Frequency and voltage-dependent electrical and dielectric properties of Al/Co-doped PVA/p-Si structures at room temperature

In order to investigate of cobalt-doped interracial polyvinyl alcohol （PVA） layer and interface trap （Dit） effects, A1/p- Si Schottky barrier diodes （SBDs） are fabricated, and their electrical and dielectric properties are investigated at room temperature. The forward and reverse admittance measurements are carded out in the frequency and voltage ranges of 30 kHz-300 kHz and -5 V-6 V, respectively. C-V or er-V plots exhibit two distinct peaks corresponding to inversion and accumulation regions. The first peak is attributed to the existence of Dit, the other to the series resistance （Rs）, and interfacial layer. Both the real and imaginary parts of dielectric constant （er and err） and electric modulus （Mr and Mrr）, loss tangent （tan~）, and AC electrical conductivity （aac） are investigated, each as a function of frequency and applied bias voltage. Each of the M~ versus V and Mrr versus V plots shows a peak and the magnitude of peak increases with the increasing of frequency. Especially due to the Dit and interfacial PVA layer, both capacitance （C） and conductance （G/w） values are strongly affected, which consequently contributes to deviation from both the electrical and dielectric properties of A1/Co-doped PVA/p-Si （MPS） type SBD. In addition, the voltage-dependent profile of Dit is obtained from the low-high frequency capacitance （CLF-CHF） method.     

Electrical and dielectric properties of Al/p-Si and Al/perylene/p-Si type diodes in a wide frequency rangeElectrical and dielectric properties of Al/p-Si and Al/perylene/p-Si type diodes in a wide frequency rangeElectrical and dielectric properties of Al/p-Si and Al/perylene/p-Si type diodes in a wide frequency range

The perylene （C20H12） layer effect on the electrical and dielectric properties of Al/p-Si （MS） and Al/perylene/p-Si （MPS） diodes have been investigated and compared in the frequency range of 0.7 kHz-2 MHz. Experimental results show that C-V characteristics give an anomalous peak for two structures at low frequencies due to interface states （Nss） and series resistance （Rs）. The increases in C and G/o3 at low frequencies confirm that the charges at interface can easily follow an ac signal and yield excess capacitance and conductance. The frequency-dependent dielectric constant （er） and dielectric loss （e＇） are subtracted using C and G/co data at 1.5 V. The eI and e＂ values are found to be strongly dependent on frequency and voltage, and their large values at low frequencies can be attributed to the excess polarization coming from charges at traps. Plots of ln（o＇ac）-ln（w） for two structures have two linear regions, with slopes of 0.369 and 1.166 for MS, and of 0.077 and 1.061 for MPS, respectively. From the C 2-V characteristics, the doping acceptor atom concentration （NA） and barrier height （,~） for Schottky barrier diodes （SBDs） 1.303 ~ 1015 cm-3, and 1.10 and I. 13 eV, respectively. of MS and MPS types are also obtained to be 1.484 ~ 1015 and     

Structure distortion,optical and electrical properties of ZnO thin films co-doped with Al and Sb by sol-gel spin coating

ZnO thin films co-doped with Al and Sb with different concentrations and a fixed molar ratio of AlCl 3 to SbCl 3 at 1:2, are prepared by a sol-gel spin-coating method on glass annealed at 550°C for 2 h in air. The x-ray diffraction results confirm that the ZnO thin films co-doped with Al and Sb are of wurtzite hexagonal ZnO with a very small distortion, and the biaxial stresses are 1.03×10 8 , 3.26×10 8 , 5.23×10 8 , and 6.97×10 8 Pa, corresponding to those of the ZnO thin films co-doped with Al and Sb in concentrations of 1.5, 3.0, 4.5, 6.0 at% respectively. The optical properties reveal that the ZnO thin films co-doped with Al and Sb have obviously enhanced transmittance in the visible region. The electrical properties show that ZnO thin film co-doped with Al and Sb in a concentration of 1.5 at% has a lowest resistivity of 2.5Ω·cm.     

In situ electrical resistance and activation energy of solid C6o under high pressure

The in situ electrical resistance and transport activation energies of solid C60 fullerene have been measured under high pressure up to 25 GPa in the temperature range of 300-423 K by using a designed diamond anvil cell. In the experiment, four parts of boron-doped diamond films fabricated on one anvil were used as electrical measurement probes and a W-Ta thin film thermocouple which was integrated on the other diamond anvil was used to measure the temperature. The current results indicate that the measured high-pressure resistances are bigger than those reported before at the same pressure and there is no pressure-independent resistance increase before 8 GPa. From the temperature dependence of the resistivity, the C60 behaviors as a semiconductor and the activation energies of the cubic C60 fullerene are 0,49, 0.43, and 0.36 eV at 13, 15, and 19 GPa, respectively.     

Comparison between N2 and O2 anneals on the integrity of an Al2O3/SiaN4/SiO2/Si memory gate stack

In this paper the endurance characteristics and trap generation are investigated to study the effects of different postdeposition anneals （PDAs） on the integrity of an Al2O3/Si3N4/SiOz/Si memory gate stack. The flat-band voltage （Vfb） turnarounds are observed in both the programmed and erased states of the N2-PDA device. In contrast, this turnaround is observed only in the erased state of the O2-PDA device. The Vfb in the programmed state of the O2-PDA device keeps increasing with increasing program/erase （P/E） cycles. Through the analyses of endurance characteristics and the low voltage round-trip current transients, it is concluded that in both kinds of device there are an unknown type of pre-existing characteristic deep traps and P/E stress-induced positive oxide charges. In the O2-PDA device two extra types of trap are also found： the pre-existing border traps and the P/E stress-induced negative traps. Based on these four types of defects we can explain the endurance characteristics of two kinds of device. The switching property of pre-existing characteristic deep traps is also discussed.     

Electrical peculiarities in Al/Si/Ge/…/Ge/Si and Al/SiGe/Si structures

The current–voltage (I–V) and capacitance–voltage (C–V) behaviour of different Si/Ge multilayers and SiGe single layers prepared on p-type Si substrates by magnetron sputtering and annealing, has been studied in the temperature range of 80–320 K by using Al Schottky contacts as test structures. Although a significant influence of the microstructure of the Si/Ge multilayers and SiGe layers was obtained on the electrical behaviour of the structures, the structures exhibited similar specific features.     

Analysis of flatband voltage shift of metallhigh-k/Si02/Si stack based on energy band alignment of entire gate stack

A theoretical model of flatband voltage （VFB） of metal/high-k/Si02/Si stack is proposed based on band alignment of entire gate stack, i.e., the VFB is obtained by simultaneously considering band alignments of metal/high-k, high-k/SiO2 and SiO2/Si interfaces, and their interactions. Then the VFB of TiN/HfO2/SiO2/Si stack is experimentally obtained and theoretically investigated by this model. The theoretical calculations are in good agreement with the experimental results. Furthermore, both positive VFB shift of TiN/HfO2/SiO2/Si stack and Fermi level pinning are successfully interpreted and attributed to the dielectric contact induced gap states at TiN/HfO2 and HfO2/SiO2 interfaces.     

Sputtering pressure influence on growth morphology,surface roughness,and electrical resistivity for strong anisotropy beryllium film

The strong anisotropy beryllium （Be） films are fabricated at different sputtering pressures by direct current magnetron sputtering. With the increase of pressure, the deposition rate of Be film first increases, and when the pressure exceeds 0.8 Pa, it gradually descends. The X-ray diffraction analysis indicates that Be film is of α-Be phase, its surface always reveals the （101） crystal plane possessing the low surface energy. As for the growth morphology of Be film, the surface is mainly characterized by the fibrous grains, while the cross section shows a transition from a columnar grain to a mixed grain consisting of a cone-shaped grain and a columnar grain as the sputtering pressure increases. The large grain fraction decays exponentially from 75.0% to 59.3% with the increase of sputtering pressure p, which can improve the grain size uniformity. The surface roughness increases due to the insufficient atom diffusion, which is comparable to its decrease due to the etching effect at p 〈 0.8 Pa, while it increases drastically at p 〉 0.8 Pa, and this increase is dominated by the atom diffusion. The electrical resistivity values of Be films range from 1.7 μΩ m to 2.7 μΩ m in the range 0.4 Pa-1.2 Pa, which is 50 times larger than the bulk resistivity.     

Improved mobility of AIGaN channel heterojunction material using an AIGaN/GaN composite buffer layer

The quality of an A1GaN channel heterojunction on a sapphire substrate is massively improved by using an A1- GaN/GaN composite buffer layer. We demonstrate an A10.4Gao.6N/AI0.18Ga0.82N heterojunction with a state-of-the-art mobility of 815 cm2/（V.s） and a sheet resistance of 890Ω/口 under room temperature. The crystalline quality and the electrical properties of the A1GaN heterojunction material are analyzed by atomic force microscopy, high-resolution X-ray diffraction, and van der Pauw Hall and capacitance-voltage （C-V） measurements. The results indicate that the improved electrical properties should derive from the reduced surface roughness and low dislocation density.     

Forward and reverse electron transport properties across a CdS/Si multi-interface nanoheterojunction

The electron transport behavior across the interface plays an important role in determining the performance of op- toelectronic devices based on heterojunctions. Here through growing CdS thin film on silicon nanoporous pillar array, an untraditional, nonplanar, and multi-interface CdS/Si nanoheterojunction is prepared. The current density versus voltage curve is measured and an obvious rectification effect is observed. Based on the fitting results and model analyses on the forward and reverse conduction characteristics, the electron transport mechanism under low forward bias, high forward bias, and reverse bias are attributed to the Ohmic regime, space-charge-limited current regime, and modified Poole-Frenkel regime respectively. The forward and reverse electrical behaviors are found to be highly related to the distribution of inter- facial trap states and the existence of localized electric field respectively. These results might be helpful for optimizing the preparing procedures to realize high-performance silicon-based CdS optoelectronic devices.     

Analysis of optoelectronic properties of TiO_2 nanowiers/Si heterojunction arrays

The optoelectronic properties of n-TiO2NW/p-Si heterojunction fabricated by depositing TiO2 nanowires on a p-Si substrate are studied. Under excitation at a wavelength of 370 nm, the TiO2 nanowires produce a light emission at 435 nm due to the emission of free excitons. The I-V characteristics are measured to investigate the heterojunction effects under the dark environment and ultraviolet （UV） illumination, n-TiOzNW/p-Si has a p-n junction formed in the n-TiOz/p-Si beterojunction. TiO2NW/Si photodiode produces a pbotocurrent larger than dark current under UV illumination. It is observed that UV photons are absorbed in TiO2 and the heterojunction shows a 0.034-A/W responsivity at 4-V reverse bias.     

Electrical and dielectric characterization of Au/ZnO/n-Si device depending frequency and voltage

Au/Zn O/n-type Si device is obtained using atomic layer deposition(ALD) for Zn O layer, and some main electrical parameters are investigated, such as surface/interface state(Nss), barrier height(Φb), series resistance(Rs), donor concentration(Nd), and dielectric characterization depending on frequency or voltage. These parameters are acquired by use of impedance spectroscopy measurements at frequencies ranging from 10 k Hz to 1 MHz and the direct current(DC) bias voltages in a range from-2 V to +2 V at room temperature are used. The main electrical parameters and dielectric parameters,such as dielectric constant(ε"), dielectric loss(ε"), loss tangent(tan δ), the real and imaginary parts of electric modulus(M and M), and alternating current(AC) electrical conductivity(σ) are affected by changing voltage and frequency. The characterizations show that some main electrical parameters usually decrease with increasing frequency because charge carriers at surface states have not enough time to fallow an external AC signal at high frequencies, and all dielectric parameters strongly depend on the voltage and frequency especially in the depletion and accumulation regions. Consequently, it can be concluded that interfacial polarization and interface charges can easily follow AC signal at low frequencies.     

Theoretical investigation on the electronic structure,elastic properties, and intrinsic hardness of Si2N20

According to the density functional theory we systematically study the electronic structure, the mechanical prop- erties and the intrinsic hardness of Si2N2O polymorphs using the first-principles method. The elastic constants of four Si2N2O structures are obtained using the stress-strain method. The mechanical moduli （bulk modulus, Young’s mod-ulus, and shear modulus） are evaluated using the Voigt-Reuss-Hill approach. It is found that the tetragonal Si2N2O exhibits a larger mechanical modulus than the other phases. Some empirical methods are used to calculate the Vickers hardnesses of the Si2N2O structures. We further estimate the Vickers hardnesses of the four Si2N2O crystal structures, suggesting all Si2N2O phases are not the superhard compounds. The results imply that the tetragonal Si2N2O is the hardest phase. The hardness of tetragonal Si2N2O is 31.52 GPa which is close to values of β-Si3N4 and γ-Si3N4.     

Preparation of multi-walled carbon nanotube–Fe composites and their application as light weight and broadband electromagnetic wave absorbers

Multi-walled carbon nanotube （MWCNT）-Fe composites were prepared via the metal organic chemical vapor deposi- tion by depositing iron pentacarbonyl on the surface of MWCNTs. The structural and morphological analyses demonstrated that Fe nanoparticles were deposited on the surface of the MWCNTs. The electromagnetic properties of the MWCNTs were significantly changed, and the absorbing capacity evidently improved after the Fe deposition on the MWCNT surface. A minimum reflection loss of -29.4 dB was observed at 8.39 GHz, and the less than -10 dB bandwidth was about 10.6 GHz, which covered the whole X band （8.2-12.4 GHz） and the whole Ku band （12.4-18 GHz）, indicating that the MWCNT-Fe composites could be used as an effective microwave absorption material.     

Different temperature dependence of carrier transport properties between AlxGal-xN/InyGal-yN/GaN and Alx Gal-xN/GaN heterostruct ures

The temperature dependence of carrier transport properties of Alx Gal-xN/InyGal-yN/CaN and AlzGal-xN/GaN heterostructures has been investigated. It is shown that the Hall mobility in Alo.25Gao.75N/Ino.03Gao.97N/GaN heterostructures is higher than that in Alo.25Gao.75N/GaN heterostructures at temperatures above 500 K, even the mobility in the former is much lower than that in the latter at 300 K. More importantly, the electron sheet density in Alo.25Gao.75N/Ino.03Gao.97N/GaN heterostructures decreases slightly, whereas the electron sheet density in Al0.25Gao.75N/CaN heterostructures gradually increases with increasing temperature above 500 K. It is believed that an electron depletion layer is formed due to the negative polarization charges at the Iny Can-yN/GaN heterointerface induced by the compressive strain in the InyCal-yN channel, which effectively suppresses the parallel conductivity originating from the thermal excitation in the underlying GaN layer at high temperatures.     

Electrical properties of bio-SiC and Si components of the SiC/Si biomorphic composite

The electrical resistivity ρ of bio-SiC, a highly porous cellular material prepared from a biomorphic composite SiC/Si based on white eucalyptus wood through the chemical removal of silicon, was measured in the temperature range 5–100 K. The electrical resistivity of bio-SiC was found to be anisotropic along and across the cellular pores. The activation energy of charge transfer in bio-SiC was estimated. The measured values of ρ for the SiC/Si biomorphic composite and bio-SiC were used to determine the electrical resistivity ρ and the carrier concentration in silicon, which is one of the constituents of the composite.     

Magnetization study of polycrystalline YBa2AlxCu(3−x)O7−δ (x = 0.05, 0.10 and 0.20) compounds

Superconductivity in polycrystalline YBa₂Al_xCu_(3−x)O_7−δ materials was characterized by dynamic AC and quasistatic DC magnetometry. Intragranular persistent current density and low-loss intergranular critical current density were deduced using DC and AC techniques, respectively. Addition of aluminum produced modest increases in the intragranular persistent current for x < 0.2, but drastically reduced the intergranular critical current density for x = 0.2. The critical temperature T_c for superconductivity decreased only 4% for Al content up to x = 0.2.     

Electrical and optical properties of Sb-doped ZnO thin films synthesized by sol–gel method

Sb-doped ZnO thin films with different values of Sb content （from 0 to 1.1 at.%） are deposited by the sol-gel dip- coating method under different sol concentrations. The effects of Sb-doping content, sol concentration, and annealing ambient on the structural, optical, and electrical properties of ZnO films are investigated. The results of the X-ray diffraction and ultraviolet-visible spectroscopy （UV-VIS） spectrophotometer indicate that each of all the films retains the wurtzite ZnO structure and possesses a preferred orientation along the c axis, with high transmittance （〉 90%） in the visible range. The Hall effect measurements show that the vacuum annealed thin films synthesized in the sol concentration of 0.75 mol/L each have an adjustable n-type electrical conductivity by varying Sb-doping density, and the photoluminescence （PL） spectra revealed that the defect emission （around 450 nm） is predominant. However, the thin films prepared by the sol with a concentration of 0.25 mol/L, despite their poor conductivity, have priority in ultraviolet emission, and the PL peak position shows first a blue-shift and then a red-shift with the increase of the Sb doping content.     

Electrical and magnetic properties of polyaniline/Fe3O4 nanostructures

We report on electrical and magnetic properties of polyaniline (PANI) nanotubes (150 nm in diameter) and PANI/Fe₃O₄ nanowires (140 nm in diameter) containing Fe₃O₄ nanoparticles with a typical size of 12 nm. These systems were prepared by a template-free method. The conductivity of the nanostructures is 10⁻¹–10⁻² S/cm; and the temperature dependent resistivity follows a ln ρT^−1/2 law. The composites (6 and 20 wt% of Fe₃O₄) show a large negative magnetoresistance compared with that of pure PANI nanotubes and a considerably lower saturated magnetization (M_s=3.45 emu/g at 300 K and 4.21 emu/g at 4 K) compared with the values measured from bulk magnetite (M_s=84 emu/g) and pure Fe₃O₄ nanoparticles (M_s=65 emu/g). AC magnetic susceptibility was also measured. It is found that the peak position of the AC susceptibility of the nanocomposites shifts to a higher temperature (>245 K) compared with that of pure Fe₃O₄ nanoparticles (190–200 K). These results suggest that interactions between the polymer matrix and nanoparticles take place in these nanocomposites.     

Theoretical study on K, L, and M X-ray transition energies and rates of neptunium and its ions

The transition energies and electric dipole （El） transition rates of the K, L, and M lines in neutral Np have been theoretically determined from the MultiConfiguration Dirac-Fock （MCDF） method. In the calculations, the contributions from Breit interaction and quantum electrodynamics （QED） effects （vacuum polarization and self-energy）, as well as nu- clear finite mass and volume effects, are taken into account. The calculated transition energies and rates are found to be in good agreement with other experimental and theoretical results. The accuracy of the results is estimated and discussed. Furthermore, we calculated the transition energies of the same lines radiating from the decaying transitions of the K-, L-, and M-shell hole states of Np ions with the charge states Np1＋ to Np6＋ for the first time. We found that for a specific line, the corresponding transition energies relating to all the Np ions are almost the same; it means the outermost electrons have a very small influence on the inner-shell transition processes.