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Purpose Heat exchangers (HEs) which provide heat transfer and transfer energy through direct or indirect contact between fluids have an essential role in many processes as a part of various industries from pharmaceutical production to electronic devices. Using nanofluid as working fluid and integrating different types of turbulators could be used to upgrade the thermal effectiveness of HEs. Recently, to obtain more increment in thermal effectiveness, hybrid nanofluids are used that are prepared by mixing two or more various nanoparticles. The purpose of this experimental and numerical study is investigating different scenarios for improving the effectiveness of a concentric U-tube type HE. Design/methodology/approach In the numerical section of this study, different turbulator modifications, including circular and quarter circular rings, were modeled to determine the effect of adding turbulator on thermal performance. In addition, Al2O3/water and SiO2/water single and Al2O3–SiO2/water hybrid nanofluids were experimentally tested in an unmodified concentric U-tube HE in two different modes, including counter flow and parallel flow. Al2O3–SiO2/water hybrid nanofluid was prepared at 2% (wt./wt.) particle ratio and compared with Al2O3/water and SiO2/water single type nanofluids at same particle ratios and with distilled water. Findings Numerical modeling findings exhibited that integrating turbulators to the concentric tube type HE caused to raise in the effectiveness by improving heat transfer area. Also, experimental results indicated that using both hybrid and single type nanofluids notably upgraded the thermal performance of the concentric U-tube HE. Integrating turbulators cannot be an effective alternative in a concentric U-tube type HE with lower diameter because of raise in pressure drop. Numerically achieved findings exhibited that using quarter circular turbulators decreased pressure drop in comparison with circular turbulators. According to the experimental outcomes, using hybrid Al2O3–SiO2/water nanofluid leads to obtain more thermal performance in comparison with single type nanofluids. The highest increment in overall heat transfer coefficient of HE by using Al2O3–SiO2/water nanofluid achieved as 58.97% experimentally. Originality/value The overall outcomes of the current research exhibited the positive impacts of using hybrid nanofluid and integrating turbulators. In this empirical and numerical survey, numerical simulations were performed to specify the impact of applying different turbulators and hybrid nanofluid on the flow and thermal characteristics in a concentric U-tube HE. The achieved outcomes exhibited that using hybrid nanofluid can notably increase the thermal performance with negligible pressure drop in comparison with two different turbulator modifications.

In this study, the electrical and dielectric characteristics of the Au/(RuO2:PVC)/n-Si structures were analyzed using the impedance spectroscopy method, including capacitance/conductance (C - G/ω) measurements in wide voltage and frequency ranges (±4 V, 5 kHz – 5 MHz) at room temperature. The main electrical parameters such as concentration of donor atoms (ND), diffusion potential (VD), depletion layer thickness (WD), Fermi energy level (EF), barrier height (ΦB), and maximum electric field (Em) were extracted for each measured frequency. The ΦB, WD, and EF values are increasing with increased frequency, while ND and Em exponentially decrease. The surface-states (NSS) were evaluated using the low–high-frequency capacitance technique. Furthermore, the basic dielectric parameters such as tangent-loss (tan δ), electrical conductivity (σac), real and imaginary parts of ε*, electric-modulus (M*), and complex impedance (Z*) were investigated. The obtained results indicate that the NSS, and RuO2:PVC organic interlayer are more effective on C and G/ω measurements.

The RuO2-doped organic polymer composite structure was used as the interface to study the photodiode properties of a Schottky structure. Some basic electrical and optoelectrical parameters of the structure interlaid with RuO2:PVC were investigated using the I–V characteristics in the dark and under defnite illuminations. The values of saturation current (I0), barrier height (ΦB0) at zero-bias, ideality factor (n), series and shunt resistances (Rs and Rsh) were calculated by using diferent methods such as thermionic emission, Ohm’s law, Cheung and Norde functions. They were found to be intensely depend on illumination levels and voltage. Forward bias I–V data were used to obtain energy-dependent profles of interface-states (Nss) for each illumination level. Moreover, the open-circuit voltage (Voc), short circuit current (Isc), flling factor (FF), and efciency (η) of the fabricated Schottky structure were found as 0.118 V, 6.4 μA, 46%, and 0.088% under 50 mW/cm−2, respectively. According to the fndings, the RuO2:PVC organic interlayer is light-sensitive and can thus be used in optoelectronic applications, such as photodetectors and photodiodes.

Sensitivity ( S ) and drive mode are crucial issues for the vertical metal-oxide-semiconductor (MOS) type diode applied in temperature sensing. In this study, experimentally, we indicated that the S values of the Ni(50 nm) - Au(100 nm) /Ga2O3/ p -Si vertical MOS type diode, using the measured capacitance–voltage ( Cm – V ) outputs, are obtained with a novel drive mode. We applied the constant capacitance mode to drive the silicon thermo-diodes as well as constant current mode, and constant voltage mode, which are known as two different methods in the literature. Meanwhile, the S value is 21.2 mV/K at 1 nF. This value is the highest value proven in the literature excepting the cryogenic temperature region, and near room temperature. This study provided an original structure for the silicon thermo-diodes and a novel way to drive them.

The possible current-conduction mechanism (CCMs) of the Au/CoSO4-PVP/n-Si junctions was investigated using temperature-dependence current-voltage (I-V) experiments over 100-360 K. The experimental results showed that the value of BH increases approximately linearly with increasing temperature. Such positive temperature coefficient (alpha = Delta phi(B0)/Delta T) is in agreement with the reported negative temperature coefficient of the bandgap of Si (= - 0.473 meV/K). The (n(ap)(-1)-1) vsq/2kT curves have different characters in two temperature ranges due to having separate two barrier distributions. The rho(2)and rho(3)values obtained from intercept and slope of these curves as 0.521 V and 0.011 V for 240-360 K temperature range and 0.737 V and 0.004 V for the 100-220 K range. This results show that the high temperature region with smaller rho(2)and larger rho(3)voltage deformation coefficients has a wider and greater of the barrier height distribution than the second region. As an evidence for the Gaussian distribution, the phi(B0)and standard deviation (sigma(0)) were derived from the intercept and slope of the phi(B0)-q/2kT curves as 1.14 eV and 0.163 V at high temperatures and 0.62 eV and 0.088 V at low temperatures. The Richardson constant obtained as 102 A/cm(2)K(2)for 240-360 K temperature range using standard deviation value which is similar to the theoretical Richardson constant value of silicon (112 A/cm(2)K(2)). For each temperature, the profile ofN(ss)vs (E-c-E-ss) was provided using the voltage-dependent effective barrier height (phi(e)) value. It was observed that these surface conditions decreased with increasing temperature.

© 2022In this work, the temperature-dependent (80–360 K) dielectric properties of the Au/ZnO-PVA/n-Si structure was investigated employing capacitance-voltage (C–V) and conductance-voltage (G/ω-V) experiments at 1 MHz. The results indicate that all electrical and dielectric variables in these structures are forcefully dependent on temperature. Also, using the interlayer ZnO-PVA nanocomposite has caused changes to these parameters. Because of the presence of series resistance, the amount of C and G/ω increases as the temperature rises. The values of EF increase with temperature, whereas the values of barrier height decrease from 1.045 eV to 0.943 eV, and the value of α extract from ΦB-T plot is obtained −3.5 × 10−4 eV/K that is approximately equal to the silicon temperature coefficient. The value of activation energy is obtained 0.04 eV which is a modest amount obtained from the conduction procedure's contribution to the boundary grains.

The vertical Schottky barrier diode (SBD)-based temperature sensors with the drive modes are a significant issue with more advantageous than the on-chip sensor. The sensitivity (S) and the current conduction mechanisms (CCMs) of the vertical cadmium telluride (CdTe):polyvinyl pyrolidone (PVP)/p-Si SBD were studied experimentally over the range of 80–340 K and compared with that of the lateral and vertical sensors. It is shown that the low and moderated voltages of the CdTe:PVP/p-Si corresponding two linear regions of the current–voltage (I–V) outputs are around 0.1–0.3 and 0.4–0.65 V, respectively. The variation of Schottky barrier height (BH; Bo) and ideality factor (n) with temperature was obtained according to two linear regions. Energy dispersion of the interface traps (Nss) with changing temperature is additionally analyzed quantitatively. It is concluded that the thermionic-emission (TE) theory with double-Gaussian distribution (GD) is the dominant mechanism resulting the I–V characteristics of the vertical CdTe:PVP/p-Si SBD in this study. Moreover, in the constant current, the S values at the drive current of 10, 20, and 50 μA were resulting in a range of −1.6 to −1.8 mV/K.

Amorphous gallium oxide (Ga2O3) thin films were investigated as gate dielectrics for electronic device applications using plasma-enhanced atomic layer deposition. The structural and morphological properties as well as the electrical and dielectric behaviors of Ga2O3 thin films were explored. The surface morphology of the amorphous Ga2O3 thin film was highly smooth with root mean square of 0.55 nm and low defect density, which were visible to atomic force microscopy. The grazing incidence X-ray diffraction pattern showed no discernible peak, indicating that the film was amorphous. The X-ray photoelectron spectroscopy depth-profiling analysis showed that the Ga/O ratio was 0.76, slightly more than the optimum 2/3 ratio (0.67). The temperature-dependent current-voltage characteristics of the Au/Ni/Ga2O3/p-Si structure revealed that ideality factor and barrier height values decreased and increased with increasing temperature, respectively, demonstrating their high temperature dependency. Regardless of the applied frequency, Ga2O3 thin films exhibited a good dielectric constant of about similar to 9 at zero bias voltage. The comprehensive capacitance-voltage analysis showed low trap densities of about 10(12) eV(-1) cm(-2) at the Ga2O3-p-Si interface.

To determine the influence of the thin polymer interface film on the electrical and dielectric characteristics of the Al/p-Si MS structure, the Graphene doped (Bi2Te3-Bi2O3-TeO2): PVP film was deposited on the silicon substrate using the spin-coating method. The mean size of these nanostructures was found less than 50 nm using the XRD method. EDX profile shows that the structure of Bi2Te3-Bi2O3-TeO2 consists of the bismuth (Bi), tellurium (Te), and oxygen (O) atoms and also not consists of other impurities or compounds. The key electrical and dielectric parameters of metal-semiconductor (MS) and metal-polymer/semiconductor nanocomposite structures were examined using I-V and Z-f analyses. The values of saturation-current (I-0), barrier-height (BH) at zero-bias (phi(B0)), ideality factor (n), series and shunt resistances (R-s, R-sh) data for both structures were derived from the I-V experiments at +/- 6 V voltage scales and compared with them. The energy distributions of interface state density (D-it) were also acquired from the voltage-dependent phi(B)(V) and n(V) data. Finally, the frequency dependence of complex dielectric (epsilon* = epsilon ' - j epsilon '') and electric modulus (M* = M ' + jM ''), dielectric loss tangent (tan delta), and ac electrical conductivity (sigma(ac)) values were evaluated from the C-f and G/omega-f experiments for both structures at 10(2)-10(6) Hz frequency scale. The results depict that the Bi2Te3-Gr: PVP organic layer improves the quality of the MS structure as it reduces the leakage current, n, and D-it and increases the R-sh, BH, and epsilon '.

In this study, HfAlO3 ternary alloy thin film was grown on n-type silicon using the atomic layer deposition method. The current transport mechanisms in the (Au/Ni/HfAlO3/n-Si junction were examined over a wide temperature range (80-360 K). The values obtained for the ideality factor (n) varied from 22.93 to 3.94 and the barrier height at zero bias (Phi(B0)) ranged from 0.221 eV to 0.821 eV as the temperature changed from 80 to 360 K. The Phi(B0)-n and Phi B-30-q/2 kT characteristics were investigated to explain the higher n values and non-ideal behavior of the Richardson curves. Two linear regions were found at low temperatures (LTs; 80-180 K) and high temperatures (HTs; 200-360 K), which indicated the presence of a Gaussian distribution barrier height and the average barrier heights ((Phi) over bar (B0)) were identified. The values obtained for (Phi) over bar (B0 )were 0.734 eV for LTs and 1.125 eV for HTs, and the values of sigma(s) were 0.085 V for LTs and 0.140 V for HTs. The values obtained for N-ss decreased as the temperature increased and they varied between similar to 10(12) and 10(13) eV(-1) cm(-2). Finally, the dielectric behavior and conductivity of the (Au/Ni)/HfAlO3/n-Si junction were investigated at frequencies between 5 kHz and 2 MHz at room temperature. The values determined for epsilon' and epsilon '' at -1 V and 5 kHz were 2.1 and 3.53, respectively.

The current-voltage (I-V) and capacitance-voltage (C-V) behaviors of the (Au/Ni)/HfAlO3/n-Si (MIS) junctions at room temperature under white light with various intensities were investigated. The ln(I)-Vcurves show two linear behavior regions at about 1 V before and after the point of intersection that can be defined as two separate current-conduction (CMs) Mechanisms. The values of the ideality factor (n) and the zero-bias barrier height (phi(B0)) were extracted using the slope and intercept of the ln(I)-Vcurve before and after the intersection point based on lighting power. Although the phi(B0)values decrease with increasing light power,nincreases for two regions, and there is a strong linear relationship between them. The values of photo-current (I-ph) increase with the increasing lighting power due to the formation of electron-hole pairs. The slope of the double-logarithmicI(ph)-Pwas changed from 0.422 to 0.852, respectively, at - 2 V and - 9 V, which indicates the ongoing distribution ofN(ss). In addition, the profile of surface states (N-ss) ionized by light was obtained from the capacitance measured in dark and under lighting at 1 MHz. TheN(ss)-Vcurve has two characteristic peaks that correspond to the region of depletion and accumulation due to a special distribution ofN(ss)and their restructuring and reordering under the effects of lighting and an electric field.

© 2018 Elsevier B.V.In this study, simple ultrasound-assisted method was used for prepare the composite of (Cu-doped PVA) interfacial layer between metal and semiconductor (Al/p-Si). The scanning electron microscopy (SEM) images of the prepared (Cu-doped PVA) nanocomposites have shown an uniform fish scale shape, which are about 100 nm long and several tens of nm in width. Both the Al/p-Si (MS) and Al/(Cu-PVA)/p-Si (MPS) structures were fabricated on the same Si wafer to investigate the effect of this polymer layer on the electrical characteristics by using the current-voltage (I-V) and capacitance/conductance-voltage (C/G-V) measurements at room temperature. The values of reverse-saturation current (Io), ideality factor (n) and zero-bias barrier height (ΦBo) were obtained from the liner part of the forward bias I-V plot as 6.6 × 10−10 A, 3.67 and 0.84 eV for MS structure and 1.82 × 10−8 A, 4.18 and 0.76 eV for MPS structure, respectively. MPS structure has a good rectifier behavior with low leakage current in comparison to the MS structure. The high values of n was attributed to the barrier inhomogeneity at Al/p-Si, special density distribution of Nss at (Cu-PVA)/p-Si interface and both the existence of native SiO2 and deposited of (Cu-doped PVA) interlayer at M/S interface. The energy dependent values of Nss were obtained from the forward bias I-V data and they ranged from the 1.85 × 1013 eV−1cm−2 (0.60 eV -Ev) to 7.40 × 1013 eV−1cm−2 (0.40 eV - Ev) for MS structure and 9.81 × 1012 eV−1cm−2 (0.67 eV -Ev) to 5.26 × 1013 eV−1cm−2 (0.47 eV -Ev) for the MPS structure. Experimental results show that the (Cu-PVA) interlayer can be successfully used instead of traditional insulator layer because of the saturation of dangling bonds.

Au/ZnO/n-Si (MIS) structures were fabricated by using the RF sputtering method and their complex dielectric constant (epsilon*= epsilon'-j epsilon"), electric modulus (M*=M' + jM") and electrical conductivity (sigma = sigma(dc) + sigma(ac)) values were investigated as a function of frequency (0.7 kHz-1 MHz) and voltage (- 6 - ( + 6 V)) by capacitance-voltage (C-V) and conductance-voltage (G/omega-V) measurements to get more information on the conduction mechanisms and formation of barrier height between Au and n-Si. The In sigma-Inf plots have two different regions corresponding to low-intermediate and high frequencies. Such behavior of In sigma-Inf plots shows that the existence of two different conduction mechanisms (CMs) at low-intermediate and high frequencies. Moreover, the reverse bias saturation current (I-0), ideally factor (n), barrier height (Phi(B0)) were determined from the forward bias I-V data and they were found as a strong function of temperature. The value of n especially at low temperature is considerably higher than unity. The values of (Phi) over bar (B0) and standard deviation(sigma(s)) were found from the intercept and slope of (Phi) over bar (B0)-q/2kT plots as 0.551 eV and 0.075 V for the region I (80-220 K) and 1.126 eV and 0.053 V for the region II (220-400 K), respectively. The values of (Phi) over bar (B0) and effective Richardson constant (A*) were found from slope and intercept of activation energy plots as 0.564 eV and 101.084 Acm(-2) K-2 for the region I and 1.136 eV and 41.87 Acm(-2) K-2 for the region II, respectively. These results confirm that the current-voltage-temperature (I-VT) characteristics of the fabricated Au/ZnO/n-Si SBDs can satisfactorily be explained on the basis of TE theory with double GD of the BHs.

The aim of this study is to improve the electrical property of Ag/n-Si metal–semiconductor (MS) structure by growing an Ru-doped PVP interlayer between Ag and n-Si using electrospinning technique. To illustrate the utility of the Ru-doped PVP interface layer, current–voltage (I–V) characteristics of Ag/n-Si (MS) and Ag/Ru-doped PVP/n-Si metal–polymer–semiconductor (MPS) structures was carried out. In addition, the main electrical parameters of the fabricated Ag/Ru-doped PVP/n-Si structures were investigated as a function of frequency and electric field using impedance spectroscopy method (ISM). The capacitance–voltage (C–V) plot showed an anomalous peak in the depletion region due to the special density distribution of interface traps/states (Dit/Nss) and interlayer. Both the values of series resistance (Rs) and Nss were drawn as a function of voltage and frequency between 0.5 kHz and 5 MHz at room temperature and they had a peak behavior in the depletion region. Some important parameters of the sample such as the donor concentration atoms (ND), Fermi energy (E F ), thickness of the depletion region (WD), barrier height (Φ B0 ) and R s were determined from the C−2 versus V plot for each frequency. The values of N D , W D , Φ B0 and R s were changed from 1 × 1015 cm−3, 9.61 × 10−5 cm, 0.94 eV and 19,055 Ω (at 0.5 kHz) to 0.13 × 1015 cm−3, 27.4 × 10−4 cm, 1.04 eV and 70 Ω (at 5 MHz), respectively. As a result of the experiments, it is observed that the change in electrical parameters becomes more effective at lower frequencies due to the Nss and their relaxation time (τ), dipole and surface polarizations.

In order to interpret the electrical characteristics of fabricated Au/ZnO/n-Si structures as a function of frequency and voltage well, their capacitance–voltage (C–V) and conductance–voltage (G/ω–V) measurements were carried out in a wide range of frequencies (0.7 kHz–2 MHz) and voltages (± 6 V) by 50 mV steps at room temperature. Both the C–V and G/ω–V plots have reverse, depletion, and accumulation regions such as a metal–insulator/oxide semiconductor (MIS or MOS) structures. The values of doped-donor atoms (N D), Fermi energy level (E F), barrier height (ΦB), and series resistance (R s) of the structure were obtained as a function of frequency and voltage. While the value of N D decreases with increasing frequency almost as exponentially, the value of depletion width (W D) increases. The values of C and G/ω increase with decreasing frequency because the surface states (N ss) are able to follow the alternating current (AC) signal, resulting in excess capacitance (C ex) and conductance (G ex/ω), which depends on their relaxation time and the frequency of the AC signal. The voltage-dependent profiles of N ss were obtained from both the high–low frequency capacitance and Hill-Colleman methods. The other important parameter R s of the structure was also obtained from the Nicollian and Brews methods as a function of voltage.