Value Of Φb Research Articles

Large-area vertical-geometry Pt/(010) β-Ga2O3 Schottky barrier diodes and their temperature-dependent electrical properties

Herein, vertical-geometry Pt/(010) β-Ga2O3 Schottky barrier diodes (SBDs) with various large areas (2.25 × 10−2, 4 × 10−2 to 6.25 × 10−2 cm2) were fabricated on (010) orientation β-Ga2O3 substrates. The electrical properties of different area diodes and the uniformity of diodes with the same area were analyzed. The rectifying ratio of all diodes was determined to be larger than 108 at the bias of ±2 V. The current-voltage (I–V) characteristics of SBD with an area of 2.25 × 10−2 cm2 were investigated in detail from 300 to 450 K. The parameters of the diodes show a strong dependence on temperature, including ideality factor (n), on-resistance (Ron), turn-on voltage (Von), and the Schottky barrier (Φb). The results indicate that a dominant inhomogeneous Schottky barrier exists at the Pt/β-Ga2O3 interface. Such large-area devices exhibit that the value of n is close to 1 and the value of Φb was 1.09 eV at zero bias. In addition, the Von remains low and the stability remains good even after the tests at 450 K. These results indicate that we have successfully fabricated large-area SBDs with excellent performances. This work may contribute to further understanding of the performance of β-Ga2O3 diodes in large areas and harsh environments.

The role of non-homogeneous barrier on the electrical performance of 15R–SiC Schottky diodes grown by in-situ RF sputtering

In the present work, we have demonstrated the impact of barrier inhomogeneities on the electrical characteristics of silicon carbide (SiC) based Schottky barrier diodes (SBDs). Ohmic and Schottky contacts were deposited on RF sputtered 15R–SiC film under optimized growth conditions. Forward biased current-voltage (I–V) measurement in the temperature range of 300–420 K was employed to extract the diode parameters (barrier height, ideality factor, and Richardson constant), considering the thermionic emission (TE) as dominant charge transport mechanism. The obtained value of barrier height φB and ideality factor n exhibited anomalies as compared to theoretically predicted values. It was attributed to the co-existence of multiple charge transport mechanism owing to defect induced lateral barrier inhomogeneities at the metal-semiconductor interface. Further, Gaussian distribution of φB, as established by Warner and Guttler was incorporated along with TE model to analyze the temperature dependent I–V data to understand the non-ideality in diode parameters. Eventually, the obtained diode parameters as per the modified charge transport mechanism were found to be in close alignment with the predicted values.

Double-exponential current–voltage (I–V) and negative capacitance (NC) behavior of Al/(CdSe-PVA)/p-Si/Al (MPS) structure

In this study, I–V and C–V characteristics of the Al/(CdSe-PVA)/p-Si/Al (MPS) structure have been investigated the by taking into account double-exponential I–V and NC behavior. The structural characterization of CdSe nanocrystals were analyzed by X-ray diffraction (XRD), scanning electron micros-copy (SEM), and energy dispersive X-ray (EDX) techniques. These results show that the prepared CdSe consists of spherical monodispersed nanocrystalites of about 200 nm; aggregated in the form of poly-dispersive nanoclusters of arbitrary shape with the size in the range of 150-300 nm and they are in good agreement with those estimated from the XRD pattern. The forward bias LnI–V plot of the MPS structure has two linear parts which are called low bias Region 1 (R1:0.25-0.65 V) and moderate bias Region 2 (R2:0.70-1.20 V). The ideality factor (n) and barrier height (BH:ΦB0) were found to be 9.38 and 0.61 eV for R1 and 6.51 and 0.65 eV for R2, respectively. The current conduction/transport mechanism (CCM/CTM) are also defined by forward I–VLn(I)–V and reverse bias In(IR)–VR1/2 plots. I–VLn(I)–V plot has also two linear parts which are also called (R1:-3.02/-0.29) and (R2:-0.10/1.60) obey I ~ Vm law. The slope (m) of them was found to be 1.63 and 4.57 which are corresponding to ohmic and trap-charge limited current (TCLC) mechanisms, respectively. Moreover, the value of ΦB(C–V) was found from the linear part of C−2-V plot as 0.79 eV which is higher than the obtained forward bias lnI–V plot due to the nature of measured method.

Experimental study of the shear strength of soil from the Heifangtai Platform of the Loess Plateau of China

Loess landslides induced by irrigation are common geological disasters in the Loess Plateau, China. Long-term watering decreases the matric suction and soil strength of loess, thus causing the frequent occurrence of landslides. Therefore, studying the strength characteristics of unsaturated loess is of great significance for knowing how such landslides occur and, a step further, preventing them. Undisturbed loess samples in Heifangtai Platform were collected to measure their soil water characteristic curves (SWCC) and a series of direct shear tests and triaxial shear tests were carried out with unsaturated loess. Moreover, the strength characteristics of the loess were discussed. The results showed that in the direct shear test, the cohesion (c) increased linearly with increasing matric suction whereas the suction internal friction angle (φb) was approximately constant. In the triaxial shear test, c increased nonlinearly with increasing matric suction. The value of φb was a constant when matric suction was 0–100 kPa, but decreased as matric suction increased within the range of 100–200 kPa. The effective stress parameter (χ) lay in the range from 0.5 to 0.8. When the matric suction was small, the shear strength calculated by Lu’s suction theory was almost the same as that obtained by Fredlund’s theory. With the increase of matric suction, the shear strength calculated by Fredlund’s theory gradually outperformed that of Lu’s suction theory. The shear strength calculated by the curve of moisture desorption was slightly larger than that of moisture absorption. The variation trends of strength parameters with matric suction under the two tests were similar. The effective internal friction angles obtained by the triaxial shear test are slightly larger than those by the direct shear test. The suction internal friction angle (φb) was approximately a constant and smaller than φ´. The φb obtained by the direct shear test was slightly larger than that obtained by the triaxial test. Lu’s theory can be used to evaluate the stability of unsaturated soils on some loess slopes with high soil moisture content.

Series resistance and interface states effects on the C–V and G/w–V characteristics in Au/(Co3O4-doped PVA)/n-Si structures at room temperature

Microwave-assisted method has been used for preparation of Co3O4 nanopowders. Then, Co3O4–doped polyvinyl alcohol (PVA) composites are deposited on n-Si wafer using spin coating method. The main electrical parameters of the Au/(Co3O4-doped PVA)/n-Si type Schotkky barrier diodes (SBDs) have been investigated by capacitance–voltage-frequency (C–V-f) and conductance–voltage-frequency (G/ω–V-f) measurements at room temperature and they were performed in the frequency range of 2 kHz–2 MHz and at (±4.5 V) by 50 mV steps. The XRD pattern of the as-prepared sample show that all diffraction peaks appeared in this pattern match very well with ICDD data and they can be readily indexed to the Co3O4 nanostructures, no other peaks were observed, which indicates the high purity of the sample. The effects of (Co3O4-doped PVA), series resistance (Rs) and surface states (Nss) on electrical characteristics have been investigated in detail. In order to eliminate the effect of Rs on high frequencies these measurements, the measured Cm and Gm/ω values were adjustment. The high values of Nss at low frequencies are responsible for the non-ideal behavior of C–V and G/ω–V characteristics. The obtained value of ND exponentially decreases; the value of ΦB (C–V) exponentially increases with increases frequency. Such behavior of ND and ΦB (C–V) are expected behavior and it is attributed to the particular density distribution of Nss, polarization processes and interfacial layer. Experimental results show that the C–V and G/ω–V characteristics of SBDs are affected not only in Nss and Rs but also interfacial polymer (Co3O4-doped PVA) layer.

Investigation of the C-V characteristics that provides linearity in a large reverse bias region and the effects of series resistance, surface states and interlayer in Au/n-Si/Ag diodes

The forward and reverse bias current-voltage (I-V), capacitance/conductance-voltage-frequency (C/G-V-f) characteristics of Au/n-Si/Ag Schottky barrier diodes (SBDs) were investigated by taking into account the effects of series resistance (Rs), surface states (Nss) and interlayer at room temperature. It is quite obvious that both C-V and G/ω-V plots showed reverse, depletion, and accumulation regions in a way that resemble those of good metal-insulator-semiconductor (MIS) type SBDs rather than those of MS type SBDs. The high value of ideality factor n = 1.907) was attributed to the existence of a native SiO2 interlayer, Nss and barrier inhomogeneity at M/S interface. The energy distribution profile of Nss was obtained from the forward bias I-V data by taking into account the voltage dependence of the effective barrier height (ΦB), n and Rs. The frequency dependent profiles of Nss and Rs were also obtained from C-V and G/ω-V data using Hill Colleman and Nicollian-Brews methods, respectively. The high values of C and G/ω at low frequency were attributed to the excess capacitance (Cex.) and conductance (Gex./ω) resulting from the Nss that could follow external ac signal. The value of ΦB obtained from the reverse bias C-V data for almost each frequency is higher than that of ΦB obtained from the forward bias I-V data. Such behavior of ΦB was attributed to the nature of measurement method. Experimental results confirmed that Nss and Rs are quite effective on the electrical characteristics in the existence of native or deposited interlayer.

Effect of Light Intensity and Temperature on the Current Voltage Characteristics of Al/SY/p-Si Organic–Inorganic Heterojunction

An organic–inorganic contact was fabricated by forming a thin film of sunset yellow dye (SY) on a p-Si wafer. The device showed a good rectification property, and the sunset yellow thin film modified the barrier height (Φb) of Al/p-Si contact by influencing the space charge region. The heterojunction had a strong response to the different illumination intensities and showed that it can be suitable for photodiode applications. The I–V measurements of the device were also applied in the temperature range of 100–500 K. It was seen that characteristic parameters of the device were strongly dependent upon temperature. While the value of Φb increased, the ideality factor (n) decreased with the increase in temperature. This variation was attributed to spatial inhomogeneity at the interface. The Norde function was used to determine the temperature-dependent series resistance and Φb values, and there was a good agreement with that of ln I–V data. The values of the Richardson constant (A*) and mean Φb were determined as 29.47 Acm−2 K−2 by means of a modified activation energy plot, matching with a theoretical one, and 1.032 eV, respectively. Therefore, it was stated that the current voltage characteristic with the temperature can be explained by thermionic emission theory with Gaussian distribution of the Φb at the interface.

The temperature dependent analysis of Au/TiO2 (rutile)/n-Si (MIS) SBDs using current–voltage–temperature (I–V–T) characteristics

In this study, the main electrical parameters of Au/TiO2(rutile)/n-Si Schottky barrier diodes (SBDs) were analyzed by using current–voltage–temperature (I–V–T) characteristics in the temperature range 200–380K. Titanium dioxide (TiO2) thin film was deposited on a polycrystalline n-type Silicon (Si) substrate using the DC magnetron sputtering system at 200°C. In order to improve the crystal quality deposited film was annealed at 900°C in air atmosphere for phase transition from amorphous to rutile phase. The barrier height (Φb) and ideality factor (n) were calculated from I–V characteristics. An increase in the value of Φb and a decrease in n with increasing temperature were observed. The values of Φb and n for Au/TiO2(rutile)/n-Si SBDs ranged from 0.57eV and 3.50 (at 200K) to 0.82eV and 1.90 (at 380K), respectively. In addition, series resistance (Rs) and Φb values of MIS SBDs were determined by using Cheung's and Norde's functions. Cheung's plots are obtained from the donward concave curvature region in the forward bias semi-logarithmic I–V curves originated from series resistance. Norde's function is easily used to obtain series resistance as a function of temperature due to current counduction mechanism which is dominated by thermionic emission (TE). The obtained results have been compared with each other and experimental results show that Rs values exhibit an unusual behavior that it increases with increasing temperature.

High permittivity, low dielectric loss, and high electrostatic potential barrier in Ca2Cu2Ti4O12 ceramics

Dielectric and nonlinear current–voltage properties of Ca2Cu2Ti4O12 (CaCu3Ti4O12/CaTiO3 composite) ceramics prepared by a simple thermal decomposition method were investigated. The results revealed that ceramics sintered at 1100°C for 12h exhibited a high dielectric constant (ε′~4.05×103) with temperature coefficient less than ±15% in the temperature range of −55–85°C, low loss tangent (tanδ~0.046) at 30°C and 1kHz, and high electronic potential barrier height (ΦB=0.856eV). These are desirable for applications based on the capacitive component. ε′ and ΦB increased significantly with increasing sintering time. tanδ was nearly constant. It suggests that a high value of ΦB is caused by the effect of CCTO–CTO interface.

Electrical properties of β-Ga2O3 single crystals grown by the Czochralski method

Electrical properties of nominally undoped β-Ga2O3 crystals grown by the Czochralski method from an iridium crucible under a carbon dioxide containing atmosphere were studied by temperature dependent conductivity and Hall effect measurements as well as deep level transient spectroscopy. All crystals were n-type with net donor concentrations between 6 × 1016 and 8 × 1017 cm−3. The Hall mobility of electrons was on average 130 cm2/Vs at room temperature and attained a maximum of 500 cm2/Vs at 100 K. The donor ionization energy was dependent on the donor concentration. Extrapolation of this dependence to zero concentration yielded a value of about 36 meV for isolated donors agreeing well with the ionization energy derived from effective-mass theory. Three deep electron traps were found at 0.55, 0.74, and 1.04 eV below the conduction bandedge. The trap at EC – 0.74 eV was detected in all samples with concentrations of 2 – 4 × 1016 cm−3. This concentration is comparable to that of compensating acceptors we have to take into account for an explanation of the temperature dependent electron density. Therefore, under the assumption that the electron trap at EC – 0.74 eV possesses acceptor character, this trap could be the dominating compensating acceptor in our crystals. Besides, a value of ΦB = (1.1 ± 0.1) V was determined for the Schottky barrier height of Ni on the (100) surface of n-type β-Ga2O3.

Reducing Schottky barrier height for Fe/n-GaAs junction by inserting thin GaOx layer

We investigated the effect of thin GaOx insertion layers on the Schottky barrier height ϕB for Fe/n-GaAs junctions. The value of ϕB showed a remarkable decrease from 0.84 down to 0.56 eV with increasing GaOx thickness up to 2.0 nm. Large suppression of ϕB is of greater advantage than using other oxide materials for achieving low contact resistance of the emitter/detector electrodes, which is the key to developing high-performance GaAs-based spintronics devices.

AlGaN/GaN two-dimensional electron gas Schottky barrier photodiodes with multiple MgxNy/GaN layers

In this study, AlGaN/GaN two-dimensional electron gas (2DEG) heterostructures were grown by metal organic chemical vapor deposition (MOCVD). It was found that we could reduce reverse leakage current and provide high-voltage operation by introducing multiple MgxNy/GaN layers into the conventional Schottky barrier photodiodes (SBPD). An atomic force microscopy (AFM) scan image showed that surface pits of TD terminations were hardly observed as the multiple MgxNy/GaN layers were grown before subsequently depositing a high-temperature (HT) AlGaN/GaN epitaxial layer. A larger Schottky barrier height (ΦB) and smaller ideality factor (n) extracted from the current–voltage (I–V) curve for SBPD with multiple MgxNy/GaN layers also suggested that better crystal quality and rectifying properties were achieved. The larger value of ΦB might be explained by the reduction of the TD density and interface state (IS) density.

High‐temperature stability of Au/p‐type diamond Schottky diode

AbstractRectification properties of Au Schottky diodes were investigated in high‐temperature operation. These diodes were fabricated on a p‐type diamond single crystal using the vacuum‐ultraviolet light/ozone treatment. The ideality factor n of the Schottky diodes decreased monotonically with increasing measurement temperature whereas the Schottky barrier height ϕb increased, and ϕb reached 2.6 eV at 550 K with n of 1.1. Through high temperature heating at 870 K, the mean value of ϕb at 300 K changed permanently from 2.2 eV to 1.1 eV. Decrease of ϕb might originate from a dissolution of oxygen termination at the Au/diamond interface. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

TH-D-210A-06: Drug Eluting Implanted Devices to Increase Biologic Effective Dose in Image Guided Radiation Therapy

Purpose:Image guided radiation therapy(IGRT), such as lungSBRT using fiducials or prostate brachytherapy, implant objects essitial to the radiation treatment, but offering no therapeutic benefit. Such devices offer a vechicle for in‐situ delivery of radiosensitizer which could increase the biologic effective dose of the radiation. This work studies the achievable drug coverage as a function of thechemical and physical properties of the drugs and devices. Method and Materials: Drug concentration around a spherical eluter is parameterized in order to separate the physical properties of the eluter and effective diffusion elimination modulus (φb) of the drug. Computer modeling is used to simulate drug distributions produced by configurations of eluters that could be encountered in either steretotactic body radiation therapy(SBRT) for lung or ultrasound guided prostate implants. Measures of tumor coverage and normal tissue involvement are evaluated for multiple combinations of eluter sizes and φb. Elution kinetics from polymercoating of gold substrate was evaluated. Results: A small number of fiducials, as in lungSBRT, would require either a relatively large fiducial or chemical engineering of the drug to produce a low value of φb. The many spacers seen in prostate brachytherapy provide enough eluters to sensitize a portion of the prostate with values of φb in the vicinity of reported values. The use of drug eluting brachytherapy spacers would enable a more localized enhancement in biologic effective dose than possible by a local brachytherapy boost. Timed release of docirubicin from a polymercoating on a gold substrate is possible. Conclusion:IGRT techniques already implant devices in targets as part of the standard of care. These devices may be enhanced with drug eluting coatings to provide localized increase in biologic effective dose without increasing the physical dose involved in the therapy.

Deformation of a Polymer Brush Immersed in a Binary Solvent

An analog of the Alexander-De Gennes box model is used for the theoretical investigation of an external deformation of polymer brushes in a mixture of two solvents. The basic solvent A and the admixture B are assumed to be highly incompatible (Flory-Huggins parameter χAB = 3.5). The thermodynamics of a polymer in the solvents A and B is described by parameters χA and χB, χA > χB. The brush behavior under deformation is investigated with regard to solvent composition and polymer-solvent interactions. It is shown that in a pre-binodal range of the solvent composition ΦB < ΦB0 in the bulk (here ΦB0 is a binodal value) there is such a value of ΦB = Φ B* that deformation does not affect solvent composition inside the brush. This invariant quantity Φ B*, being a function of only thermodynamic parameters, is independent of the brush characteristics, such as grafting density. It is shown that two types of the first-order phase transitions can arise in the system considered: a compositional phase transition induced by a change in the solvent composition in the bulk, and a deformational phase transition caused by an external deformation of the brush. The value of Φ B* defines a borderline concentration of the admixture in the bulk; the brush behavior in the ranges 00 ⪇ ΦB ⪇ Φ B* and Φ B* ⪇ ΦB < ΦB0 are different. If no compositional phase transition occurs in the system, the deformational phase transition should arise under stretching at Φ B* ⪇ ΦB. If the compositional phase transition exists, it is realized in the range ΦB < Φ B* and causes the deformational phase transition in this concentration range, not only under stretching, but also under compression. Microphase segregation inside the brush is demonstrated for both phase transitions despite overestimation of the brush homogeneity in the box model.

The effect of Ar+ ion implantation on the electrical characteristics of Cr/P-Si Schottky diodes

The effect of 150-keV Ar+ ion implantation of Cr/p-Si(100) Schottky contacts was studied by measuring the current voltage characteristics over the temperature range 293–373 K before and after different doses of ion bombardment. The characteristics obtained were used in a least-squares fitting procedure to determine the ideality constant n, the saturation current IS, the series resistance R, and the Schottky barrier height Φb. Ar+ ion bombardment resulted in higher values for n and R but a lower value for IS. The value of Φb increased by 10%. The apparent reason for the increase in Φb for p-type contacts as well as the decrease for n-type contacts is discussed in reference to the identical behavior earlier reported for low-energy inert gas ion beam etching and reactive ion etching of Si.

Effects of tunneling on a-Si:H Schottky barriers

Schottky diodes have been prepared by depositing semitransparent metallic films (Pd, Cr, and Au) onto hydrogenated amorphous silicon (a-Si:H) grown by the glow-discharge method. The a-Si:H was n doped and undoped presenting different densities of gap states (Ns). Barrier heights Φb were measured by internal photoemission and correlated to Ns. The activation energies were also determined. The results are understood in terms of both thermionic-field-emission tunneling and resonant tunneling through localized states of the conduction-band tail. It is found that the latter tunneling effect has a remarkable influence on the experimentally determined value of Φb.

Temperature and field dependence of intergrain barriers in polycrystalline n-InSb films

Field-effect Hall mobility studies were made on polycrystalline n-type InSb films. The intergrain barrier potential is found to be dependent on both temperature and applied gate field. The experimental results fit well with an intergrain barrier potential of the form φb = φ0(1+αT)(1+αq+bq2), where φ0 is the value of φb at zero gate field and absolute zero temperature, α is the temperature coefficient of φb, and a and b are constants.

研削焼けの発生からみたクリープフィード研削条件の選択

This paper aims to clarify the condition under which workpiece burning occurs in creep feed grind-ing and by connecting the result to obtain an optimal grinding condition which can avoid any occurrence of burning. With continuing operation, the grinding wheel becomes dull and workpiece burning takes place when the grinding energy flux φ (grinding energy per unit contact area per unit time) exceeds a critical value of φb. According to the experiment, the value of, was about 7-8 J/mm2·s and was not influenced by the wheel, the grinding manner nor the contact length of wheel and workpiece, but was solely a function of dimen-sionless grain depth of cut hg=- (Vw/Vs) a/D. The φ value increases from an initial φ0 almost linearly with the path length of grain L. Therefore the φb as well as the rate of increase of φ with L must be as small as possible in order to avoid workpiece burning. Taking all the above factors into consid-eration, nomographs to indicate the optimal grind-ing conditions in view of burning are presented.

Surface State and Interface Effects on the Capacitance-Voltage Relationship in Schottky Barriers

In the presence of an interfacial layer and semiconductor surface states, a Schottky barrier height φb decreases with increasing electric field E at the surface of the semiconductor. If the semiconductor doping concentration Nd is uniform throughout the depletion region and if [ (qNd/ε) (dφb/dE)−E] [ (d2φb/dE2) (dE/dV) ]≪1,where V is the applied voltage and ε is the semiconductor permittivity, the slope of the (capacitance)−2 vs voltage relationship is constant and can be interpreted to give Nd. The voltage intercept of the relationship yields an apparent barrier height φa related to the true barrier φb by φa=φb−E (dφb/dE) + (qNd/2ε) (dφb/dE)2, where q is the electron charge. From the measured variation of φa with Nd and one absolute measure of φb at one value of Nd, φb(E), and dφb(E)/dE may be deduced. From dφb(E)/dE the surface state density as a function of energy in the bandgap and the minimum value of interface thickness divided by relative interface permittivity can be obtained. Using the data of Archer and Atalla for vacuum cleaved Au-Si diodes to illustrate our method, the surface state density is found to peak at a value of ∼2×1014 cm−2·eV−1 at about 0.83 below the conduction band and the minimum value of interface thickness divided by relative dielectric constant is found to be of the order of 5 Å. Criteria are given which show how Schottky diode capacitance-voltage data may be further used, in conjunction with photoelectric barrier measurements, to detect the presence of deep lying impurities or the penetration of surface state charge into the body of the semiconductor.