摘要:

Thin oxide on strained Si1−xGexsurface has been grown using a nonelectron cyclotron resonance mode microwave plasma at low temperatures (150–200 °C). An optimized post‐oxidation and post‐metal annealing cycle has resulted in very low fixed oxide charge density (1.78×1010/cm2) and moderately low interface trap density (2.9×1011/cm2 eV). A controlledinsituhydrogen‐plasma treatment to Si1−xGexhas been found to be useful in improving the electrical properties of the oxide. The high electron injection phenomena of metal oxide semiconductor capacitors has been used for charge trapping studies of sites normally present in the SiGe oxides. From the position and the extent of current ledge observed as a function of ramped gate voltage, the capture cross section and the total number of traps have been determined. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.360556

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The transport properties of InP and GaAs epitaxial layers grown on exactly (001)‐oriented Si substrates were investigated by temperature‐dependent van der Pauw measurements combined with anodic stripping. Electron concentrationsnatT=300 K decreasing from around 1018cm−3at the heterointerface to a constant level of 1016cm−3toward the surface agree well with the concentration profile of Si donors. Their activation energy is 2.9 and 1.3 meV in InP/Si and GaAs/Si, respectively. At low temperatures a marked decrease of the electron mobility &mgr; at the heterointerface occurred. A quantitative analysis of &mgr; (T) led to the model of charged dislocations as scattering centers. By comparison with the dislocation densities of 2×108and 1×108cm−2in the vicinity of the surface of 2‐ and 3‐&mgr;m‐thick layers found by wet chemical etching we derived the occupation probability of the charged centers along the dislocation lines as 0.2 and 1.0 for InP and GaAs, respectively. At 300 K &mgr; was almost unaffected by dislocation scattering and values of 3600 cm2/(V s) (InP) and 3800 cm2/(V s) (GaAs) fornof 2×1016and 8×1016cm−3were obtained which are close to the values found with homoepitaxial layers. ©1995 American Institute of Physics. 

ISSN:0021-8979    

DOI:10.1063/1.360557

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

In this work, we have numerically integrated in space and time the effective mass Schro¨dinger equation for an electron in a GaAs/AlAs quantum well. Considering the electron–phonon interaction and an external electric field, we have studied the electronic tunneling escape process from semiconductor quantum wells. In this way, electronic lifetimes have been obtained at different well widths and applied electric fields. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.360558

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Perovskite La1−xCaxMnO3−&dgr;thin films were deposited on MgO(001) substrates using pulsed laser deposition. Effects of deposition conditions, such as laser fluence, substrate temperature, and oxygen pressure, on growth behaviors of the films were investigated over a wide range. Epitaxial La0.7Ca0.3MnO3−&dgr; /MgO thin films were able to be growninsituunder conditions such as 1.5–2.1 J/cm2laser fluence, 650–750 °C substrate temperature, and 100–300 mTorr oxygen pressure. The oxygen pressure during the deposition is found to be closely related to crystalline orientations of the films. Rutherford backscattering spectroscopy measurements show that the epitaxial La1−xCaxMnO3−&dgr;thin films have compositions similar to those of targets, demonstrating that pulsed laser deposition is a useful technique to get thin films with complicated chemical compositions. The magnetoresistance, −&Dgr;R(6T)/R(0), of the La0.7Ca0.3MnO3−&dgr; /MgO thin film was about −80%, which is smaller than the reported values (i.e., ∼−99.92%) of the La–Ca–Mn–O thin films on LaAlO3substrates [S. Jin, T. H. Tiefel, M. McCormack, R. A. Fastnacht, R. Ramesh, and L. H. Chen, Science264, 413 (1994)]. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.360687

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

An amorphous bimetal ribbon consisting of magnetostrictive (Fe40Ni40B20) and nonmagnetostrictive (Co67Fe4Cr7Si8B12) layers was prepared by planar flow casting from a double‐chamber crucible. The effect of applied tensile stress on hysteresis loops and the surface domain structures of the stress‐relieved bimetal was investigated at room temperature. The hysteresis loops can be well explained by superpositions of hysteresis loops of the individual layers. Only the magnetostrictive layer is responsible for the influence of applied stress on magnetic behavior. At a certain stress, the magnetic anisotropy of the magnetostrictive layer abruptly changes from a hard‐ribbon‐axis to an easy‐ribbon‐axis type. This transition is accompanied by a change of domain structure and a sharp maximum of the coercive field. A simple model taking into account an interplay of the applied tensile stress with the compressive stress produced by thermal contraction after stress relief and/or by bending of the ribbon has been developed. The observed behavior can be well explained by the model. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.360559

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

An effective cluster model has been developed [Phys. Rev. B42, 9319 (1990)] that treats a disordered suspension of monodisperse metal spheres as a mixture of isolated spheres and close‐packed spherical clusters of spheres using the Clausius–Mossotti or Maxwell equations. The effective cluster model is adapted to such suspensions with a random intermingled cluster topology using Bruggemann’s symmetrical equation. Model susceptibilities for the two cluster topologies are contrasted with one another and compared with experiments. Guillien’s permittivity measurements [Ann. Phys. (Paris) Ser. 1116, 205 (1941)] and Turner’s conductivity measurements [Chem. Eng. Sci.31, 487 (1976)] exemplify nonpercolating island topology suspensions. The permittivity measurements of Grannan, Garland, and Tanner [Phys. Rev. Lett.46, 375 (1981)] exemplify percolating random topology clusters. The models for both cluster topologies are in excellent agreement with experiment over the entire accessible range of volume loading. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.360560

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Statics of 90° domain structures formed in a thin tetragonal film epitaxially grown on a cubic substrate is studied theoretically on the basis of a rigorous solution of the associated elasticity problem. Inhomogeneous internal stresses existing in the strained polydomain epitaxy are calculated by the method of fictitious dislocations distributed along domain boundaries and the film/substrate interface. The calculation properly takes into account the influence of the film free surface on the field of internal stresses. For both possible periodic laminar structures, the energies of elastic strain fields existing in the film and the substrate are evaluated. These results are used to compute the equilibrium geometric parameters of periodic domain structures that minimize the total internal energy of a polydomain epitaxy. The dependencies of the equilibrium parameters on the film thickness and the relative misfit strain between the substrate and film are described. By comparing the minimum internal energies associated with various domain configurations, a diagram of equilibrium domain patterns is developed. In the range of relative misfit strains lower than some critical value, two threshold film thicknesses exist, separating three stability regions of domain patterns which correspond to a monovariant film and two periodic domain structures. In the rest of the diagram, a pattern consisting of equivalent domains with the tetragonal axes parallel to the interface is stable, irrespective of the film thickness. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.360561

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Characteristics of the photoluminescence (PL) from disordered and ordered GaAs/Al0.3Ga0.7As superlattices are compared. The disordered superlattices (DSL) are nonperiodic and the ordered superlattices are periodic. The PL emission is much stronger in the DSLs by a factor that depends on the PL excitation wavelength and excitation power. These observations are interpreted in terms of an enhanced radiative decay rate in the DSLs brought about by the breakdown of translational symmetry in these systems. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.360562

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Silicon wafers implanted with 30 keV He ions at room temperature in a low pressure hydrocarbon atmosphere exhibited visible photoluminescence. The samples were characterized by Raman, infrared, transmission electron microscopy, and heavy ion elastic recoil detection analysis. Two different layers were distinguishable on top of the silicon, with the upper layer comprising mostly amorphous carbon, as confirmed on a similarly implanted Be sample. Green photoluminescence was found to arise from the thinnera‐Si1−xCx:H interface layer. Such a buried intermixed layer could be incorporated into a stable visible light emitting device based on crystalline silicon. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.360563

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

An easy and very reproducible method to produce porous silicon by light‐stimulated etching of crystalline silicon in HF is described, and the formation mechanism is discussed in terms of carrier diffusion and band bending near the surface. The method avoids the use of electrodes and electrochemical etching. The photosynthesized porous silicon shows bright photoluminescence. Spectra recorded at room temperature forn‐type as well asp‐type silicon are presented. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.360564

出版商:AIP    

年代:1995

数据来源: AIP