摘要:

Phonon-limited inversion layer electron mobility in extremely thin (100) Si layers of silicon-on-insulator field-effect transistors has been studied at 300 K using a relaxation time approximation and a one-dimensional self-consistent calculation. For the Si layer thicknesstSiof more than approximately 5 nm, the mobility behavior as a function of an effective vertical electric field is found to be almost identical with that of bulk Si inversion layers. For a thickness of less than that, however, the mobility behavior is considerably affected by the change in the electronic structures due to a confinement effect. As the Si layer thickness decreases, the phonon-limited electron mobility&mgr;phincreases to a maximum attSiof∼3 nmand decreases monotonically. The increase in mobility results from the increase of the fraction of electrons in the lowest energy subband that has a higher mobility than other subbands. The mobility decrease in the extremely thintSiregion is attributed to the enhancement of phonon scattering rates caused by a reduction of the spatial widths of the subbands. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366480

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

A new algorithm of the analysis of the electrical conduction in the layers forming a semiconductor structure has been described. In the algorithm, in contrast to earlier approaches, the mobility spectrum technique has been applied to the sheet conductivity tensor. The standard carriers parameters have been estimated from the tensor components in the high and low magnetic field limits. The proposed method has been illustrated by the analysis of results of the electrical conduction measurements versus magnetic field performed up to 1.6 T at 77 K in a molecular beam epitaxial (MBE) grown GaAs:Si structure. The sample was an MBE GaAs:Si layer grown on a buffer epilayer. As a result of the analysis, the mobility spectra and the standard parameters describing carriers in different layers have been found. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366481

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We have observed the population of the third(n=3)two-dimensional electron subband of InGaAs/InAlAs modulation-doped structures with very dense sheet carrier density by means of Fourier transform photoluminescence (PL). Three well-resolved PL peaks centered at 0.737, 0.908, and 0.980 eV are observed, which are attributed to the recombination transitions from the lowest three electron subbands to then=1heavy-hole subband. The subband separations clearly exhibit the features of the stepped quantum well with triangle and square potential, consistent with numerical calculation. Thanks to the presence of the Fermi cutoff, the population ratio of these three subbands can be estimated. Temperature and excitation intensity dependence of the quantum well luminescence intensity is also analyzed. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366482

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

It is shown that the annealing under Ar of sputteredWSxamorphous films deposited on Ni coated substrates gives bidimensional polycrystalline2H–WS2films. Ni enhances the formation of large crystallites. The temperature dependence of the mobility and its dependence versus the Ni content clearly show that transport properties are governed by grain boundaries. A basic grain boundary model like the model of Seto is well suited to explain the electrical properties. The photoconductivity enhancement resulting from nickel is assigned to a decrease of the number of the electrical barriers. However, noise measurements are not consistent with Hall measurements; a model is thus proposed to explain the1/fnoise excess in relation to the traces of Ni–W revealed by x-ray diffraction. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366483

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We have measured the magnetic hysteresis loops of an epitaxialYBa2Cu3O7−&dgr;thin film using our recently developed device which can provide the field magnitude in the range of 0–1000 Oe and the field sweep rate up to107 Oe/s.The shape of the hysteresis loop measured changes with the field-sweep rate up to the critical sweep rate; and over the critical sweep rate the ac magnetization reaches its real critical state where magnetization does not change even with a further increase in the field-sweep rate. The critical sweep rate is about106 Oe/sat 77 K. With the hysteresis loops and Bean model, we have calculated the magnetization critical current density(Jcac)which is consistent with that obtained byI–Vmeasurements. We have also studied flux motion and activation energy under the high sweep rate magnetic field. At temperature 77 K, the velocity of the flux motion is of the order 10 m/s and the pinning energyU0/kis about 339 K which is much smaller than the magnetization decay measurement. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366484

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The possibility of predictably enhancing the critical current density of a bulk material with a strong uncorrelated disorder by introducing linearly correlated defects into just the top and bottom surface layers has been investigated. The task was fully demonstrated for melt-texturedYBa2Cu3O7−&dgr;having irradiation modified percent thickness ranging from 13&percent; to 5&percent;. The characteristic signatures of vortex localization were observed in the higher range of temperature and magnetic field. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366485

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Standard treatments of the magnetization reversal of fine particles yield a reversal mechanism that begins with nucleation of a nonuniform or uniform energy barrier state that involves virtually the entire sample volume. Accordingly, the barrier height is essentially proportional to the sample volume. Such strong volume dependence is not observed, especially in measurements of thermally activated reversal. Numerical micromagnetic analysis also shows a variety of surface reversal modes depending on the ratio of the particle size to the exchange length. An analytic model for surface nucleation is presented here for an idealized system to illustrate this phenomenon. The corresponding barrier height does not depend on sample volume, though it may depend on surface area. Any additional size dependence will arise from the finite front velocity with which the reversal propagates. An example of thermally activated reversal is given that shows “effective” reversal volumes that correspond to these surface reversal modes, and thus, can be much smaller than the sample volume. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366486

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The universally used approximation for the magnetostriction constant of a polycrystalline material is based on the assumption of uniform stress through the aggregate. In this article we calculate the alternative approximation of uniform strain. The calculation is performed in terms of the grains orientation distribution (texture) function, and single crystal constants describing the elastic and magnetostrictive anisotropy. These bounds represent the optimum solution of the incompletely specified problem of crystallites shape distribution in a polycrystalline aggregate. The available experimental data are compared with the two approximations. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366487

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We have found a novel method for increasing the giant magnetoresistance (GMR) of Co/Cu spin valves with the use of oxygen. Surprisingly, spin valves with the largest GMR are not produced in the best vacuum. Introducing5×10−9Torr(7×10−7Pa) into our ultrahigh vacuum deposition chamber during spin-valve growth increases the GMR, decreases the ferromagnetic coupling between magnetic layers, and decreases the sheet resistance of the spin valves. It appears that the oxygen may act as a surfactant during film growth to suppress defects and to create a surface which scatters electrons more specularly. Using this technique, bottom spin valves and symmetric spin valves with GMR values of 19.0&percent; and 24.8&percent;, respectively, have been produced. These are the largest values ever reported for such structures. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365620

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Microfabricated magnetoresistive elements based on either the anisotropic or the giant magnetoresistance effect were tested for their frequency dependent resistance noise behavior at room temperature in a dc magnetic field, using a dc sense current. Thermal resistance noise was the dominant noise source above about 10 kHz. At low frequencies the resistance noise was found to be dominated by a1/fcontribution that depends on the applied magnetic field. The1/fnoise is relatively low and field independent when the element is in a saturated state and contains a relatively large and field dependent excess contribution when the magnetic field is in the sensitive field range of the element. The1/fnoise level observed in saturation is comparable to the1/fnoise level found in nonmagnetic metals; the excess noise has a magnetic origin. The variation of the excess noise level with the applied dc magnetic field can be explained qualitatively using a simple model based on thermal excitations of the magnetization direction. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366533

出版商:AIP    

年代:1997

数据来源: AIP