Photoelectric properties of surface-barrier structures based on Zn<Subscript>2−2<Emphasis Type="Italic">x</Emphasis></Subscript>Cu<Subscript>x</Subscript>In<Subscript>x</Subscript>Se<Subscript>2</Subscript> films obtained by selenization

p-Zn_2?2xCu_xIn_xSe₂ (ZCIS) polycrystalline films 1–2 ¼m thick have been obtained by selenization. Photosensitive surface-barrier In/p-ZCIS structures are fabricated based on the films. The spectra of relative quantum efficiency of the structures obtained by selenization of the initial ZnSe/(Cu-In) and (Zn-Cu-In) films are examined. The optical band gap of the Zn_2?2xCu_xIn_xSe₂ films is determined. Conclusions are reached on the prospects for the use of the obtained films as broadband photoconverters of natural optical radiation.     

Effect of annealing temperature and rate of sputtering on the magnetic properties and microstructure of the polycrystalline nickel films with (200) texture

The dependences of the magnetic properties and morphology of polycrystalline nickel (Ni) films with the (200) texture that are fabricated using the dc magnetron sputtering on the SiO₂/Si(100) substrates on sputtering rate annealing temperature T, and film thickness d are analyzed. It is demonstrated that an increase in the sputtering rate from 17 to 35 nm/min does not affect the saturation magnetization 4πM and ferromagnetic resonance line width ΔH but leads to a significant increase in the coercivity H _c for the films whose thickness d is greater than critical thickness d _cr (d > d _cr). It is also demonstrated that d _cr depends on both sputtering rate and annealing temperature. The films with the thickness d > d _cr exhibit the stripe domain structure whose period increases with increasing d and rate v. The annealing of the films with d ≥ 40 nm at T ≈ 200–400°C results in an increase in ΔH and H _c by a factor of 2–4, an increase in 4πM by 25%, an increase in grain size ξ by a factor of 20–30, and the formation of the stripe domain structure in the films that do not exhibit such structure prior to annealing and substantial strengthening of the (200) texture.     

Method for optimizing the parameters of heterojunction photovoltaic cells based on crystalline silicon

An approach is proposed to calculate the optimal parameters of silicon-based heterojunction solar cells whose key feature is a low rate of recombination processes in comparison with direct-gap semiconductors. It is shown that at relatively low majority-carrier concentrations (N_d ～ 10¹⁵ cm^–3), the excess carrier concentration can be comparable to or higher than N_d. In this case, the efficiency η is independent of N_d. At higher N_d, the dependence η(N_d) is defined by two opposite trends. One of them promotes an increase in η with N_d, and the other associated with Auger recombination leads to a decrease in η. The optimum value N_d ≈ 2 × 10¹⁶ cm^–3 at which η of such a cell is maximum is determined. It is shown that maximum η is 1.5–2% higher than η at 10¹⁵ cm^–3.     

Low-frequency noise in gallium nitride epitaxial layers with different degrees of order of mosaic structure

The correlation between the noise level 1/f and the degree of mosaic-structure order in gallium nitride epitaxial layers was studied for the first time. Samples with a doping level of N _d ?N _a ≈8×10¹⁶ cm^?3 and a relatively high degree of order were characterized by the Hooge parameter α≈1.5×10^?3. This value is unprecedently low for thin GaN epitaxial films. The Hooge parameter was significantly higher for samples with N _d ?N _a ≈1.1×10¹⁸ cm^?3 and a low degree of order despite the fact that α generally decreases with increasing doping level at the same degree of order. Thus, the degree of mosaic-structure order affects not only the optical and electrical characteristics but also the fluctuation parameters of GaN epitaxial layers.     

Emission sensitization and mechanisms of electron-excitation migration in structures based on III-nitrides doped with rare-earth elements (Eu,Er, Sm)

The effect of doping with Eu, Er, and Sm rare-earth ions on the shape of the luminescence spectrum for heterostructures with GaN/In _x Ga_{1 ? x} N (0.1 < x < 0.4) quantum wells and from p-GaN〈Mg〉/n-GaN and p-AlGaN/n-GaN junctions is investigated. The results of measurements of the electroluminescence of these structures correlate with the previous data on photoluminescence and Mössbauer spectroscopy. It is shown that it is the GaN “yellow” (5000–6000 Å) band that plays the important role in the excitation of intracenter states in the structures with several GaN/InGaN quantum wells doped with Eu and Sm. In this case, Eu is most likely the sensitizer for Sm. Additional introduction of 3d metal (Fe⁵⁷) in p-GaN〈Mg〉/n-GaN:Eu results in the realization of intracenter transitions in Eu³⁺: ⁵ D ₀ → ⁷ F ₁ (6006 Å), ⁵ D ₀ → ⁷ F ₂ (6195 Å), ⁵ D ₀ → ⁷ F ₃ (6627 Å), and ⁵ D ₁ → ⁷ F ₄ (6327 Å) due to the occurrence of new, efficient channels of excitation transfer to intracenter states and in the effect of Fe on the local environment of rare-earth ions including due to the f–d hybridization enhancement.     

Anti-stokes luminescence of Zn<Subscript>0.75</Subscript>Cd<Subscript>0.25</Subscript>S microcrystals annealed in the presence of oxygen

The nature of anti-Stokes luminescence centers excited in the temperature range 77–300 K by light with wavelengths from 620 to 710 nm and intensities in the range 10¹⁵–10¹⁶ photons/cm² in Zn_0.75Cd_0.25S microcrystals annealed in the presence of oxygen has been investigated. It is shown that the centers of two-photon excitation of this luminescence are clusters of native metal oxides (ZnO) _n and (CdO) _n , whose energy levels in the Zn_0.75Cd_0.25S band gap are 1.70–1.95 eV below the bottom of the conduction band.     

Low-temperature instabilities of the electrical properties of Cd<Subscript>0.96</Subscript>Zn<Subscript>0.04</Subscript>Te:Cl semi-insulating crystals

The electrical properties in the temperature range 295–430 K and low-temperature (4.2 K) photoluminescence of Cd_1?xZn_xTe:Cl semi-insulating crystals grown from melts with a variable impurity content (C _Cl ⁰ = 5 × 10¹⁷–1 × 10¹⁹ cm^?3) are investigated. Nonequilibrium processes leading to a decrease in carrier concentration are observed in all the samples at low temperatures (T = 330–385 K). These changes are reversible. The activation energy of these processes E _a is found to be 0.88 eV. As with semi-insulating CdTe:Cl, the observed phenomena can be explained by a change in the charge state of background copper atoms: Cu_Cd ? Cu_i. The introduction of Zn changes the ratio of the concentrations of shallow-level donors Cu_i and Cl_Te from their levels in the initial material.     

Single-Crystal NdBa<Subscript>2</Subscript>Cu<Subscript>3</Subscript>O<Subscript>7–<Emphasis Type="Italic">x</Emphasis></Subscript> Films for Microwave Electronics

The growth of single-crystal films of high-temperature superconductors of the NdBa₂Cu₃O_7–x composition with a thickness of 1–1.5 μm on Al₂O₃ + CeO₂ substrates during the laser spraying is investigated. Technological conditions of the epitaxial growth of the films with a temperature of superconducting transition of 95 K and a critical current of more than 10⁶ A/cm² at the temperature of liquid nitrogen are determined. It is shown that the structure of fabricated NdBa₂Cu₃O_7–x films is more perfect and homogeneous than the structure of YBa₂Cu₃O_7–x films widely used in microwave electronics.     

A 4<Emphasis Type="Italic">H</Emphasis>-SiC<Emphasis Type="Italic">p-i-n</Emphasis> diode fabricated by a combination of sublimation epitaxy and CVD

The possibility of fabricating heavily doped (N _a ?N _d ≥ 1 × 10¹⁹ cm_?3) p⁺-4H-SiC layers on CVD-grown lightly doped n-4H-SiC layers by sublimation epitaxy has been demonstrated. It is shown that a Au/Pd/Ti/Pd contact, which combines a low specific contact resistance (～2 × 10^?5 Ω cm²) with high thermal stability (up to 700°C), is the optimal contact to p-4H-SiC. The p-n structures obtained are used to fabricate packaged diodes with a breakdown voltage of up to 1400 V.     

Influence of the order-disorder transition in the crystal electron subsystem on the electron density at lattice sites

The temperature dependence of the Mössbauer spectrum centroid S of ⁶⁷Zn²⁺ impurity atoms at the copper and yttrium sites of YBa₂Cu₃O_6.9, YBa₂Cu₃O_6.6, YBa₂Cu₄O₈, Nd_1.85Ce_0.15CuO₄, La_1.85Sr_0.15CuO₄, HgBa₂CuO₄, HgBa₂CaCu₂O₆, Bi₂Sr₂CaCu₂O₈, and Tl₂Ba₂CaCu₂O₈ compounds at temperatures T>T _c (T _c is the superconducting transition temperature) is controlled by a second-order Doppler shift. The value of S in the temperature range T<T _c is affected by the energy-band mechanism associated with the formation of Cooper pairs and their Bose condensation. A relationship between the electron density at the metal site of the crystal and its superconducting transition temperature is found. In the case of compounds containing two structurally nonequivalent sites for copper atoms, a change in the electron density caused by the Bose condensate of Cooper pairs is shown to be different for these sites. The experimental temperature dependence of the superconducting electron fraction conforms to a similar dependence following from the Bardeen-Cooper-Schrieffer theory for all the sites under study.     

Effect of the Pressure of Working Gas on the Microcrystalline Structure and Magnetic Properties of the Co Film Deposited with the Aid of Magnetron Sputtering

Effect of argon pressure 0.09 ≤ P ≤ 1 Pa on the microcrystalline structure and magnetic properties of the cobalt films with a thickness of d ≈ 300 nm that are fabricated with the aid of magnetic sputtering on the SiO₂/Si substrates is studied. It is demonstrated that the films obtained at a pressure of Р ≥ 0.2 Pa exhibit mixed crystal phase with close-packed hexagonal (CPH) and face-centered cubic (FCC) lattice with the CPH–Co(002)/FCC–Co(111) texture and column microstructure over thickness. The films deposited at a pressure of Р ≈ 0.09 Pa are characterized by the dominant FCC crystal phase with the FCC–Со(200) texture and inhomogeneous microstructure over thickness: at the interface with the substrate in a layer with a thickness of d₁ ≈ 150 nm, the films exhibit quasi-homogeneous microstructure that is transformed into the granulated microstructure at d > d₁. The films deposited at a pressure of Р ≈ 0.09 Pa have the saturation magnetization that is higher by 30% and the coercive force and linewidth of ferromagnetic resonance that are several times less than those of the film obtained at a pressure of Р ≈ 1 Pa.     

Good Thermal Stability,High Permittivity,Low Dielectric Loss and Chemical Compatibility with Silver Electrodes of Low-Fired BaTiO<Subscript>3</Subscript>–Bi(Cu<Subscript>0.75</Subscript>W<Subscript>0.25</Subscript>)O<Subscript>3</Subscript> Ceramics

(1 ? x)BaTiO₃–xBi(Cu_0.75W_0.25)O₃ [(1 ? x)BT–xBCW, 0 ≤ x ≤ 0.04] perovskite solid solutions ceramics of an X8R-type multilayer ceramic capacitor with a low sintering temperature (900°C) were synthesized by a conventional solid state reaction technique. Raman spectra and x-ray diffraction analysis demonstrated that a systematically structural evolution from a tetragonal phase to a pseudo-cubic phase appeared near 0.03 < x < 0.04. X-ray photoelectron analysis confirmed the existence of Cu⁺/Cu²⁺ mixed-valent structure in 0.96BT–0.04BCW ceramics. 0.96BT–0.04BCW ceramics sintered at 900°C showed excellent temperature stability of permittivity (Δε/ε _25°C ≤ ±15%) and retained good dielectric properties (relative permittivity ～1450 and dielectric loss ≤2%) over a wide temperature range from 25°C to 150°C at 1 MHz. Especially, 0.96BT–0.04BCW dielectrics have good compatibility with silver powders. Dielectric properties and electrode compatibility suggest that the developed materials can be used in low temperature co-fired multilayer capacitor applications.     

Investigation of the ZnS-CdHgTe interface

The ZnS-Cd_xHg_1?xTe interface was investigated using the capacitance-voltage characteristics of MIS structures in experimental samples. During fabrication of the n⁺-p junctions based on p-Cd_xHg_1?xTe, the density of states within the range N _ss =(1–6)×10¹¹ cm^?2 eV^?1 at T=78 K was obtained. The experiments showed that the conditions in which n⁺-p junctions are fabricated only slightly affect the state of the ZnS-CdHgTe interface. The negative voltages of the at bands V _FB , even if immediately after deposition of the ZnS films V _FB >0, point to the enrichment of the ZnS-p-CdHgTe near-surface layer with majority carriers, specifically, holes. This led to a decrease in the leakage current over the surface. During long-term storage (as long as ～15 years) in air at room temperature, no degradation of differential resistance R _d , current sensitivity S _i , and detectivity D* of such n⁺-p junctions with a ZnS protection film was observed.     

Theoretical Study of Electronic Structure and Thermoelectric Properties of Doped CuAlO<Subscript>2</Subscript>

The doping level dependence of thermoelectric properties of delafossite CuAlO₂ has been investigated in the constant scattering time (τ) approximation, starting from the first principles of electronic structure. In particular, the lattice parameters and the energy band structure were calculated using the total energy plane-wave pseudopotential method. It was found that the lattice parameters of CuAlO₂ are a = 2.802 Å and c = 16.704 Å, and the internal parameter is u = 0.1097. CuAlO₂ has an indirect band gap of 2.17 eV and a direct gap of 3.31 eV. The calculated energy band structures were then used to calculate the electrical transport coefficients of CuAlO₂. By considering the effects of doping level and temperature, it was found that the Seebeck coefficient S(T) increases with increasing acceptor doping (A _d) level. The values of S(T) in our experiments correspond to an A _d level at 0.262 eV, which is identified as the Fermi level of CuAlO₂. Based on our experimental Seebeck coefficient and the electrical conductivity, the constant relaxation time is estimated to be 1 × 10^?16 s. The power factor is large for a low A _d level and increases with temperature. It is suggested that delafossite CuAlO₂ can be considered as a promising thermoelectric oxide material at high doping and high temperature.     

Discrete Logarithm Problems with Auxiliary Inputs

Let g be an element of prime order p in an abelian group, and let α∈? _p . We show that if g,g ^α , and \(g^{\alpha^{d}}\) are given for a positive divisor d of p?1, the secret key α can be computed deterministically in \(O(\sqrt{p/d}+\sqrt{d})\) exponentiations by using \(O(\max\{\sqrt{p/d},\sqrt{d}\})\) storage. If \(g^{\alpha^{i}}\) (i=0,1,2,…,2d) is given for a positive divisor d of p+1, α can be computed in \(O(\sqrt{p/d}+d)\) exponentiations by using \(O(\max\{\sqrt{p/d},\sqrt{d}\})\) storage. We also propose space-efficient but probabilistic algorithms for the same problem, which have the same computational complexities with the deterministic algorithm.As applications of the proposed algorithms, we show that the strong Diffie–Hellman problem and related problems with public \(g^{\alpha},\ldots,g^{\alpha^{d}}\) have computational complexity up to \(O(\sqrt{d}/\log p)\) less than the generic algorithm complexity of the discrete logarithm problem when p?1 (resp. p+1) has a divisor d≤p ^1/2 (resp. d≤p ^1/3). Under the same conditions for d, the algorithm is also applicable to recovering the secret key in \(O(\sqrt{p/d}\cdot \log p)\) for Boldyreva’s blind signature scheme and the textbook ElGamal scheme when d signature or decryption queries are allowed.     

Structural and Electrical Properties of Ag/<Emphasis Type="Italic">n</Emphasis>-TiO<Subscript>2</Subscript>/<Emphasis Type="Italic">p</Emphasis>-Si/Al Heterostructure Fabricated by Pulsed Laser Deposition Technique

We have investigated the structural and electrical characteristics of the Ag/n-TiO₂/p-Si/Al heterostructure. Thin films of pure TiO₂ were deposited on p-type silicon (100) by optimized pulsed laser ablation with a KrF-excimer laser in an oxygen-controlled environment. X-ray diffraction analysis showed the formation of crystalline TiO₂ film having a tetragonal texture with a strong (210) plane as the preferred direction. High purity aluminium and silver metals were deposited to obtain ohmic contacts on p-Si and n-TiO₂, respectively. The current–voltage (I–V) characteristics of the fabricated heterostructure were studied by using thermionic emission diffusion mechanism over the temperature range of 80–300 K. Parameters such as barrier height and ideality factor were derived from the measured I–V data of the heterostructure. The detailed analysis of I–V measurements revealed good rectifying behavior in the inhomogeneous Ag/n-TiO₂/p-Si(100)/Al heterostructure. The variations of barrier height and ideality factor with temperature and the non-linearity of the activation energy plot confirmed that barrier heights at the interface follow Gaussian distributions. The value of Richardson’s constant was found to be 6.73 × 10⁵ Am^?2 K^?2, which is of the order of the theoretical value 3.2 × 10⁵ Am^?2 K^?2. The capacitance–voltage (C–V) measurements of the heterostructure were investigated as a function of temperature. The frequency dependence (Mott–Schottky plot) of the C–V characteristics was also studied. These measurements indicate the occurrence of a built-in barrier and impurity concentration in TiO₂ film. The optical studies were also performed using a UV–Vis spectrophotometer. The optical band gap energy of TiO₂ films was found to be 3.60 eV.     

Electron spin resonance in Cd<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Mn<Subscript>x</Subscript>Te and Zn<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Mn<Subscript>x</Subscript>Te compounds

Electron spin resonance in semimagnetic Cd_1?xMn_xTe (0<x<0.7) and Zn_1?xMn_xTe (0<x<0.53) compounds was studied at temperatures of 77 and 300 K. It is found that two types of paramagnetic centers exist in Zn_1?xMn_xTe, one of which is related to Mn²⁺ ions and the other is attributed to structural defects in the crystals.     

Conductivity of Ga<Subscript>2</Subscript>O<Subscript>3</Subscript>–GaAs Heterojunctions

The effect of annealing in argon at temperatures of T_an = 700–900°C on the I–V characteristics of metal–Ga₂O₃–GaAs structures is investigated. Samples are prepared by the thermal deposition of Ga₂O₃ powder onto GaAs wafers with a donor concentration of N _d = 2 × 10¹⁶ cm^–3. To measure theI–V characteristics, V/Ni metal electrodes are deposited: the upper electrode (gate) is formed on the Ga₂O₃ film through masks with an area of S _k = 1.04 × 10^–2 cm² and the lower electrode in the form of a continuous metallic film is deposited onto GaAs. After annealing in argon at T_an ≥ 700°C, the Ga₂O₃-n-GaAs structures acquire the properties of isotype n-heterojunctions. It is demonstrated that the conductivity of the structures at positive gate potentials is determined by the thermionic emission from GaAs to Ga₂O₃. Under negative biases, current growth with an increase in the voltage and temperature is caused by field-assisted thermal emission in gallium arsenide. In the range of high electric fields, electron phonon-assisted tunneling through the top of the potential barrier is dominant. High-temperature annealing does not change the electron density in the oxide film, but affects the energy density of surface states at the GaAs–Ga₂O₃ interface.     

Formation of the low-resistivity compound Cu<Subscript>3</Subscript>Ge by low-temperature treatment in an atomic hydrogen flux

The systematic features of the formation of the low-resistivity compound Cu₃Ge by low-temperature treatment of a Cu/Ge two-layer system in an atomic hydrogen flux are studied. The Cu/Ge two-layer system is deposited onto an i-GaAs substrate. Treatment of the Cu/Ge/i-GaAs system, in which the layer thicknesses are, correspondingly, 122 and 78 nm, in atomic hydrogen with a flux density of 10¹⁵ at cm² s^–1 for 2.5–10 min at room temperature induces the interdiffusion of Cu and Ge, with the formation of a polycrystalline film containing the stoichiometric Cu₃Ge phase. The film consists of vertically oriented grains 100–150 nm in size and exhibits a minimum resistivity of 4.5 µΩ cm. Variations in the time of treatment of the Cu/Ge/i-GaAs samples in atomic hydrogen affect the Cu and Ge depth distribution, the phase composition of the films, and their resistivity. Experimental observation of the synthesis of the Cu₃Ge compound at room temperature suggests that treatment in atomic hydrogen has a stimulating effect on both the diffusion of Cu and Ge and the chemical reaction of Cu₃Ge-compound formation. These processes can be activated by the energy released upon the recombination of hydrogen atoms adsorbed at the surface of the Cu/Ge/i-GaAs sample.     

Thermodynamic stability of bulk and epitaxial CdHgTe,ZnHgTe, and MnHgTe alloys

The thermodynamic stability of Cd_1?xHg_xTe, Mn_xHg_1?xTe, and Zn_xHg_1?xTe alloys is studied. Calculations performed in the context of the δ lattice-parameter model indicate that CdHgTe and ZnHgTe alloys are stable over the entire range of compositions at typical growth temperatures. At the same time, a miscibility gap is found in Mn_xHg_1?xTe at 0.33 < x < 1 at T = 950 K, which is consistent with the known experimental data. It is shown that the biaxial strains observed in Mn_xHg_1?xTe/CdTe and Mn_xHg_1?xTe/Cd_0.96Zn_0.04Te thin epitaxial films lead to a narrowing of the miscibility gap and to insignificant lowering of critical temperatures.