摘要:

Hole transport in bulk silicon is explored using an efficient and accurate Monte Carlo (MC) tool based on the local pseudopotential band structure. Acoustic and optical phonon scattering, ionized impurity scattering, and impact ionization are the dominant scattering mechanisms that have been included. In the interest of computational efficiency, momentum relaxation times have been used to describe ionized impurity scattering and self-scattering rates have been computed in a dynamic fashion. The temperature and doping dependence of low-field hole mobility is obtained and good agreement with experimental data has been observed. MC extracted impact ionization coefficients are also shown to agree well with published experimental data. Momentum and energy relaxation times are obtained as a function of the average hole energy for use in moment based hydrodynamic simulators. The MC model is suitable for studying both low-field and high-field hole transport in silicon. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.364287

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

From free-carrier absorption measurements of spatially and temporally resolved excess carrier concentrations in the n-base of electron irradiated, low doped, highly injectedp-i-ntype diodes, the effective ambipolar lifetime has been extracted with respect to different injection levels and temperatures. By measuring lifetimes up to injection levels of3×1017cm−3, the ambipolar Auger coefficientCaand its temperature dependence has been determined in the range of 300–420 K. In accordance with recent publications, the room temperature value of the Auger coefficient was found to be about three times higher than one of the most commonly used values. Further on, the ambipolar Auger coefficient is empirically estimated to vary with temperature asCa(T)=1.1×10−30(T/300)1.8, wereTis the absolute temperature. Also the ambipolar diffusion coefficient has been investigated and compared with different models. The results are important and useful in simulation of high-injected silicon devices, i.e., solar cells and power devices. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.364277

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Thermal conductivity in nickel solid solutions with a &ggr; single phase was comprehensively surveyed. The major findings are summarized as follows: First, alloying definitely decreases the thermal conductivity of nickel. The relationship between thermal conductivity and concentration in the dilute solid solution is characterized by the Nordheim relation. Second, for most solutes, the thermal conductivity of nickel alloys decreases significantly as the position of the solute element becomes horizontally more distant from nickel in the periodic table, which is equivalent to the Norbury–Linde rule of electrical resistivity. Third, cold deformation has no significant influence on the thermal conductivity of nickel alloys. Fourth, a monotonic increase in thermal conductivity as a function of temperature is observed in highly concentrated nickel alloys, while the thermal conductivity of dilute nickel alloys shows a minimum at the Curie temperature. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.364254

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We have carried out a coordinated experimental and theoretical study of single-electron traps based on submicron metallic (aluminum) islands and Al/AlOx/Al tunnel junctions. The results of geometrical modeling using a modified version of MIT’sFASTCAPwere used as input data for the general-purpose single-electron circuit simulatorMOSES. The analysis indicates reasonable quantitative agreement between theory and experiment for those trap characteristics which are not affected by random offset charges. The observed differences (ranging from a few to fifty percent) can be readily explained by the uncertainty in the exact geometry of the experimental nanostructures. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.364278

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The impact of grain size on the average collection probability of fine grained (<10 &mgr;m) polycrystalline silicon has been investigated using a numerical device simulator. This model predicts that the collection probability can improve dramatically once the depletion regions around adjacent grain boundaries overlap. Thus, contrary to most analytical models, the collection probability is not monotonic with grain size. The collection probability has a local maximum at a grain size determined by the grain boundary trap state density. The magnitude of the improvement is dependent upon the grain boundary recombination velocity. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.364279

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We present an observation of extensive space-charge limited conduction in polybenzo[c]thiophene. Strong evidence for the presence of three discrete trapping levels is shown with a possibility of a fourth trap level. The density of traps for the first three levels is found to be 5×1016cm−3, 1×1017cm−3, and 2×1017cm−3, respectively. A lower limit for the free-carrier mobility was estimated to be ∼3×10−5cm2 V−1 s−1. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.364280

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We have searched for superconductivity in a wide variety of stoichiometries in the Y-Ni-B-C system, usingYx(NiB)Cyphase spread alloy thin films and the magnetic field modulated microwave absorption technique. The superconducting critical temperature(Tc)varies with the stoichiometry, showing the highestTcfor a Y/Ni ratio of 1/2, attributed to theYNi2B2Cphase. We found no other superconducting phases with aTchigher than 10 K. Furthermore, a search inYxNiB(C1−zNz)yandYxNiBNyphase spread alloys showed no superconductivity. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.364281

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Extended electric field-current density characteristics taken on the bare cores of monofilament (Bi,Pb)2Sr2Ca2Cu3Ox(2223) tapes at 77 K have been used to measure the irreversibility field,H*, and the critical current density,Jc, at different stages of tape processing. The number of heat treatments and the uniaxial pressing pressure were the experimental variables. BothH*andJcincreased substantially with heat treatment and with deformation pressure. The data are consistent with an improvement inJcfrom two factors, one being an increase in the 2223 phase fraction with increasing heat treatment, the second, independent cause being an increase in the flux pinning properties of the composite. The experiments show that improvingJcinvolves control of at least three factors: enhancing the volume fraction of 2223 phase; increasing flux pinning; and enhancement of the connectivity of the grain boundaries that lie within the current path. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.364233

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The electric field effect on the transport properties of ultrathinY0.9Pr0.1Ba2Cu3Oychannels was examined as a function of channel thickness and channel length. Samples having a planarYBa2Cu3OxultrathinY0.9Pr0.1Ba2Cu3Oy-YBa2Cu3Oxstructure with a gate electrode on the backside of theirSrTiO3substrate were used. The channel layer exhibited superconducting properties when its thickness was more than 9 nm, whereas channels less than 7.5 nm thick were in the insulating phase of the superconductor-insulator transition. The modulation ratio of the conductance of the insulating (I)-phase channels was a few orders of magnitude higher than the modulation ratio of the carrier density. The field-effect mobility increased with increasing channel thickness when the film was in the insulating phase. The sheet conductance of channels shorter than 10 &mgr;m was higher than that of a 100-&mgr;m-long channel of the same thickness due to a size effect on the transport of the I-phaseY0.9Pr0.1Ba2Cu3Oychannel. The field-effect mobility was also enhanced by the size effect. These results imply that the performance of possible field-effect transistors with high-temperature superconductors may be much improved by utilizing an I-phase channel whose length is short enough for the size effect to be evident. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.364234

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Scaling approaches to magnetization measurements are explored on a set of melt-textured(Y1−xPrx)Ba2Cu3O7−&dgr;samples with different Pr concentrations. When normalized with corresponding scaling parametersHm,Mm,andJm,respectively, magnetic hysteresis loops and related critical current densities for different temperatures from 4.5 to 75 K are all found to exhibit scaling behavior. It is shown that for low scaled field(h)region, this behavior can be described qualitatively well based on an extended critical-state model. The effective activation energy extracted from magnetic relaxation measurements can also be qualitatively described by a scaling relation within the framework of collective-pinning theory. In addition, Pr doping is found not to influence the scaling approaches themselves up to the highest level investigated in the present work. However, the scaled magnetic hysteresis loop width, critical current density, and effective activation energy are all increased by Pr doping, further suggesting the enhancement of flux pinning for our samples. Furthermore, experimental results and fitting parameters are discussed as well with respect to relevant scaling background models. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.364291

出版商:AIP    

年代:1997

数据来源: AIP