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1.
The effect of annealing in argon at temperatures of Tan = 700–900°C on the IV 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 theIV 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 Tan ≥ 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.  相似文献   

2.
The development of new nanostructured materials based on YBa2Cu3O7–δ, BiFeO3, and Fe3O4 compounds is considered. The structure, morphology, and properties of these materials are studied. The possibilities of fabricating YBa2Cu3O7–δ ceramics with given densities from nanopowders in a single stage by an energy efficient method and growing superconducting films of the same composition on a silicon substrate (on a SiO2 layer) are demonstrated. The technique for fabricating BiFeO3 nanopowder, making it possible to obtain nanostructured ceramics without additional accompanied phases commonly forming during BiFeO3 synthesis is developed. Two methods of the single-stage synthesis of Fe3O4 nanopowder are presented: burning of nitrate-organic precursors and the electrochemical three-electrode method in which one of the electrodes, i.e., an anode containing scrap iron and slurry, is used as an expendable material.  相似文献   

3.
Free-standing, very thin, single-crystal β-gallium oxide (β-Ga2O3) diaphragms have been constructed and their dynamical mechanical properties characterized by noncontact, noninvasive optical measurements harnessing the multimode nanomechanical resonances of these suspended nanostructures. We synthesized single-crystal β-Ga2O3 using low-pressure chemical vapor deposition (LPCVD) on a 3C-SiC epilayer grown on Si substrate at temperature of 950°C for 1.5 h. The synthesized single-crystal nanoflakes had widths of ~ 2 μm to 30 μm and thicknesses of ~ 20 nm to 140 nm, from which we fabricated free-standing circular drumhead β-Ga2O3 diaphragms with thicknesses of ~ 23 nm to 73 nm and diameters of ~ 3.2 μm and ~ 5.2 μm using a dry stamp-transfer technique. Based on measurements of multiple flexural-mode mechanical resonances using ultrasensitive laser interferometric detection and performing thermal annealing at 250°C for 1.5 h, we quantified the effects of annealing and adsorption of atmospheric gas molecules on the resonant characteristics of the diaphragms. Furthermore, we studied the effects of structural nonidealities on these free-standing β-Ga2O3 nanoscale diaphragms. We present extensive characterization of the mechanical and optical properties of free-standing β-Ga2O3 diaphragms, paving the way for realization of resonant transducers using such nanomechanical structures for use in applications including gas sensing and ultraviolet radiation detection.  相似文献   

4.
The method of chloride epitaxy is employed to grow β-Ga2O3 epitaxial layers on a c-sapphire substrate. Purified dry air is used as the source of oxygen. The layers are studied using the methods of X-ray diffraction, optical microscopy, scanning electron microscopy, transmission electron microscopy, and micro-Raman spectroscopy. It is found that the growth plane of the layers is (\(\bar 2\)01), parallel to the substrate surface. The layers consist of separate large crystalline grains of three different in-plane orientations rotated relative to each other in the growth plane by 60°. Misorientation can be caused by the different symmetry of the substrate and the epitaxial layer.  相似文献   

5.
A combined study of the spectral photoluminescence distribution and excitation spectra of photoluminescence in La2S3 · 2Ga2O3 and (La0.97Nd0.03)2S3 · 2Ga2O3 glasses, along with the study of the transmission spectra of these glasses, was carried out. The radiative channel was ascertained to be the main channel for the energy transfer from the host matrix to the Nd3+ ions upon excitation of the glasses with light at a wavelength of the fundamental absorption band. Oxygen centers with the level E c -2.0 eV act as sensitizing agents. The structural disordering of the glass host increases the variance in the magnitude of splitting of the multiplet levels from the 4f electronic states of the Nd3+ ion. This promotes nonradiative relaxation of the electrons from excited states to the laser 4F3/2 level. The (La0.97Nd0.03)2S3 · 2Ga2O3 glasses can be considered as promising laser materials for obtaining the stimulated emission of radiation of Nd3+ ions under an optical pump in the range of the fundamental absorption band of the glass.  相似文献   

6.
7.
Original superconducting quantum interference devices (SQUIDs) with a working temperature of 77 K based on high-temperature superconducting (HTSC) YBa2Cu3O7–x films can be used for the measurement systems of nondestructive testing using magnetic and eddy-current methods. A dynamic range of 120 dB with respect to the amplitude of the measured signal and a spatial resolution of about 10 µm are reached for the measurement system with the HTSC SQUID in which a receiving loop with a size of 50 µm is placed at a distance of about 0.3 mm from the room-temperature object under study. The sensitivity with respect to magnetic field (4 fT/ \(\sqrt {Hz} \) at a temperature of 77 K) of the HTSC SQUID magnetometer with multilayer superconducting flux transformer is sufficient for applications in biomagnetic measurements in magnetocardiography and magnetoencephalography. HTSC SQUID gradiometers with multilayer superconducting flux transformers exhibit stable operation in magnetically unshielded space at a sensitivity of 15 fT/cm \(\sqrt {Hz} \) with respect to the gradient of magnetic field at 77 K. Such a sensitivity is sufficient for the detection of single magnetic particles with a size of about 10 µm at a distance of about 15 mm.  相似文献   

8.
The growth of single-crystal films of high-temperature superconductors of the NdBa2Cu3O7–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 NdBa2Cu3O7–x films is more perfect and homogeneous than the structure of YBa2Cu3O7–x films widely used in microwave electronics.  相似文献   

9.
The possibility of growing single-crystal substitutional (InSb)1 − x (Sn2) x alloy (0 ≤ x ≤ 0.05) on the GaAs substrate by liquid-phase epitaxy from the In solution melt is established. The X-ray diffraction patterns and spectral and current-voltage characteristics of obtained n-GaAs-p-(InSb)1 − x (Sn2) x heterostructures are studied at different temperatures. The lattice parameters of the (InSb)1 − x (Sn2) x alloy are determined. It is found that the forward portion of the current-voltage characteristic of such structures at low voltages (up to 0.7 V) is described by the exponential dependence I = I 0exp(qV/ckT), and at high voltages (V > 0.9 V), there is a portion of sublinear increase in the current with the voltage VV 0exp(Jad). The experimental results are interpreted based on the injection depletion theory. It is shown that the product of mobility of majority carriers by the concentration of deep-level impurities increases as the temperature increases.  相似文献   

10.
The possibility of fabricating a ferroelectric FET based on a Pb(ZrxTi1?x)O3/SnO2 (PZT/SnO2) heterostructure is investigated. Sb-doped epitaxial SnO2/Al2O3 thin film deposited by YAG laser ablation from a metal target is used as the FET channel. The highest obtained electron mobility in the channel is 25 cm2/(V s) at an electron density of 8 × 1019 cm?3. The possibility of growing PZT film directly on SnO2 film using two different techniques, laser ablation and magnetron sputtering, is demonstrated. Both methods have been used in the fabrication of Au/PZT/SnO2 capacitor heterostructures, whose top Au electrode is 250×250 μm2 in size. These cells demonstrate a capacitance of 1000 pF at a 10-V bias and remnant polarization up to 16 μC/cm2. A Au/PZT/SnO2/Al2O3 transistor structure with 94% modulation of the channel current is fabricated. The difference in the channel current under the effect of positive and negative remnant polarization of the undergate ferroelectric is 37%.  相似文献   

11.
Transition metal silicides (TMSis) are attracting increasing interest from the microelectronics and nanoelectronic industries. In this paper, we use the first-principles method to investigate the B-doped mechanism and the influence of B on the electronic properties of α-Nb5Si3. The calculated results show that B-doped Nb5Si3 is thermodynamically stable at the ground state. The calculated electronic structure shows that the thermodynamically stable B-doped Nb5Si3 is attributed to the 3D-network B-Si bonds and B-Nb bond. In particular, B element prefers to occupy B -IT4 site in comparison to other sites. Moreover, the calculated band structure indicates that Nb5Si3 exhibits metallic behavior at the ground state. We find that B-doping can improve charge overlap between conduction band and the valence band, which effectively improves the electronic properties of Nb5Si3.  相似文献   

12.
Thin solid layers that are formed upon heating of the gaseous trimethylbismuth–isopropylselenide–hydrogen system on the (0001) Al2O3 and singular and vicinal (100) GaAs surfaces are studied. The conditions for deposition of metal Bi and phases of Bi4Se3, BiSe, and topological insulator Bi2Se3 using the MOCVD method are determined. Pure metastable phase BiSe is obtained for the first time. Bi2Se3 films with a thickness of no less than 200 nm, a relatively low volume concentration of 3 ×1018 cm–3, and a high mobility of carriers at 300 K (1000 cm2 V–1 s–1) are fabricated.  相似文献   

13.
Oxide thermoelectric materials (Na1−y M y )1.4Co2O4 (M = Sr, Li; y = 0 to 0.4) were prepared by a sol–gel method. The influence of doping on the thermoelectric properties was investigated, and the phase composition was characterized by x-ray diffraction. Experimental results showed that the main crystalline phase of the undoped and Sr/Li-doped samples was γ-Na1.4Co2O4. The thermoelectric properties of Na1.4Co2O4 can be improved slightly by doping with Sr. Doping with Li improves the thermoelectric properties of Na1.4Co2O4. For a doping fraction of y = 0.1, the electrical conductivity of (Na1−y Li y )1.4Co2O4 at 288 K achieves its maximum value of 301.19 (Ω mm)−1. The Seebeck coefficient and power factor of (Na1−y Li y )1.4Co2O4 at 288 K achieve their maximum values of 172.28 μV K−1 and 7.44 mW m−1 K−2 at a doping fraction of y = 0.4.  相似文献   

14.
The effect of the content of CuO additive on the sinterability, phase composition, microstructure, and electrical properties of BaCe0.5Zr0.3Y0.2O3–δ proton-conducting material is studied. Ceramic samples were produced by the citrate–nitrate synthesis method with the addition of 0, 0.25, 0.5, and 1% CuO. It is shown that the relative density of the samples containing 0.5 and 1% CuO is higher than 94% at a sintering temperature of 1450°C, whereas the relative density of the material is no higher than 85% at a lower content of the sintering additive. From the data of X-ray diffraction analysis and scanning electron microscopy, it is established that the introduction of a small CuO content (0.25%) is inadequate for single-phase and high-dense ceramics to be formed. The conductivity and scanning electron microscopy data show that the sample with BaCe0.5Zr0.3Y0.2O3–δ + 0.5% CuO composition possesses high total and ionic conductivities as well as a high degree of microstructural stability after hydrogen reduction of the ceramics. The citrate–nitrate method modified by the introduction of a small CuO content can be recommended for the production of single-phase, gas-tight, and high-conductivity electrolytes based on both BaCeO3 and BaZrO3.  相似文献   

15.
Single crystals of the ternary system Bi2−x Tl x Se3 (nominally x = 0.0 to 0.1) were prepared using the Bridgman technique. Samples with varying content of Tl were characterized by measurement of lattice parameters, electrical conductivity σ ⊥c, Hall coefficient R H(Bc), and Seebeck coefficient ST⊥c). The measurements indicate that incorporation of Tl into Bi2Se3 lowers the concentration of free electrons and enhances their mobility. This effect is explained within the framework of the point defects in the crystal lattice, with formation of substitutional defects of thallium in place of bismuth (TlBi) and a decrease in the concentration of selenium vacancies (VSe + 2 V_{\rm{Se}}^{ + 2} ). The temperature dependence of the power factor σS 2 of the samples is also discussed. As a consequence of the thallium doping we observe a significant increase of the power factor compared with the parent Bi2Se3.  相似文献   

16.
Polycrystalline samples of In4(Se1−x Te x )3 were synthesized by using a melting–quenching–annealing process. The thermoelectric performance of the samples was evaluated by measuring the transport properties from 290 K to 650 K after sintering using the spark plasma sintering (SPS) technique. The results indicate that Te substitution can effectively reduce the thermal conductivity while maintaining good electrical transport properties. In4Te3 shows the lowest thermal conductivity of all compositions tested.  相似文献   

17.
The transmittance spectra of MnIn2S4 and FeIn2S4 ternary compounds and Mn x Fe1 − x In2S4 alloys in the fundamental absorption edge region are studied. The samples were grown by planar melt crystallization. From the experimental spectra, the band gaps of the compounds and their alloys are determined, and the concentration dependence of the alloy band gap on the component content is established. It is found that the band gap nonlinearly varies with the composition parameter x and can be described by a quadratic function.  相似文献   

18.
The transmittance spectra of (CuInSe2)1 − x (2MnSe) x alloy crystals grown by the Bridgman method are studied in the temperature range from 10 to 300 K. For these materials, the band gap and its temperature dependence are determined. It is shown that the band gap decreases with increasing temperature. The dependences of the band gap of the (CuInSe2)1 − x (2MnSe) x alloys on the composition parameter x are plotted.  相似文献   

19.
Nanocrystalline Ni-doped gadolinium oxide (Gd1.90Ni0.10O3?δ, GNO) is synthesized by co-precipitation method. The as-prepared sample is annealed in vacuum at 700°C for 6 h. Analyses of the x-ray diffractogram by Rietveld refinement method, transmission electron microscopy and Raman spectroscopy of GNO recorded at room temperature confirmed the pure crystallographic phase and complete substitution of Ni-ions in Gd2O3 lattice. Magnetization (M) as a function of temperature (T) and magnetic field (H) is measured by a superconducting quantum interference device magnetometer, which suggests the presence of ferromagnetic/antiferromagnetic phases together with a paramagnetic phase. From the M–T curve it can be shown that the ferromagnetic phase dominates over para-/antiferromagnetic phases in the temperature range of 300–100 K, but from 100 K to 50 K, the antiferromagnetic phase dominates over ferro-/paramagnetic phases. Hysteresis loops recorded at different temperatures indicate the presence of weak ferro-/antiferromagnetism, which dominates in the low field region (~ 4000 Oe), above which magnetization increases linearly. The sharp increase of magnetization in M–T curve observed in the temperature range of 50–5 K confirms the presence of dominating ferromagnetic plus paramagnetic phase over antiferromagnetic part. For the first time a combined formula generated from three-dimensional (3D) spin wave model and Johnston formula is proposed to analyze the coexistence of different magnetic phases in different temperature ranges. Interestingly, the combined formula successfully explains the co-existence of different magnetic phases along with their contribution at different temperatures. The onset of ferromagnetism in Gd1.90Ni0.10O3?δ is explained by oxygen vacancy mediated F-centre exchange (FCE) coupling mechanism.  相似文献   

20.
Terahertz (THz) radiation perception using uncooled detectors are gaining importance due to the increasing demands in the areas of military, space, and industrial, medical, and surveillance applications. In spite of the efforts of researchers to fill the THz gap, there exists a need for detectors in the range between 15 THz and 30 THz. In this paper, we discuss the development of bolometric detectors whose performance is enhanced by an optical immersion technique and their characterization in the aforesaid range of frequencies. These detectors are characterized by high specific detectivity (D*) of 1.28?×?109 cmHz1/2 W?1 and high radiometric resolution (noise-equivalent temperature difference?=?26 mK) and are fast enough for bolometric detectors (time constant?=?1.7 ms), which make them suitable for spectroscopic and imaging applications.  相似文献   

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