摘要:

The majority‐carrier trapping cross section for a majority‐carrier trap can be obtained using capacitance spectroscopy by monitoring the kinetics of trap filling. This method cannot be applied for the determination of the trapping cross section of minority carrier by this majority‐carrier trap because the capture or emission kinetics cannot be observed. Here we propose a method to measure the minority‐carrier trapping cross section for majority‐carrier trap. It is not a general method but limited to defects which have the property to anneal under minority‐carrier injection, a rather common feature in III‐V and II‐VI semiconductor compounds. For such defects, the annealing rate induced by injection is proportional to the rate of minority carrier trapping. As a result, the study of the annealing rate versus the density of injection and versus the temperature allows us to obtain the minority‐carrier trapping cross section and its variation with temperature. The method is illustrated by a study of the so‐calledE3 defects, created by electron irradiation at room temperature inn‐type GaAs. For this defect, we find a minority‐carrier cross section which is thermally activated with an activation energy of ∼0.35 eV, implying that the capture of minority carriers, like the capture of majority carriers, occurs through multiphonon emission. A discussion of this result in terms of configuration coordinate diagram shows the limitation of this model.

ISSN:0021-8979    

DOI:10.1063/1.336602

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

A method to represent the effect of ionized impurity scattering in Monte Carlo calculations is presented. It is based on a model of B. K. Ridley [J. Phys. C10, 1589 (1977)] and does not have the computational disadvantages of the Brooks–Herring and Conwell–Weisskopf models.

ISSN:0021-8979    

DOI:10.1063/1.336603

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

Metal‐oxide‐semiconductor field‐effect transistors with very thin (100–400 A˚) gate oxides are fabricated. With improved procedures for extracting the various physical parameters from the capacitance‐voltage curves and carefully controlled experiments, it is confirmed that the fixed oxide charge density increases inversely with the oxide thickness. The surface mobilities at both room temperature and 77 K are also characterized. It is found that the mobility in general decreases as the oxide thickness is reduced. The mobility results are interpreted in terms of the coulomb and surface roughness scattering. A plausible model explaining the correlation of oxide thickness, growth condition, and the above physical parameters is also proposed.

ISSN:0021-8979    

DOI:10.1063/1.336604

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

Experimental data are presented for the substrate current (holes), which accompanies electron injection into the oxide ofn‐channel field‐effect transistor structures, in the tunneling regime. Dependencies of the effect on oxide thickness and on the metal gate material were investigated. An inverse relation was found between the initial rise time of oxide current transients and both the electron and hole currents. It is shown that these initial current increases are related to positive charge, therefore a correlation exists between the positive charge and electron or hole currents. The strength of impact ionization in SiO2is discussed on the basis of band‐structure arguments and it is concluded that there are difficulties in explaining the substrate current by impact ionization. A technique for fast measurements of capacitance‐voltage shifts at the end of an applied high field pulse is described.

ISSN:0021-8979    

DOI:10.1063/1.336605

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

In single‐flux quantum (SFQ) memory cell operation, a stochastic phenomenon occurs in certain ranges of bias current. These regions, in which the memory cell stochastically switches to the voltage state or to the other vortex mode, are called the gray zone. The gray zone reduces the operating margin of the cell, because the bias current region in the gray zone must be avoided for memory operation. It is very important to investigate the origin of the gray zone for the design of the cell. But the gray zone has not ever been discussed in detail. We have studied memory operation from the viewpoint of the thermal fluctuation of the potential energy of the cell. Our conclusions are as follows. (1) The gray zone originates in bias current fluctuations, caused by the thermal fluctuation of the potential energy of the cell. (2) In the gray zone the probability of transition to the voltage state does not necessarily increase monotonically with the bias current. This is because the transition to the voltage state occurs in several bias current regions, even if there is no thermal fluctuation, for a memory cell with the large McCumber factor.

ISSN:0021-8979    

DOI:10.1063/1.336606

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

Superconducting critical temperaturesTcand magnetic fieldsHc2, lattice parametersa0, and chemical compositions were measured for ‘‘bulk’’ layers (∼6 &mgr;m or greater) of ‘‘pure’’ and alloyed Nb3Sn which were made by the bronze process. The values ofTc,a0, and the composition of pure Nb3Sn layers were ∼18 K, 0.52900±0.00005 nm, and 25±0.5 at. % Sn, respectively, independent of heat‐treatment temperature (between 650–780 °C) and of the bronze composition, as long as the thickness of the layers was greater than ∼6 &mgr;m. Small additions of Ti (∼1 at. %) or Ta (∼3 at. %) slightly increased the value ofTc(by ∼0.2–0.4 K) above that for pure Nb3Sn. However, additions of larger amounts of these elements or addition of other transition elements (V, Zr, and Mo) significantly decreasedTc. Also, small additions of these elements significantly increasedHc2. Specifically, the largest values ofHc2(∼27 T at 4.2 K) were obtained for Nb3Sn layers containing ∼1.5 and ∼4 at. % of Ti and Ta, respectively, compared with a value for the pure Nb3Sn of 23.5 T at 4.2 K. The value ofa0decreased with all of the alloying additions; these variations can be explained qualitatively by several models for the lattice parameter of A15 compounds, but none of them can quantitatively predict the variations. In one system, (Nb,Ti)3Sn, values of the normal‐state resistivity just above the transition temperature were measured: adding 3 at. % Ti raises the value to ∼55 &mgr;&OHgr; cm from the value of 10–15 &mgr;&OHgr; cm for pure Nb3Sn. This increase in the resistivity is thought to be a primary reason for the increasedHc2for this system as well as the other types of alloyed Nb3Sn which were studied here.

ISSN:0021-8979    

DOI:10.1063/1.336607

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

A cavity consisting of a superconducting lead film on a sapphire substrate has been fabricated to obtain the enhanced frequency stability possible with this configuration. The cavity exhibits a quality valueQexceeding 2×109in its TE011mode with a resonant frequency of 2.689 GHz. Methods of fabrication and testing of the cavity are presented in this article. Since the interface between the film and substrate is exposed to the full value of the resonant magnetic field, our experiment is the most sensitive test to date for enhanced losses at the interface itself. We find no evidence of such losses. In fact, the measured values of the surface resistance match very well predictions for rf losses based on the BCS theory.

ISSN:0021-8979    

DOI:10.1063/1.336608

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

Amorphous rare‐earth transition metal alloys of composition (Gd1−xFex)1−yAuywithx=0.74, 0.77, and 0≤y≤0.40 were prepared by evaporation onto rotating glass substrates. The magnetic and magneto‐optic properties have been investigated in the temperature range 4.2≤T≤TCrevealing a decrease of the compensation and Curie temperature, the uniaxial anisotropy, and the Faraday and Kerr rotation with increasing gold content. The temperature behavior can be interpreted in terms of a mean‐field analysis indicating a pronounced influence of the gold on the iron moment and the exchange constants. The temperature dependence of the Faraday rotation can be described in terms of the sublattice magnetizations inferred from the fit of the mean‐field theory to the measured saturation magnetization.

ISSN:0021-8979    

DOI:10.1063/1.336609

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

The theoretical basis of the transmission line model (TLM), a model widely used to describe the propagation of flux in thin‐film magnetic structures, is examined. The primary prediction of the model is that magnetic flux propagates along the structure exponentially with a characteristic length, simply related to the permeabilities and thicknesses of the films constituting the structure. To examine the validity of the model we analyze the solution of Maxwell’s equations for two canonical thin‐film geometries and establish the following results. For the first geometry, infinite in extent, we show how the exponential flux propagation of the TLM emerges directly from the exact solution for the flux, and we derive the range in parameters over which this occurs. For the second geometry, which is of finite extent and thus includes end effects, we show that the TLM is exact in a certain limit. Practical device geometries, for which the TLM was developed (magnetic recording heads), typically approach this limit. Therefore, the solution for the magnetization in these structures will approach the limit solution, i.e., the TLM solution, and may thus, validly, be approximated by it. The physical content of this limit is discussed relative to the range of validity of the TLM. These two results confirm the general soundness of the TLM and provide a theoretical basis for it.

ISSN:0021-8979    

DOI:10.1063/1.336610

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

The temperature dependence of the saturation magnetization and the magnetocrystalline anisotropy field have been measured on single‐crystal samples of the R2Fe14B compounds for R=Y, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, and Tm from 4.2 K to the magnetic ordering temperatures. A spin reorientation transition of the Nd2Fe14B type has been found in Ho2Fe14B at 57.6 K in zero field. Another type of spin reorientation caused by anisotropy compensation between the Fe and the R sublattices exists in Er2Fe14B and Tm2Fe14B. The temperature dependence of the angle of the easy direction of magnetization from thecaxis has been measured for R=Nd, Ho, Er, and Tm. The relation between the magnetocrystalline anisotropy and the sublattice magnetization is investigated by employing a simplified two‐sublattice molecular field model.

ISSN:0021-8979    

DOI:10.1063/1.336611

出版商:AIP    

年代:1986

数据来源: AIP