Electrodeposition of <Emphasis Type="Italic">p</Emphasis>-Type Sb<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Te<Subscript><Emphasis Type="Italic">y</Emphasis></Subscript> Thermoelectric Films

Thermoelectric Sb _x Te _y films were potentiostatically electrodeposited in aqueous nitric acid electrolyte solutions containing different concentrations of TeO₂. Stoichiometric Sb _x Te _y films were obtained by applying a voltage of −0.15 V versus saturated calomel electrode (SCE) using a solution consisting of 2.4 mM TeO₂, 0.8 mM Sb₂O₃, 33 mM tartaric acid, and 1 M HNO₃. The nearly stoichiometric Sb₂Te₃ films had a rhombohedral structure, R[`3]m R\bar{3}m , with a preferred orientation along the (015) direction. The films had hole concentration of 5.8 × 10¹⁸/cm³ and exhibited mobility of 54.8 cm²/Vs. A more negative potential resulted in higher Sb content in the deposited Sb _x Te _y films. Furthermore, it was observed that the hole concentration and mobility decreased with increasingly negative deposition potential, and eventually showed insulating properties, possibly due to increased defect formation. The absolute value of the Seebeck coefficient of the as-deposited Sb₂Te₃ thin film at room temperature was 118 μV/K.     

Composition and optical properties of amorphous <Emphasis Type="Italic">a</Emphasis>-SiO<Subscript> <Emphasis Type="Italic">x</Emphasis> </Subscript>:H films with silicon nanoclusters

The phase composition and optical properties of hydrogenated amorphous films of silicon suboxide (a-SiO_x:H) with silicon nanoclusters are studied. Ultrasoft X-ray emission spectroscopy show that silicon- suboxide films with various oxidation states and various amorphous silicon-cluster contents can be grown using dc discharge modulation. In films with an ncl-Si content of ～50%, the optical-absorption edge is observed, whose extrapolation yields an optical band gap estimate of ～3.2–3.3 eV. In the visible region, rather intense photoluminescence bands are observed, whose peak positions indicate the formation of silicon nanoclusters 2.5–4.7 nm in size in these films, depending on the film composition.     

An ultra-low-power CMOS symmetrical OTA for low-frequency <Emphasis Type="Italic">G</Emphasis><Subscript><Emphasis Type="Italic">m</Emphasis></Subscript>-<Emphasis Type="Italic">C</Emphasis> applications

In this paper an ultra-low-power CMOS symmetrical operational transconductance amplifier (OTA) for low-frequency G _m -C applications in weak inversion is presented. Its common mode input range and its linear input range can be made large using DC shifting and bulk-driven differential pair configuration (without using complex approaches). The symmetrical OTA was successfully verified in a standard CMOS 0.35-μm process. The measurements show an open loop gain of 61 dB and a unit gain frequency of 195 Hz with only 800 mV of power supply voltage and just 40 nW of power consumption. The transconductance is 66 nS, which is suitable for low-frequency G _m -C applications.     

Temperature dependence of the band structure of 3<Emphasis Type="Italic">C</Emphasis>, 2<Emphasis Type="Italic">H</Emphasis>, 4<Emphasis Type="Italic">H</Emphasis>, and 6<Emphasis Type="Italic">H</Emphasis> SiC polytypes

The temperature dependences of significant energy extrema at the high-symmetry points Γ, X, L, K, M, A, and H of the Brillouin zone in the cubic and hexagonal modifications of SiC, as well as the energies of the main interband transitions at these points, were calculated for the first time by the empirical-pseudopotential method. The effect of the temperature dependence of the electron-phonon interaction on the crystal band structure was taken into account via the Debye-Waller factors, and the contribution of the linear expansion of the lattice was accounted for via the temperature dependence of the linear-expansion coefficient. The special features of the temperature dependences of the energy levels and of energies of the interband and intraband transitions are analyzed in detail. The results of the calculations are in good agreement with the known experimental data on the characteristics of SiC-based p-n structures operating in the breakdown mode. For example, the temperature coefficient of the energy of the X_1c–X_3c transition, which is responsible for the narrow violet band in the breakdown-electroluminescence spectra of reverse-biased p-n junctions, was found to be significantly smaller than the temperature coefficients for the interband transitions (from the conduction to valence band). This fact is quite consistent with the experimental curve of the temperature coefficient of the emission spectrum, which has a minimum in the same wavelength range.     

Sectoral transition between modes <Emphasis Type="Italic">H</Emphasis><Subscript>10</Subscript> and <Emphasis Type="Italic">H</Emphasis><Subscript>01</Subscript>

The excitation of main parasitic modes E ₁₁, H ₁₁, and H ₂₁, which have cutoff sections in a sectoral transition between modes H ₁₀ and H ₀₁, is investigated. It is shown that, for magnetic modes, including modes H ₁₁ and H ₂₁, it is unnecessary to use the Airy equation and that this circumstance simplifies the design relationships. The energies of these modes are calculated as functions of the transition parameters.     

Epitaxial growth and properties of Mg<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Zn<Subscript>1-<Emphasis Type="Italic">x</Emphasis></Subscript>O films produced by pulsed laser deposition

The Mg _x Zn_1-x O thin films with a Mg content corresponding to x = 0–0.45 are grown by pulsed laser deposition on ablation of ceramic targets. The conditions for epitaxial growth of the films on the single-crystal Al₂O₃ (00.1) substrates are established. The record limit of solubility of Mg in hexagonal ZnO, x = 35 is attained. In this case, the lattice mismatch for the parameter a of the ZnO and Mg_0.35Zn_0.65O films does not exceed 1%, whereas the band gaps of the films differ by 0.78 eV. The surface roughness of the films corresponds to 0.8–1.5 nm in the range of x = 0–0.27.     

Phonon-Assisted Tunneling from <Emphasis Type="Italic">Z</Emphasis><Subscript>1</Subscript>/<Emphasis Type="Italic">Z</Emphasis><Subscript>2</Subscript> in 4H-SiC

n-Type 4H-SiC bulk samples with a net doping concentration of 2.5 × 10¹⁷ cm⁻³ were irradiated at room temperature with 1-MeV electrons. The high doping concentration plus a reverse bias of up to −13 V ensures high electric field in the depletion region. The dependence of the emission rate on the electric field in the depletion region was measured using deep-level transient spectroscopy (DLTS) and double-correlation deep-level transient spectroscopy (DDLTS). The experimental data are adequately described by the phonon-assisted tunneling model proposed by Karpus and Pere.     

Electrical and photoelectric properties of <Emphasis Type="Italic">n</Emphasis>-TiN/<Emphasis Type="Italic">p</Emphasis>-Hg<Subscript>3</Subscript>In<Subscript>2</Subscript>Te<Subscript>6</Subscript> heterostructures

n-TiN/p-Hg₃In₂Te₆ heterostructures are fabricated by depositing a thin n-type titanium nitride (TiN) film onto prepared p-type Hg₃In₂Te₆ plates using reactive magnetron sputtering. Their electrical and photoelectric properties are studied. Dominant charge-transport mechanisms under forward bias are analyzed within tunneling-recombination and tunneling models. The fabricated n-TiN/p-Hg₃In₂Te₆ structures have the following photoelectric parameters at an illumination intensity of 80 mW/cm²: the open-circuit voltage is V_OC = 0.52 V, the short-circuit current is I_SC = 0.265 mA/cm², and the fill factor is FF = 0.39.     

Electrical properties of the <Emphasis Type="Italic">p</Emphasis><Superscript>+</Superscript>-Bi<Subscript>2</Subscript>Te<Subscript>3</Subscript>-<Emphasis Type="Italic">p</Emphasis>-GaSe isotype heterostructure

Electrical properties of a p⁺-Bi₂Te₃-p-GaSe isotype heterostructure fabricated for the first time are reported. A qualitative model is suggested which explains the emergence of negative differential conductivity for a forward-biased structure and for a reverse-biased structure, which is also illuminated.     

Modulation SQUID electronics working with high-<Emphasis Type="Italic">T</Emphasis><Subscript><Emphasis Type="Italic">c</Emphasis></Subscript> SQUIDs in open space

SQUID electronics optimized for operation in unshielded space with dc high-T _c superconducting quantum interference devices (HTS SQUIDs) are developed, manufactured, and studied. The dynamic characteristics of the SQUID electronics are studied with two magnetic-field sensors based on the HTS SQUIDs: a conventional SQUID sensor with a resolution of 100 fT/Hz^1/2 and a supersensitive SQUID sensor with a resolution of 15 fT/Hz^1/2 at frequencies exceeding 10 Hz and a resolution of 30 fT/Hz^1/2 at a frequency of 1 Hz. Stable operation of the magnetometric channel is demonstrated with both SQUID sensors under urban conditions. On the basis of a complex programmable logic device (CPLD), an ac bias can be realized in the SQUID and the modulation signal can be compensated in the feedback, bias-current, and desired-signal circuits. Such a compensation system is the most appropriate and versatile means of providing stable operation of the magnetometric channel in the presence of the SQUID ac bias, regardless of the type of high-temperature sensor and the configuration of the input contacts in the measurement probe.     

Dual-Frequency Behavior of Stacked High <Emphasis Type="Italic">T</Emphasis><Subscript><Emphasis Type="Italic">c</Emphasis></Subscript> Superconducting Microstrip Patches

The dual-frequency behavior of stacked high T _c superconducting rectangular microstrip patches fabricated on a two-layered substrate is investigated using a full-wave spectral analysis in conjunction with the complex resistive boundary condition. Using a matrix representation of each layer, the dyadic Green’s functions of the problem are efficiently determined in the vector Fourier transform domain. The stationary phase method is used for computing the radiation electric field of the antenna. The proposed approach is validated by comparison of the computed results with previously published data. Variations of the lower and upper resonant frequencies, bandwidth and quality factor with the operating temperature are given. Results showing the effects of the bottom patch thickness as well as the top patch thickness on the dual-frequency behavior of the stacked configuration are also presented and discussed. Finally, for a better comprehension of the dual-frequency operation, a comparison between the characteristics of the lower and upper resonances is given.     

Optical storage on the basis of an <Emphasis Type="Italic">n</Emphasis>-InSb-SiO<Subscript>2</Subscript>-<Emphasis Type="Italic">p</Emphasis>-Si heterostructure

The presence of potential barriers and deep traps in n-InSb/SiO₂/p-Si heterostructures makes it possible to realize the optical memory function on the basis of this structure. The maximal memory coefficient measured on the forward current voltage characteristic is as large as ～10⁴. This heterostructure can be used as an optoelectronic memory cell, which provides a means not only for the storage of signals but also for their summation.     

Electrical and gas sensing properties of <Emphasis Type="Italic">por</Emphasis>-Si/SnO<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> nanocomposite layers

The electrical characteristics and chemical reactant sensitivity of layers of heterogeneous nanocomposites based on porous silicon and nonstoichiometric tin oxide por-Si/SnO _x , fabricated by the magnetron sputtering of tin with subsequent oxidation, are studied. It is shown that, in the nanocomposite layers, a system of distributed heterojunctions (Si/SnO _x nanocrystals) forms, which determine the electrical characteristics of such structures. The sensitivity of test sensor structures based on por-Si/SnO _x nanocomposites to NO₂ is determined. A mechanism for the effect of the adsorption of NO₂ molecules on the current-voltage characteristics of the por-Si(p)/SnO _x (n) heterojunctions is suggested.     

Mechanisms of charge transport in anisotype <Emphasis Type="Italic">n</Emphasis>-TiO<Subscript>2</Subscript>/<Emphasis Type="Italic">p</Emphasis>-CdTe heterojunctions

Surface-barrier anisotype n-TiO₂/p-CdTe heterojunctions are fabricated by depositing thin titanium-dioxide films on a freshly cleaved surface of single-crystalline cadmium-telluride wafers by reactive magnetron sputtering. It is established that the electric current through the heterojunctions under investigation is formed by generation-recombination processes in the space-charge region via a deep energy level and tunneling through the potential barrier. The depth and nature of the impurity centers involved in the charge transport are determined.     

<Emphasis Type="Italic">p</Emphasis><Superscript>+</Superscript>-Si-<Emphasis Type="Italic">n</Emphasis>-CdF<Subscript>2</Subscript> heterojunctions

Boron diffusion and the vapor-phase deposition of silicon layers are used to prepare ultrashallow p⁺-n junctions and p⁺-Si-n-CdF₂ heterostructures on an n-CdF₂ crystal surface. Forward portions of the I–V characteristics of the p⁺-n junctions and p⁺-Si-n-CdF₂ heterojunctions reveal the CdF₂ band gap (7.8 eV), as well as allow the identification of the valence-band structure of cadmium fluoride crystals. Under conditions in which forward bias is applied to the p⁺-Si-n-CdF₂ heterojunctions, electroluminescence spectra are measured for the first time in the visible spectral region.     

3<Emphasis Type="Italic">C</Emphasis>-SiC <Emphasis Type="Italic">p-n</Emphasis> structures grown by sublimation on 6<Emphasis Type="Italic">H</Emphasis>-SiC substrates

Sublimation epitaxy in a vacuum has been employed to grow n-and p-type 3C-SiC layers on 6H-SiC substrates. Diodes have been fabricated on the basis of the p-n structure obtained, and their parameters have been studied by measuring their current-voltage and capacitance-voltage characteristics and by applying the DLTS and electroluminescence methods. It is shown that the characteristics of the diodes studied are close to those of diodes based on bulk 3C-SiC. A conclusion is made that sublimation epitaxy can be used to fabricate 3C-SiC p-n structures on substrates of other silicon carbide polytypes.     

Electrical properties of <Emphasis Type="Italic">n-</Emphasis>GaN/<Emphasis Type="Italic">p</Emphasis>-SiC heterojunctions

Epitaxial GaN layers were grown by hydride vapor phase epitaxy (HVPE) on commercial (CREE Inc., USA) p⁺-6H-SiC substrates (Na ? Nd ≈ 7.8 × 10¹⁷ cm^s?3) and n⁺-6H-SiC Lely substrates with a predeposited p⁺-6H-SiC layer. A study of the electrical properties of the n-GaN/p-SiC heterostructures obtained confirmed their fairly good quality and demonstrated that the given combination of growth techniques is promising for fabrication of bipolar and FET transistors based on the n-GaN/p-SiC heterojunctions.     

Electrical properties of <Emphasis Type="Italic">n</Emphasis>-ZnO/<Emphasis Type="Italic">p</Emphasis>-CuO heterostructures

The n-ZnO/p-CuO heterostructure is prepared, and its I-V characteristic is measured. It is shown that the heterostructure conductivity is primarily determined by the CuO layer and the n-ZnO/p-CuO heterojunction itself.     

Preparation and Thermoelectric Properties of LaGd<Subscript>1+<Emphasis Type="Italic">x</Emphasis></Subscript>S<Subscript>3</Subscript> and SmGd<Subscript>1+<Emphasis Type="Italic">x</Emphasis></Subscript>S<Subscript>3</Subscript>

Thermoelectric materials are attractive since they can recover waste heat directly in the form of electricity. In this study, the thermoelectric properties of ternary rare-earth sulfides LaGd_1+x S₃ (x = 0.00 to 0.03) and SmGd_1+x S₃ (x = 0.00 to 0.06) were investigated over the temperature range of 300 K to 953 K. These sulfides were prepared by CS₂ sulfurization, and samples were consolidated by pressure-assisted sintering to obtain dense compacts. The sintered compacts of LaGd_1+x S₃ were n-type metal-like conductors with a thermal conductivity of less than 1.7 W K⁻¹ m⁻¹. Their thermoelectric figure of merit ZT was improved by tuning the chemical composition (self-doping). The optimized ZT value of 0.4 was obtained in LaGd_1.02S₃ at 953 K. The sintered compacts of SmGd_1+x S₃ were n-type hopping conductors with a thermal conductivity of less than 0.8 W K⁻¹ m⁻¹. Their ZT value increased significantly with temperature. In SmGd_1+x S₃, the ZT value of 0.3 was attained at 953 K.