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.     

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.     

A vacancy model of the heteropolytype epitaxy of SiC

A model for the transformation of SiC polytypes occurring during the growth of an epitaxial layer is suggested that is based on the variation over time of the concentration of carbon vacancies in a transition layer. Experimental data are analyzed in terms of this model. It is shown that the parameter η=Gτ/L _T (L _T is the thickness of the transition layer, G is the film growth rate, and τ is the lifetime of a vacancy in the transition layer) is invariant with respect to the method and temperature of the growth of the epitaxial layer. This parameter is determined only by the concentration of carbon vacancies in the substrate and in the film.     

Surface roughness and magnetic properties of Co/SiO<Subscript>2</Subscript>/Si(100) polycrystalline films deposited via DC magnetron sputtering

For polycrystalline films of cobalt that have the thickness t ≈ 1.3–133 nm and that are deposited via DC magnetron sputtering on SiO₂(0.1 μm)/Si(100) substrates, surface-roughness root-mean-square amplitude σ and surface correlation length ξ, which characterize the roughness of film surfaces, as well as saturation magnetization 4πM ₀, width of ferromagnetic-resonance line ΔH, coercitivity H _C, and saturation fields H _S, are studied as functions of film thickness t. It is shown that the behavior of dependences H _C(t) and H _S(t) coincides with the behavior of dependence σ(t)/t, whereas the behavior of 4πM ₀(t) depends on ratio t/σ(t). The dependence of the FMR line width on the film thickness, ΔH(t), is characterized by a minimum of ΔH ≈ 60 Oe present in the region of thicknesses of 30 to 60 nm. The behavior of dependence ΔH(t) is determined by ratio σ(t)/t at small thicknesses t ≤ 5 nm and by the behavior of σ(t) at t ≥ 5 nm.     

CdTe as a passivating layer in CdTe/HgCdTe heterostructures

CdTe/Hg_{1 ? x} Cd _x Te heterostructures are studied. In the structures, CdTe is used as a passivating layer deposited as a polycrystal or single crystal on a single-crystal Hg_{1 ? x} Cd _x Te film. The film and a passivating layer were obtained in a single technological process of molecular beam epitaxy. The structure of passivating layers was studied by reflection high-energy electron diffraction, and the effect of the structure of the passivating layer on the properties of the active layer was studied by X-ray diffractometry. Mechanical properties of heterostructures were studied by the microhardness method. Electrical and photoelectrical parameters of the Hg_{1 ? x} Cd _x Te films are reported.     

Electrical characteristics of Au/<Emphasis Type="Italic">n</Emphasis>-GaAs structures with thin and thick SiO<Subscript>2</Subscript> dielectric layer

The aim of this study, to explain effects of the SiO₂ insulator layer thickness on the electrical properties of Au/n-GaAs Shottky barrier diodes (SBDs). Thin (60 Å) and thick (250 Å) SiO₂ insulator layers were deposited on n-type GaAs substrates using the plasma enganced chemical vapour deposition technique. The current-voltage (I–V) and capacitance-voltage (C-V) characteristics have been carried out at room temperature. The main electrical parameters, such as ideality factor (n), zero-bias barrier height (? _Bo ), series resistance (R _s ), leakage current, and interface states (N _ss ) for Au/SiO₂/n-GaAs SBDs have been investigated. Surface morphologies of the SiO₂ dielectric layer was analyzed using atomic force microscopy. The results show that SiO₂ insulator layer thickness very affects the main electrical parameters. Au/n-GaAs SBDs with thick SiO₂ insulator layer have low leakage current level, small ideality factor, and low interface states. Thus, Au/n-GaAs SBDs with thick SiO₂ insulator layer shows better diode characteristics than other.     

Anisotropy of the magnetocapacitance of structures based on PbSnTe:In/BaF<Subscript>2</Subscript> films

The angular dependences of the capacitance of structures based on PbSnTe:In films in a magnetic field B ≤ 4 T at various bias voltages, which have a distinct anisotropic pattern in the magnetic-field direction with capacitance modulation approximately by a factor of 1.5–2, are studied experimentally at T = 4.2 K. The data obtained are compared with the experimental anisotropic angular dependences of the space-charge-limited current with current modulation up to a factor of 10²–10⁴ or greater. A qualitative model of the results obtained is considered.     

Optical properties of hybrid quantum-well–dots nanostructures grown by MOCVD

The deposition of In _x Ga_1–x As with an indium content of 0.3–0.5 and an average thickness of 3–27 single layers on a GaAs wafer by metalorganic chemical vapor deposition (MOCVD) at low temperatures results in the appearance of thickness and composition modulations in the layers being formed. Such structures can be considered to be intermediate nanostructures between ideal quantum wells and quantum dots. Depending on the average thickness and composition of the layers, the wavelength of the photoluminescence peak for the hybrid InGaAs quantum well–dots nanostructures varies from 950 to 1100 nm. The optimal average In _x Ga_1–x As thicknesses and compositions at which the emission wavelength is the longest with a high quantum efficiency retained are determined.     

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.     

Effect of the Ti-Nanolayer Thickness on the Self-Lift-off of Thick GaN Epitaxial Layers

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.     

Study of the correlation properties of the surface structure of <Emphasis Type="Italic">nc</Emphasis>-Si/<Emphasis Type="Italic">a</Emphasis>-Si:H films with different fractions of the crystalline phase

The correlation properties of the structure of nc-Si/a-Si:H films with different volume fractions of the crystalline phase are studied using 2D detrended fluctuation analysis. Study of the surface relief of experimental samples showed that with increasing in volume fraction of the crystalline phase in the nc-Si/a-Si:H films, the size and number of nanoclusters on their surface grow. The size of Si nanocrystals in the a-Si:H matrix (6–8 nm) indicates the formation of coarse nanoclusters due to the self-organization of Si nanocrystals in groups under laser radiation. According to 2D detrended fluctuation analysis data, the number of correlation vectors (harmonic components) in the nc-Si/a-Si:H film structure increased with an increase in the nanocrystal fraction in the films.     

Dependence of the electrical parameters of MBE-grown Cd<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Hg<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>Te films on the level of doping with indium

Dependences of the minority-carrier lifetime and electron mobility in Cd _x Hg_{1 ? x} Te films on their indium-doping level are studied. Films with x ≈ 0.22 grown by molecular-beam epitaxy on GaAs substrates were in situ doped with indium across their entire thickness. The temperature dependences of the lifetime were studied in the temperature range 77–300 K. The decrease in the lifetime, observed as the doping level increases, is governed by the mechanism of Auger recombination. As the doping level becomes higher, the mobility decreases in qualitative agreement with theoretical calculations.     

Size Effects in Transport Properties of PbSe Thin Films

This paper presents an overview and analysis of our earlier obtained experimental results on the dependences of kinetic properties of single PbSe quantum wells and PbSe-based superlattices on the PbSe layer thickness d. The observed oscillatory character of these dependences is attributed to quantum size effects due to electron or hole confinement in quantum wells. Some general regularities and factors that determine the character of these quantum size effects are established. The influence of the oxidation processes and doping on the d-dependences of the transport properties is revealed. A periodic change in the conductivity type related to quantum size oscillations is detected. It is shown that the experimentally determined values of the oscillation period Δd are in good agreement with the results of theoretical calculations based on the model of a rectangular quantum well with infinitely high walls, taking into account the dependence of the Fermi energy ε _F on d and the availability of subbands below ε _F. It is established that the Δd value for the superlattices is practically equal to the Δd value observed for the single PbSe thin film.     

Crystalline SiN<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> Ultrathin Films Grown on AlGaN/GaN Using <Emphasis Type="Italic">In Situ</Emphasis> Metalorganic Chemical Vapor Deposition

Surface passivation by SiN _x films is indispensable for high-power operation of AlGaN/GaN heterojunction field-effect transistors (HFETs) since it can effectively suppress collapse in the drain current. So far, the plasma-enhanced chemical vapor deposition technique has been used for the SiN _x deposition; however, possible damage induced by the plasma processing may affect direct-current performance or reliability. In this paper, we present subsequent deposition of SiN _x ultrathin films on AlGaN/GaN in the same metalorganic chemical vapor deposition reactor. It is experimentally found that this in situ SiN _x passivation doubles the sheet carrier density at the AlGaN/GaN interface from that of the unpassivated sample. High-resolution cross-sectional transmission electron microscopy reveals that in situ SiN _x is crystallized on the AlGaN layer as island-like structures via the Stranski-Krastanov growth mode. The lattice constants of in situ SiN _x are estimated to be a ≈ 3.2 Å and c ≈ 2.4 Å, which are quite different from those of well-known Si₃N₄ crystal structures. First-principles calculation predicts that the crystal structure of in situ SiN _x is the defect wurtzite structure, which well explains the experimental results. The passivation technique using crystalline SiN _x films would be promising for high-power and high-frequency applications of AlGaN/GaN HFETs.     

Effects of Nb Content on the Ferroelectric and Dielectric Properties of Nb/Nd-Co-doped Bi<Subscript>4</Subscript>Ti<Subscript>3</Subscript>O<Subscript>12</Subscript> Thin Films

Nd/Nb-co-substituted Bi_3.15Nd_0.85Ti_3?x Nb _x O₁₂ (BNTN _x , x = 0.01, 0.03, 0.05 and 0.07) thin films were grown on Pt/Ti/SiO₂/Si (100) substrates by chemical solution deposition. The effects of Nb content on the micro-structural, dielectric, ferroelectric, leakage current and capacitive properties of the BNTN _x thin films were investigated. A low-concentration substitution with Nb ions in BNTN _x can greatly enhance its remanent polarization (2P _r) and reduce the coercive field (2E _c) compared with those of Bi₄Ti₃O₁₂ (BIT) thin film. The highest 2P _r (71.4 μC/cm²) was observed in the BNTN_0.03 thin film when the 2E _c was 202 kV/cm. Leakage currents of all the films were on the order of 10^?6 to 10^?5 A/cm², and the BNTN_0.03 thin film has a minimum leakage current (2.1 × 10^?6 A/cm²) under the high electric field (267 kV/cm). Besides, the C–V curve of the BNTN_0.03 thin film is the most symmetrical, and the maximum tunability (21.0%) was also observed in this film. The BNTN_0.03 thin film shows the largest dielectric constant and the lowest dielectric loss and its maximum Curie temperature is 410 ± 5°C.     

Photoconductivity of thin <Emphasis Type="Italic">a</Emphasis>-Si:H films

Photoelectric and optical properties of a-Si:H films with a thickness of 60–100 nm were studied. Temperature dependences of photoconductivity in the temperature range 130–440 K and spectral dependences of the absorption coefficient near the absorption edge were measured. The results of comparative measurements of the room-temperature conductivity and the absorption coefficient in the defect-related subgap spectral range (photon energy hν = 1.2 eV) indicate that the recombination of nonequilibrium carriers and, accordingly, the photoconductivity of a-Si:H films with a thickness of ～100 nm are determined by the defect concentration in the films.     

Characterization of HgCdTe Films Grown on Large-Area CdZnTe Substrates by Molecular Beam Epitaxy

Recent advances in growth of Hg_1?x Cd _x Te films on large-area (7 cm × 7.5 cm) CdZnTe (CZT) substrates is presented. Growth of Hg_1?x Cd _x Te with good uniformity on large-area wafers is achieved using a Riber 412 molecular beam epitaxy (MBE) tool designed for growth of Hg_1?x Cd _x Te compounds. The reactor is equipped with conventional CdTe, Te, and Hg sources for achieving uniform exposure of the wafer during growth. The composition of the Hg_1?x Cd _x Te compound is controlled in situ by employing a closed-loop spectral ellipsometry technique to achieve a cutoff wavelength (λ _co) of 14 μm at 78 K. We present data on the thickness and composition uniformity of films grown for large-format focal-plane array applications. The composition and thickness nonuniformity are determined to be <1% over the area of a 7 cm × 7.5 cm wafer. The films are further characterized by Fourier-transform infrared spectroscopy, optical microscopy, and Hall measurements. Additionally, defect maps show the spatial distribution of defects generated during the epitaxial growth of the Hg_1?x Cd _x Te films. Microdefect densities are in the low 10³ cm^?2 range, and void defects are below 500 cm^?2. Dislocation densities less than 5 × 10⁵ cm^?2 are routinely achieved for Hg_1?x Cd _x Te films grown on CZT substrates. HgCdTe 4k × 4k focal-plane arrays with 15 μm pitch for astronomical wide-area infrared imagers have been produced using the recently developed MBE growth process at Teledyne Imaging Sensors.     

Possibility of the use of intermediate carbidsiliconoxide nanolayers on polydiamond substrates for gallium nitride layers epitaxy

The results of using carbidsiliconoxide (a-C:SiO1_.5) films with a thickness of 30–60 nm, produced by the pyrolysis annealing of oligomethylsilseskvioksana (CH₃–SiO_1.5)_n with cyclolinear (staircased) molecular structure, as intermediate films in the hydride vapor phase epitaxy of gallium nitride on polycrystalline CVD-diamond substrates are presented. In the pyrolysis annealing of (CH₃–SiO_1.5)_n films in an atmosphere of nitrogen at a temperature of 1060°C, methyl radicals are carbonized to yield carbon atoms chemically bound to silicon. In turn, these atoms form a SiC monolayer on the surface of a-C:SiO_1.5 films via covalent bonding with silicon. It is shown that GaN islands grow on such an intermediate layer on CVD-polydiamond substrates in the process of hydride vapor phase epitaxy in a vertical reactor from the GaCl–NH₃–N₂ gas mixture.     

Thermoelectric effects in nanoscale layers of manganese silicide

The values of the thermoelectric power, layer resistivity and thermal conductivity of a Mn _x Si_1–x nanoscale layer and Mn _x Si_1–x/Si superlattice on silicon depending on the growth temperature in the range T = 300–600 K are found experimentally. The contribution of the nanoscale film and substrate to the thermoelectric effect is discussed. The thermoelectric figure of merit of a single manganese-ssilicide layer, superlattice, and layer/substrate system is estimated. The largest figure of merit ZT = 0.59 ± 0.06 is found for Mn_0.2Si_0.8 at T = 600 K.     

Characteristics of the Schottky barriers of two-terminal thin-film Al/nano-Si film/ITO structures

The temperature dependence of the Schottky-barrier height and series resistance of two-terminal thin-film Al/nano-Si film/ITO structures are determined from the current—voltage (I–V) characteristics in the temperature range of 20–150°C. It is found that the form of the I–V characteristic at all investigated temperatures can be described by a model of two Schottky diodes connected back-to-back. For these diodes, the general formula is obtained, which allows the construction of functions approximating experimental curves with high accuracy. Based on this formula, a computational model is built, which generalizes the theoretical data obtained by S.K. Cheung and N.W. Cheung widely used for analyzing the I–V characteristics of single Schottky diodes. A technique is developed for calculating the Schottky-barrier heights in a system of two Schottky diodes connected back-to-back, their ideality factors, and the series resistance of the system. It is established that the barrier heights in the investigated temperature range are ~1 eV. According to the temperature dependence of the barrier height, such large values result from the presence of a SiO _x (0 ≤ x ≤ 2) oxide layer at the nanoparticle boundaries. Charge carriers can overcome this layer by means of thermal excitation or tunneling. It is established that the intrinsic Schottky-barrier height of the Al/nc-Si film and nc-Si film/ITO junctions is ~0.1 eV. The activation dependences of the series resistance of the Al/nc-Si film/ITO structures and impedance spectra show that combined electric-charge transport related to ionic and electronic conductivity takes place in the structures under study. It is shown that the contribution of the electronic conductivity to the total transport process increases as the sample temperature is raised.