Depth profiles of the majority carrier concentration and the minority carrier effective lifetime in gettered GaAs

The first results are reported on the concentration profiles of majority carriers and the effective lifetime profiles of minority carriers in thick (1.6 mm) GaAs plates subjected to surface gettering. It was established that the one-and two-sided coating of the GaAs plates with Y films, followed by heat treatment at 700–800°C, allows a high-resistivity material to be obtained with homogeneous distributions of the electron concentration and the hole lifetime in depth of the semiconductor.     

Analysing the risk of LNG carrier operations

This paper presents a generic, high-level risk assessment of the global operation of ocean-going liquefied natural gas (LNG) carriers. The analysis collects and combines information from several sources such as an initial hazid, a thorough review of historic LNG accidents, review of previous studies, published damage statistics and expert judgement, and develops modular risk models for critical accident scenarios. In accordance with these risk models, available information from different sources has been structured in the form of event trees for different generic accident categories. In this way, high-risk areas pertaining to LNG shipping operations have been identified. The major contributions to the risk associated with LNG shipping are found to stem from five generic accident categories, i.e. collision, grounding, contact, fire and explosion, and events occurring while loading or unloading LNG at the terminal. Of these, collision risk was found to be the highest. According to the risk analysis presented in this paper, both the individual and the societal risk level associated with LNG carrier operations lie within the As Low As Reasonable Practicable (ALARP) area, meaning that further risk reduction should be required only if available cost-effective risk control options could be identified. This paper also includes a critical review of the various components of the risk models and hence identifies areas of improvements and suggests topics for further research.     

Time transfer using the phase of the GPS carrier

We report on tests of time transfer using the phase of the GPS carrier. The first set of experiments used two clocks connected to independent GPS receivers with closely-spaced antennas. The second set of experiments compared a clock at NIST in Boulder with one at the US Naval Observatory in Washington, DC.     

中国瓦良格航母使用尖端技术

航母建设牵涉到机械制造、结构设计、航天、通信、预警、信息处理等诸多领域的关键技术,发展航母,这些,都是绕不过去、必须解决的难题,中国改造"瓦格良"号航母,走的就是一条改造积累经验、自行制造成型的稳妥的道路,而在这过程中,相关领域的技术创新,相信也会如中国"两弹一星"成功,支撑起一个航天大国一样,起到积极的     

On the determination of carrier mobility in compensated GaAs

The applicability of the Brooks-Herring and Conwell-Weisskopf formulas in calculations of the carrier mobility associated with scattering by ionized impurities is examined usingn-type GaAs as an example. The Brooks-Herring approximation is shown to be inapplicable at large compensation ratios, where the Conwell-Weisskopf formula is more accurate. The applicability limits of the two formulas are established for calculations of carrier mobility from dopant concentration and compensation ratio and for calculations of the concentration of ionized centers (compensation ratio) from carrier concentration and mobility. The predicted applicability limits are consistent with experimental data.     

The problem of monitoring the leakage of a heat carrier

In the approximation of slight inhomogeneity of a dielectric, the capacitance of a capacitor is determined. For a gas model, when the inhomogeneity of the dielectric results from the diffusion of an impurity into the interelectrode gap, the dynamics of the change in the capacitance and the current in a chain is studied as a function of the geometric parameters of the capacitor and the electrophysical properties of the impurity.     

Effect of carrier concentration on the microhardness of GaN layers

The paper presents a microhardness study of thick crack-free hydride vapor phase epitaxial GaN layers (not intentionally doped), and of thin metal-organic vapor phase epitaxial (MOVPE) GaN layers (undoped and Si-doped), grown on sapphire. A Vickers indentation method was used to determine the microhardness under applied loads up to 2 N. An increase in the microhardness was observed with decreasing carrier concentration and increasing mobility. A dip at an indentation depth of about 0.75 μm is observed in the microhardness profile in the MOVPE films, and is correlated with peculiarities in the spatially resolved cathodoluminescence spectra. The relationship between the mechanical and electrophysical parameters is discussed.     

Measuring the carrier frequency of radio-frequency signals by the comparison method

Translated from Izmeritel'naya Tekhnika, No. 8, pp. 43–44, August, 1991.     

多孔镍载体材料的制备

试验在常规粉末冶金方法基础上通过添加造孔剂的办法制备出高孔率(70%以上)、小孔径(最大冒泡孔径＜5 μ m)、高透过量,通孔率(通孔率可达97%以上)的多孔镍载体材料.主要进行了粉末粒度及形貌的分析选择研究,造孔剂的添加量与多孔镍载体性能关系的研究、烧结工艺对材料性能影响的研究.主要从孔率、最大冒泡孔径、透气系数、通孔率等方面着手,研究了造孔剂加入量及烧结工艺对该性能的影响,同时对不同条件下样品的性能进行了测试.     

Effects of strain on the carrier mobility in silicon nanowires

We investigate electron and hole mobilities in strained silicon nanowires (Si NWs) within an atomistic tight-binding framework. We show that the carrier mobilities in Si NWs are very responsive to strain and can be enhanced or reduced by a factor >2 (up to 5×) for moderate strains in the ± 2% range. The effects of strain on the transport properties are, however, very dependent on the orientation of the nanowires. Stretched 100 Si NWs are found to be the best compromise for the transport of both electrons and holes in ≈10 nm diameter Si NWs. Our results demonstrate that strain engineering can be used as a very efficient booster for NW technologies and that due care must be given to process-induced strains in NW devices to achieve reproducible performances.     

Structural effects on the carrier mobility of organic field-effect transistors

This work examined pentacene organic field-effect transistors built on polycrystalline, single-grain, and single-crystal thin films. Mobility data obtained in the literature were matched to equations developed from charge hopping and the Gaussian disordered model. Our results indicated that it was possible to harmonize conventional dispersive charge transport with the hopping process. Assuming that charge conduction between trap states in the inter-granular region was barrier-height limited and affected by the gate voltage, we were able to estimate the material parameters appearing in our model equations. Our results indicated that very different values of the rms widths of the density of (transport) states existed in the different thin films.     

Contactless probing of the intrinsic carrier transport single-walled carbon nanotubes

Intrinsic carrier transport properties of single-walled carbon nanotubes have been probed by two parallel methods on the same individual tubes： The contactless dielectric force microscopy （DFM） technique and the conventional field-effect transistor （FET） method. The dielectric responses of SWNTs are strongly correlated with electronic transport of the corresponding FETs. The DC bias voltage in DFM plays a role analogous to the gate voltage in FET. A microscopic model based on the general continuity equation and numerical simulation is built to reveal the link between intrinsic properties such as carrier concentration and mobility and the macroscopic observable, i.e. dielectric responses, in DFM experiments. Local transport barriers in nanotubes, which influence the device transport behaviors, are also detected with nanometer scale resolution.     

Stabilizing the optimal carrier concentration for high thermoelectric efficiency

The band structure of PbTe can be manipulated by alloying with MgTe to control the band degeneracy. This is used to stabilize the optimal carrier concentration, making it less temperature dependent, demonstrating a new strategy to improve overall thermoelectric efficiency over a broad temperature range.