoconductivity and conversion efficiency of CdS/CIGSe solar cells

The effect of the [Ga]/[In+Ga] ratio of gallium and indium on the microwave photoconductivity of Cu–In–Ga–Se (CIGSe) films and on the efficiency of solar cells fabricated in accordance with the same technology is investigated. According to the observations of a field-emission scanning electron microscopy (FESEM), the grain size decreases with increasing Ga content. With increasing gallium content in the samples, the photogenerated-electron lifetime and the activation energy of the microwave photoconductivity also decrease. The changes in the activation energy of the through conduction in darkness are less than 20%. Analysis of the obtained data shows that the known effect of the gallium gradient on the efficiency should be associated with modification of the internal structure of grains instead of with their boundaries.     

Voltage oscillations in the case of the switching effect in thin layers of Ge–Sb–Te chalcogenides in the current mode

The I–V characteristics obtained for layers of chalcogenide vitreous semiconductor of the Ge–Sb–Te system in the current-generator mode are investigated. The instability region, i.e., the region of conductivity oscillations, observed in the case of the switching effect under conditions of a set current is revealed. The key parameters describing these oscillations and the conditions of their occurrence are investigated in detail. Analysis of the obtained data shows that, to explain the oscillations in the instability region, it is necessary to take into account an increase in the current density and the process of heat exchange between the current filament that arises in the film upon switching and the environment.     

Limiting amplitude–frequency characteristics of the output cavities of klystrons

An analytical ratio determining the maximum possible amplitude of the interaction impedance of the output cavity of the klystron generally connected to N passive cavities forming a filter system is obtained.     

Effect of the anode-emitter injection efficiency on the characteristics of hybrid SIT–MOS transistors

The possibility of optimizing high-voltage hybrid SIT–MOP transistors (HSMTs) by means of a local reduction in lifetime near the anode emitter and/ or by decreasing its injection efficiency by three different methods is studied using two-dimensional numerical simulation. It is shown that all four optimization methods are equivalent from the physical point of view and make it possible to decrease the turn-off energy loss E_off by 30–40%, as in insulated gate bipolar transistors (IGBTs). However, all other conditions being equal, the energy E_off in the HSMT appeared 15–35% lower than in equivalent trench IGBTs.     

Design and Qualification of Pr–Fe–Cu–B Alloys for the Additive Manufacturing of Permanent Magnets

The direct use of an advanced binder-free additive manufacturing technique, namely laser powder bed fusion (L-PBF), does not easily allow obtaining variously shaped, fully dense Nd–Fe–B magnets with high coercivity. The process inherently leads to the re-melting of the powder and appearance/disappearance of undesired/desired microstructural features responsible for low and large coercivity. In this work, the development of a useful microstructure responsible for high coercivity in Pr₂₁Fe_73.5Cu₂B_3.5 and Nd₂₁Fe_73.5Cu₂B_3.5 alloys and a possible way to produce fully dense permanent magnets via additive manufacturing processes is demonstrated using: (i) suction casting technique, which provides a high cooling rate and thus similar microstructures as in L-PBF but requires only very small amounts of powder; (ii) conventional L-PBF processing using kg of powder, and (iii) a subsequent annealing treatment that is similar to a conventional sintering treatment. The subsequent heat treatment is necessary to develop high coercivity by forming a novel microstructure: hard magnetic (Nd,Pr)₂Fe₁₄B grains embedded in a matrix of intermetallic (Nd,Pr)₆Fe₁₃Cu phase. Furthermore, it is demonstrated that Pr₂₁Fe_73.5Cu₂B_3.5 exhibits a higher coercivity than Nd₂₁Fe_73.5Cu₂B_3.5 because of a finer and more homogeneous grain size distribution of the Pr₂Fe₁₄B phase. The final L-PBF printed Pr₂₁Fe_73.5Cu₂B_3.5 samples provide a coercivity of 0.75 T.     

Savitzky–Golay filtering of the spectral sensitivity of photodetector arrays

Recalculation of spectral sensitivity of photodetector arrays with a relatively low signal-to-noise ratio necessitates the analysis of noise filtering with maintaining of the positions of boundaries and maximum sensitivity. Methods for filtering of spectral characteristics of sensitivity (moving average method and its modifications, spline interpolation, calculations using the Bezier curves, and Savitzky–Golay procedure) are compared. Criteria for selection of nondestructive calculation procedure that does not introduce errors in the boundaries of the range and maximum sensitivity of photodetector arrays are determined. An optimal method for recalculation of spectral sensitivities of photodetector arrays is chosen and substantiated.     

Influence of the annealing temperature on the ferroelectric properties of niobium-doped strontium–bismuth tantalate

Characteristics of ferroelectric thin films of niobium-doped strontium–bismuth tantalate (SBTN), which were deposited by magnetron sputtering on Pt/TiO₂/SiO₂/Si substrates, are investigated. To form the ferroelectric structure, deposited films were subjected to subsequent annealing at 700–800°C in an O₂ atmosphere. The results of X-ray diffraction showed that the films immediately after the deposition have an amorphous structure. Annealing at 700–800°C results in the formation of the Aurivillius structure. The dependences of permittivity, residual polarization, and the coercitivity of SBTN films on the modes of subsequent annealing are established. Films with residual polarization 2P_r = 9.2 µC/cm², coercitivity 2E_c = 157 kV/cm, and leakage current 10^–6 A/cm² are obtained at the annealing temperature of 800°C. The dielectric constant and loss tangent at frequency of 1.0 MHz were ε = 152 and tan δ = 0.06. The ferroelectric characteristics allow us to use the SBTN films in the capacitor cell of high density ferroelectric random-access non-volatile memory (FeRAM).     

Experimental study of the effect of parametric noise on the Andronov–Hopf bifurcation in brusselator

Specific features of the Andronov–Hopf bifurcation in the model of brusselator in the presence of parametric noise are numerically and experimentally studied. Regularities of evolution of the probability distribution with an increase in the noise intensity are typical of the additive and multiplicative effect of the Gaussian white noise. The existence of bifurcation interval corresponding to the gradual transition to the generation regime is experimentally revealed for both additive and multiplicative noise.     

Hardware realization of the robust time–frequency distributions

A hardware realization of the L-estimate forms of robust time–frequency distributions is proposed. This hardware realization can be used for instantaneous frequency estimation for signals corrupted by a mixture of impulse and Gaussian noise. The most complex part in the hardware implementation is the block that performs sorting operation. In addition to the continuous realization, a recursive realization of the Bitonic sort network is proposed as well. The recursive approach also provides a fast sorting operation with a significantly reduced number of components. In order to verify the results, the FPGA implementations of the proposed systems were designed.     

Ab initio studies of the band parameters of III–V and II–VI zinc-blende semiconductors

Electronic band-structure calculations are performed for zinc-blende III–V (AlP, AlAs, AlSb, GaP, GaAs, GaP, InP, InAs, and InSb) and II–VI (ZnS, ZnSe, ZnTe, CdS, CdSe, and CdTe) semiconductors using an ab initio pseudopotential method within a local-density approximation (LDA). Lattice parameters, band gaps, Luttinger parameters, momentum matrix elements and effective masses are studied in detail. It is shown that LDA calculations cannot systematically give accurate band parameters. It is found that LDA band parameters calculated using experimentally determined lattice constants are more accurate than those using LDA lattice constants. We found that inclusion of the d electrons of Group-II atoms in the core gives more accurate band parameters.     

Analysis of the Temperature Dependence of the Capacitance–Voltage and Conductance–Voltage Characteristics of Au/TiO2(rutile)/n-Si Structures

The capacitance–voltage–temperature (C–V–T) and the conductance/angular frequency–voltage–temperature (G/ω–V–T) characteristics of Au/TiO₂(rutile)/n-Si Schottky barrier diodes (SBDs) were investigated over the temperature range from 200 K to 380 K by considering the series resistance effect. Titanium dioxide (TiO₂) was deposited on n-type silicon (Si) substrate using a direct-current (DC) magnetron sputtering system at 200°C. To improve the crystal quality, the deposited film was annealed at 900°C to promote a phase transition from the amorphous to rutile phase. The C ^?2 versus V plots gave a straight line in the reverse-bias region. The main electrical parameters, such as the doping concentration (N _D), Fermi energy level (E _F), depletion layer width (W _D), barrier height (ф _CV), and series resistance (R _S), of Au/TiO₂(rutile)/n-Si SBDs were calculated from the C–V–T and the G/ω–V–T characteristics. The obtained results show that ф _CV, R _S, and W _D values decrease, while E _F and N _D values increase, with increasing temperature.