Low Compensation Ratio Research Articles

Effect of annealing time and pressure on electrical activation and surface morphology of Mg-implanted GaN annealed at 1300 °C in ultra-high-pressure nitrogen ambient

We performed an isothermal annealing study on Mg-implanted GaN at 1300 °C in an ultra-high-pressure (1 GPa) nitrogen ambient. Annealing for more than 30 min resulted in a high acceptor activation ratio and a low compensation ratio that were comparable to those obtained with annealing at 1400 °C for 5 min. We also performed annealing at 1300 °C in a reduced nitrogen pressure of 300 MPa which makes us possible to expand the inner diameter of annealing equipment in the future. High electrical activation, similar to one obtained by annealing at 1 GPa, was successfully obtained.

An on-demand service platform with self-scheduling capacity: Uniform versus multiplier-based pricing

On-demand service platforms use multiplier-based pricing to provide services via self-scheduling participants. In a multiplier-based pricing scheme, consumers pay lower prices during non-peak periods and higher prices equal to the non-peak period price multiplied by a surge multiplier during peak periods. However, the reasons underlying multiplier-based pricing and when it should be used remain unclear. In this paper, we examine the effects of two pricing schemes—uniform pricing and multiplier-based pricing—on platform profits, participant payoff, and consumer surplus by formulating game-based models, and investigate the conditions and feasible region for use of multiplier-based pricing. The results show that the non-peak price in the multiplier-based pricing scheme is lower than the uniform price, which is in line with reality. When the number of potential participants in non-peak periods is larger, the multiplier-based pricing model generates more profits if compensation ratios in the two models are higher or the compensation ratio in the multiplier-based pricing model is lower. Participants are better off joining a platform that uses uniform pricing given one of the following conditions: lower commission ratio in the two models, lower compensation ratio in the multiplier-based pricing model and higher commission ratio in the two models, and higher commission and compensation ratios in the two models. Consumers are better off in the uniform pricing model if the proportion of non-peak periods, consumer sensitivity to surge multiplier change, and the ratio of potential participants in peak and non-peak periods are higher.

A quantitative liability risk assessment of oil spills in oil ports: the case of the Guangdong-Hong Kong-Macao Greater Bay Area

ABSTRACT To mitigate risk and enhance safety in oil ports, this study proposes a method to analyse the civil liability risk and criminal liability risk of oil spills in oil ports. Based on scenario analysis and data analysis, the probability, spill size, number of casualties, actual compensation and total spill cost are estimated for different scenarios, including loading arm/hose rupture and hull failure when a vessel is berthing, manoeuvring near a berth and moving through the port. Based on these estimated factors and legal liability, the civil liability risk and criminal liability risk borne by oil ports and ship owners are estimated. Finally, data from an oil terminal in the Guangdong-Hong Kong-Macao Greater Bay Area are used to verify the applicability of the proposed method. The estimated probability and corresponding consequences can be used to determine which scenario would result in criminal liability and provide a reference for emergency capacity planning. The estimated risks are useful for loss mitigation and crime prevention. The findings and analysis reveal the current low compensation ratio and the inconsistency in criminal standards for oil spills in China. Therefore, the enforcement of civil compensation and unity among criminal standards should be prioritized.

Extremely high-efficient activation of acceptor boron introduced by ion implantation at room temperature with various doping concentrations in epitaxially synthesized diamond films by chemical vapor deposition

We homoepitaxially synthesized a pure diamond film on type Ib base substrates by microwave plasma-assisted special chemical vapor deposition method and then doped B impurity atoms by the ion implantation technique with various doping concentrations from 2×1017 to 2×1019 cm−3 at room temperature followed by activation annealing at 1300 °C. The electrical properties of specific resistance, carrier concentration, Hall mobility, and conductive carrier type were analyzed by Hall effect measurements based on the van der Pauw method at sample temperatures from 77 to 873 K. We consequently realized excellent B-doping in the CVD-synthesized diamond film with a low compensation ratio and perfect doping efficiency and confirmed p-type conduction at almost all temperature ranges for the measured samples. In very lightly doped diamond, we observed first the existence of deep acceptor levels located near 1.85 eV with respect to the valence band maximum and proposed a conduction mechanism based on hopping conduction in deep acceptor levels. We showed the availability of this doping process to high-efficient B doping with various acceptor concentrations in diamond. The great success achieved in the activation of acceptor B implanted in diamond with various doping concentrations should definitely contribute to the progress in the application of diamond-based power semiconductor devices.

Optical characteristics of highly conductive n-type GaN prepared by pulsed sputtering deposition

We have characterized highly conductive Si-doped GaN films with a high electron mobility of 112 cm2V−1s−1 at an electron concentration of 2.9 × 1020 cm−3, prepared using pulsed sputtering deposition (PSD). With an increase in the doping concentration, the absorption edge was found to shift toward a higher energy level, owing to the Burstein-Moss effect, thus making this material suitable for the transparent conductive tunneling electrodes of visible and ultraviolet-A light-emitting diodes. The full width at half maximum value of the near-band-edge (NBE) emissions in a photoluminescence spectrum measured at 77 K was as small as 185 meV, even for the sample with the highest electron concentration of 2.9 × 1020 cm−3. Such sharp NBE emissions from PSD-grown heavily Si-doped GaN films can be explained by an analytical model with a low compensation ratio θ of around 0.1, which is consistent with the exceptionally high observed electron mobility. These results indicate the strong potential of the low-temperature PSD growth technique for the formation of high-quality, heavily Si-doped GaN.

Hole Transport in Arsenic-Doped Hg1−x Cd x Te with x ≥ 0.5

Hole transport in arsenic-doped p-type Hg1-xCdxTe epitaxial layers with x ≥ 0.5 has been studied employing Hall-effect measurements and theoretical modeling of hole scattering mechanisms. The hole transport parameters extracted from four different Hg1-xCdxTe films with x = 0.50, 0.56–0.58, 0.65, and 0.80, were analyzed using an iterative solution of Boltzmann’s transport equation. Hole mobilities in the samples with x values of 0.5 and 0.56–0.58 were found to be predominantly limited by ionized impurity scattering, and exhibited relatively high impurity compensation ratios ≥2. The sample with x = 0.65 exhibited the highest hole mobility, a low compensation ratio of 1.05, and mobility characteristics were limited predominantly by polar optical phonon scattering at temperatures ≥200 K. Hole mobility in the sample with x = 0.80 was found to be limited by polar optical phonon scattering and ionized impurity scattering (compensation ratio 1.20–1.56). Although the sample temperatures employed were not sufficiently low to unambiguously discriminate the scattering strength of static strain and dislocations, the experimental hole mobility characteristics cannot be adequately modeled if these two mechanisms are neglected. The ionization energy of the arsenic acceptor impurities was found to exhibit a quadratic dependence on the CdTe mole fraction.

Hall-effect measurements of metalorganic vapor-phase epitaxy-grown p-type homoepitaxial GaN layers with various Mg concentrations

Mg-doped p-type gallium nitride (GaN) layers with doping concentrations in the range from 6.5 × 1016 cm−3 (lightly doped) to 3.8 × 1019 cm−3 (heavily doped) were investigated by Hall-effect measurement for the analysis of hole concentration and mobility. p-GaN was homoepitaxially grown on a GaN free-standing substrate by metalorganic vapor-phase epitaxy. The threading dislocation density of the p-GaN was 4 × 106 cm−2 measured by cathodoluminescence mapping. Hall-effect measurements of p-GaN were carried out at a temperature in the range from 160 to 450 K. A low compensation ratio of less than 1% was revealed. We also obtained the depth of the Mg acceptor level of 235 meV considering the lowering effect by the Coulomb potential of ionized acceptors. The hole mobilities of 33 cm2 V−1 s−1 at 300 K and 72 cm2 V−1 s−1 at 200 K were observed in lightly doped p-GaN.

Low resistivity and low compensation ratio Ga-doped ZnO films grown by plasma-assisted molecular beam epitaxy

In this study, Ga-doped ZnO (GZO) thin films were deposited on GaN templates by using plasma-assisted molecular beam epitaxy. To obtain low resistivity GZO films, in-situ post-annealing under Zn overpressure was carried out to avoid the generation of acceptor-liked Zn vacancies. The resultant films showed optical transparency over 95% in the visible spectral range. By reducing the acceptor-like defects, GZO films with compensation ratio near 0.4 and resistivity simultaneously lower than 1×10−4Ωcm have been successfully demonstrated.

Temperature‐dependent Hall‐effect measurements of p‐type multicrystalline compensated solar grade silicon

ABSTRACTIn this study, we have investigated the Hall majority carrier mobility of p‐type, compensated multicrystalline solar grade silicon (SoG‐Si) wafers for solar cells in the temperature range 70–373 K. At low temperature (~70 K) the difference in the mobilities measured for the compensated and the uncompensated reference samples is the highest, and the measured mobility shows dependence on the compensation ratio. Mobilities decrease with increasing temperature, and towards room temperature, the mobilities of the different samples are in the same range. The measurements show that, for these samples, the contribution from lattice scattering is dominating over ionized impurity scattering at room temperature. In the range of interest for silicon solar cells (above room temperature), the trend in carrier mobility is similar for all the samples, and the measured value for the sample with low compensation ratio and low doping density is comparable to the uncompensated references. A comparison of resistivity and majority carrier density measured by the Hall setup at room temperature and by four‐point probe and glow discharge mass spectroscopy, respectively, is reported as well. Copyright © 2012 John Wiley & Sons, Ltd.

Foreign Institutional Investors and Corporate Governance in Emerging Markets: Evidence from Split Share Reform in China

We study the benefits of opening up local equity markets to foreign institutional investors using data on Qualified Foreign Institutional Investors (QFIIs) in China around the reform floating non-tradable shares. We find evidence supporting the view (Stulz (1999)) that as “outsiders,” foreign institutional investors are less prone to political pressure and are more likely to perform arm’s length monitoring than local mutual funds. In particular, the presence of QFII ownership shortens the duration of reform, enhances the terms in negotiation, and increases the compensation to tradable shareholders. We confirm that while state-controlled companies on average offer higher compensation ratio for a quicker approval, the state entities may exert political power and offer lower compensation ratio for companies with domestic mutual fund ownership (Firth et al (2008)). In contrast, we further find that the positive relation between state ownership and the final compensation ratio increases with the level of QFII ownership. QFIIs increase the likelihood of change in the compensation proposal among state-controlled companies, while local mutual funds show opposite effect. These results are unlikely due to endogeneity problem as local mutual funds and QFII have closely akin portfolio holdings and similarly positive effect on firm value. Our study suggests that the influx of large foreign institutional investors help promote market principle in corporate governance in emerging markets and alleviate the “twin agency” problem from state ruler discretion. (Stulz (2005))

Properties of Si-doped GaN and AlGaN/GaN heterostructures grown by RF-MBE on high resistivity Fe-doped GaN

Abstract Silicon-doped GaN epilayers and AlGaN/GaN heterostructures were developed by nitrogen plasma-assisted molecular beam epitaxy on high resistivity iron-doped GaN (0001) templates and their properties were investigated by atomic force microscopy, x-ray diffraction and Hall effect measurements. In the case of high electron mobility transistors heterostructures, the AlN mole fraction and the thickness of the AlGaN barrier employed were in the range of from 0.17 to 0.36 and from 7.5 to 30 nm, respectively. All structures were capped with a 2 nm GaN layer. Despite the absence of Ga droplets formation on the surface, growth of both GaN and AlGaN by RF-MBE on the GaN (0001) surfaces followed a step-flow growth mode resulting in low surface roughness and very abrupt heterointerfaces, as revealed by XRD. Reciprocal space maps around the ( 10 1 5 ) reciprocal space point reveal that the AlGaN barriers are fully coherent with the GaN layer. GaN layers, n -doped with silicon in the range from 1015 to 1019 cm−3 exhibited state of the art electrical properties, consistent with a low unintentional background doping level and low compensation ratio. The carrier concentration versus silicon cell temperatures followed an Arhenius behaviour in the whole investigated doping range. The degenerate 2DEG, at the AlGaN/GaN heteroiterfaces, exhibited high Hall mobilities reaching 1860 cm2/V s at 300 K and 10 220 cm2/V s at 77 K for a sheet carrier density of 9.6E12 cm−2. The two dimensional degenerate electron gas concentration in the GaN capped AlGaN/GaN structures was also calculated by self-consistent solving the Schrodinger–Poisson equations. Comparison with the experimental measured values reveals a Fermi level pinning of the GaN (0001) surface at about 0.8 eV below the GaN conduction band.

Hydrogen-plasma assisted molecular beam epitaxial growth of high-purity InAs

In this article we report the effect of H plasma on the purity and transport properties of molecular beam epitaxial (MBE) grown InAs, which has attracted considerable attention for high-speed and low power electronic devices in recent years. We observed that the native oxide on the InAs surface could be desorbed at temperatures as low as 300°C under H-plasma irradiation. The time required for oxide desorption increased with decreasing substrate temperature. Thick InAs was grown with H-plasma assistance on semi-insulating (SI) GaAs and on an AlAs0.16Sb0.84∕InAs insulating buffer layer to investigate the effect of H plasma on the transport properties of InAs. Significant improvement of the electron mobility was observed using H-plasma assisted growth. For 6μm InAs grown with H plasma on SI GaAs, the electron mobilities were as high as 98000cm2∕Vs at 77K and 19500cm2∕Vs at 300K, which represent the best published data for MBE grown InAs on GaAs. For thick InAs grown on AlAs0.16Sb0.84∕InAs, the electron mobilities were as high as 420000cm2∕Vs at 77K and 31000cm2∕Vs at 300K. The free carrier concentration of InAs grown with H-plasma assistance is larger than that of the sample grown without, indicating the H plasma yields a much lower compensation ratio γ(γ=(NA+ND)∕n), and moreover, the H plasma is more effective in passivating acceptors than donors in InAs. The mobility and free carrier concentration were both unchanged after thermal annealing, which are advantageous for device processing.

Zinc doped GaAs epitaxial layers MOVPE grown by liquid metalorganic sources

AbstractThe properties of Zinc‐doped GaAs, grown by MOVPE employing the tertiary buthyl arsine precursor, were studied as a function of the doping level, comprised within the (1 × 1016 – 7 × 1019 cm–3) range. Hall effect measurements were performed as a function of temperature; the simultaneous analysis of the Hall hole density and Hall mobility gave the effective doping concentration, the thermal ionisation energy of the acceptor impurities and the compensation ratio. Fast Fourier Transform Photoluminescence measurements were performed on the GaAs layers; the results were correlated with those obtained from the electrical analysis. A comparison of the obtained data with the results of an analogous investigation, previously performed on intrinsically Carbon doped GaAs layers, allowed the following conclusions: a) the GaAs layers exhibit a low content of non‐intentional impurities (<1014 cm–3); b) both Zinc and Carbon show a low compensation ratio; c) both Carbon and Zinc doped layers show electrical and optical properties comparable with the state of the art; d) Carbon intrinsic doping appears preferable for low‐medium carrier concentrations, while Zinc appears preferable for medium‐high carrier concentrations (higher than about 5 × 1017 cm–3). (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Device Grade B-Doped Homoepitaxial Diamond Thin Films

We review our recent results on properties of high quality B-doped homoepitaxial diamond thin films grown by chemical vapor deposition (CVD) by using trimethylboron (TMB) as a B source gas. The conventional (one-step) and the two-step growth methods were used for film preparation. The latter realized smooth surface without any non-epitaxial crystallites (UCs). The films showed a sharp Raman shift peak at 1332 cm -1 , a strong free-excitonic emission at room temperature, and high Hall mobility as high as 1000 cm 2 /Vs or more, indicating high-quality diamond. We also successfully realized resistivity control of the films in a wide range from 10 0 to 10 5 Ω cm due to low compensation ratio. Using the two-step growth method, Schottky junctions with the ideality factor n of 1.1 or less and undetectable leakage current could be prepared between various metals such as Al, Zn, Cr, Ni, Au or Pt and oxidized B-doped CVD diamond films. In particular, we successfully made nearly ideal Schottky junctions using highly B-doped films in the order of 10 17 cm -3 , indicating that the quality of the present B-doped films is comparable with or higher than those of conventional semiconductors such as Si and GaAs.

Hall mobility and carrier concentration in free-standing high quality GaN templates grown by hydride vapor phase epitaxy

Measured and calculated (without any adjustable material parameter) electron Hall mobility and carrier concentration in the range of 26.5–273 K are reported for a high-mobility free-standing bulk GaN grown by hydride vapor phase epitaxy. The peak electron mobility of 7386 cm 2/V s at 48 K and a value of 1425 cm 2/V s at 273 K were measured. An iterative solution of the Boltzmann equation was applied to calculate the mobility using the materials parameters either measured on the sample under study or recent values that are just becoming available with only the acceptor concentration being variable. Using only one donor and one conducting layer system, the donor and acceptor concentrations of 1.76×10 16 and 2.4×10 15 cm −3, respectively, satisfy simultaneously the charge neutrality and electron mobility at all temperatures within the framework of the iterative method and measurements. The donor activation energy was determined to be 25.2 meV and is consistent with the value of about 30 meV for the hydrogenic ground state in a dilute semiconductor. The high electron mobility, low background impurity concentration, low compensation ratio, and negligible dislocation scattering demonstrate the high quality of the material studied.

MeV Ion Implantation Doping of Diamond.

AbstractDiamond-based semiconductor devices offer the promise of operation at high temperatures and under extreme radiation conditions. An essential step in the drive towards operational diamond-based electronic devices is the ability to controllably and reproducibly dope the diamond. Ion implantation is the method of choice for such doping because it offers precise control of the dopant concentration and spatially selective doping is achievable using standard masking techniques. However, compared to silicon, the doping of diamond is complicated by the tendency of the diamond to relax to graphite upon thermal annealing. Furthermore, even if graphitization can be avoided, the compensation of dopants by residual defects has proved in the past to be a limiting factor in obtaining very high mobility material. In this paper, we present a scheme for the effective doping of diamond using MeV ion-implantation. For MeV ion- implantation the doped layer is deeply buried under a cap of undamaged diamond, and so the scheme includes a method using pulsed laser irradiation for making electrical contact to the buried layer. We show that a boron doped layer fabricated by the MeV implantation scheme has, after suitable annealing and removal of these compensating/trapping defects, very high mobility and low compensation ratio. In fact, its electrical properties are quite similar to those of natural boron-doped type IIb diamond.

A large range of boron doping with low compensation ratio for homoepitaxial diamond films

A large range ([B] from 5×10 16 to 8×10 20 cm −3) of boron concentration has been obtained for homoepitaxial diamond films. From the variation of the conductivity versus temperature between 300 and 1000 K, a simpler method is used to derive the activation energy(ies) E a and the compensation ratio than from the variation of the hole concentration and mobility with temperature. For [B]<2×10 17 cm −3, a saturation of the conductivity is observed between 680 and 1000 K, E a= E i (ionisation energy of the boron), and compensation ratio around 10% is deduced. Then, up to 10 19 cm −3, an additional E a= E i/2=185 meV is observed between 500 and 1000 K, with compensation ratio <10%. At higher [B], an additional nearest neighbour hopping contribution to the conduction is obtained from the formation of the boron impurity band. It dominates and gives metallic conductivity when [B]=3×10 20 cm −3.

High Quality InP Epitaxial Growth Using Flow Rate Modulation Metalorganic Chemical Vapor Deposition

The characteristics of modified flow rate modulation metalorganic chemical deposition is studied. From observation with the atomic force microscope, the flatness of a InP homoepitaxial layer is improved to atomic scale by phosphine modulation metalorganic chemical vapor deposition. The full width at half maximum 5.6 meV of photoluminescence at 77 K can be achieved under optimum growth conditions. The satellite peak around the near band emission can also be reduced to a negligible quantity under optimum growth conditions. Also, MFME can improve the electrical characteristics of the epilayer with higher electron mobility and lower compensation ratio.

Transport properties in gallium doped CdTe MOVPE layers

Hall measurements have been performed on gallium-doped n-type CdTe metalorganic vapor phase epitaxy layers between 25 and 300 K. The Hall coefficient and mobility data could be better explained assuming a singly ionized donor model. The ionization energy of the isolated shallow donor is estimated to be about 15.3 meV below the conduction band. The analysis also showed that the layers are not heavily compensated. Low-temperature mobilities as high as 3000 cm 2/V · s are obtained. The model of scattering by optical phonon, acoustical phonon, ionized and neutral impurity satisfactorily accounts for the mobility data, supporting the low compensation ratio obtained from the carrier concentration analysis. The results demonstrate that high-quality n-type layers can be obtained using gallium.

Silicon doping of InP using modified flow rate modulation epitaxy

In this study, silicon doping using flow rate modulation epitaxy was found to produce better characteristics compared with conventional metal-organic chemical vapor deposition of the same growth system. The amount of phosphine is very critical in this new growth method. A lower compensation ratio (0.1) and higher mobility (3200 cm 2 V −1 s −1 at 300 K) are obtained under the optimum conditions. These are very important for application to high speed and low noise devices.