摘要:

Thin Si3N4films were grown on Si by direct exposure to a low‐temperature (250–650 °C) nitrogen glow discharge at 13.56 MHz. The activation energy for growth is 0.3±0.12 eV. Their chemical and electronic, bulk, and interfacial properties are studied as a function of the film thickness and growth temperature. The ultrathin films (d<100 A˚) exhibit an average breakdown field of 10–12 MV/cm, a dielectric constant equal to 5.5, and are effective barriers against oxidation at 1000 °C. Conduction in ultrathin films is via Fowler–Nordheim tunneling over the temperature range 77–420 K. Deep‐level transient spectroscopy analysis reveals the presence of two majority‐carrier (hole) traps at the interface, with activation energies 0.1 and 0.35 eV, respectively. The trap atEV+0.35 eV is attributed to the Si dangling bond defect while the trap atEV+0.1 eV could be attributed to a structural defect that isinsituannealed at growth temperatures higher than 500 °C. The interface state concentration is a sensitive function of the growth temperature and varies in the range 8×1010–6×1012cm−2.

ISSN:0021-8979    

DOI:10.1063/1.348460

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

Effects of the parameters characterizing the electron‐transport properties in an In0.52Al0.48As/In0.53Ga0.47As/In0.52Al0.48As double heterostructure are theoretically investigated using the Monte Carlo approach. The calculated results are compared with the previously measured electron velocity versus electric‐field relationship for the investigated structure. It is found that the effects of the &Ggr;‐valley nonparabolicity factor and the intervalley energy separations in In0.53Ga0.47As are the most remarkable within the investigated parameters.

ISSN:0021-8979    

DOI:10.1063/1.348461

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

The density of occupied interface states as a function of energy in nonohmic polycrystalline Bi‐doped ZnO was obtained using photocapacitance measurements. Peaks in the interface states’ densities were observed at depths of 2.46 and 2.79±0.08 eV from the bottom of the conduction band. The combination of these two states was found in photoconductance measurements on Bi‐doped samples of ZnO and not found in undoped samples; thus, these states were assumed to be related to interface states that arise from doping with Bi.

ISSN:0021-8979    

DOI:10.1063/1.348435

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

Films of Bi2Sr2CaCu2Oyhave been prepared by diffusing Bi2CaCu2O5into Sr2CaCu2O5. Examination by x‐ray diffraction and scanning electron microscopy showed a highly preferred orientation of columnar grains with the [100] axis normal to the surface. The maximum oriented texture was for a film thickness of 76 &mgr;m for thicknesses between 51 and 150 &mgr;m. The preferred orientation existed up to the surface of the sample, and there was no evidence of an unreacted region at the surface when the diffusion was done for at least 3 days. The films had the usual superconducting transition of the 2212 phase.

ISSN:0021-8979    

DOI:10.1063/1.348410

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

Thin and ultrathin Co/Pt multilayered structures have been prepared on glass substrates by electron‐beam evaporation at room temperature and by sputtering at various substrate temperatures and sputtering pressures. Perpendicular magnetic anisotropy was found in samples with Co/Pt bilayer thicknesses near 3 A˚/10 A˚ and total thicknesses of the layer stack of no greater than 300 A˚. X‐ray diffraction was performed on the samples to determine layer spacing and integrity, and possible crystallinity of films. Crystalline structures in the interface between the Co and Pt layers were found and identified. The effects of sputtering parameters, such as pressure and substrate temperature, on the magneto‐optical Kerr effect were studied. The two deposition methods, electron‐beam evaporation and sputtering, resulted in different magneto‐optical properties in samples with the same nominal layer structures. We have also investigated optical properties (reflectance, index of refraction, and extinction coefficient) of these materials using ellipsometry.

ISSN:0021-8979    

DOI:10.1063/1.348411

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

Micromagnetic structures are computed for pairs of 180° domain walls in thin films, driven together by applied magnetic fields. It is shown that the field required to annihilate the walls depends strongly on their relative symmetry. There are six possible symmetries for pairs of walls, two of which show no resistance to annihilation. For the other four symmetries, the applied field needed to annihilate the walls varies by large amounts according to the symmetry. The resistance to annihilation decreases with increasing film thickness. Experimental studies of interactions of domain‐wall pairs, in which examples of both low and fairly high resistance to annihilation have been observed, provide qualitative support for these results. It is concluded that wall interactions can contribute significantly to the coercivity of soft magnetic films.

ISSN:0021-8979    

DOI:10.1063/1.348412

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

The polarized neutron reflectivity (PNR) of cobalt/copper multilayer films has been measured close to the critical edge for total reflection. Prominent features in the scattered neutron intensity, such as the superlattice diffraction peaks and the positions of the critical edge for total reflection, are sensitive to both the magnetic and structural properties of films, making PNR a useful tool for the characterization of magnetic metallic superlattices. The films were prepared by sputter deposition and the sample composition was measured by Rutherford backscattering spectroscopy. It has been found that while the density of the sputtered copper/cobalt multilayers is approximately 5% less than the bulk metals, the cobalt magnetic dipole moment per atom is little changed compared to the bulk. Evidence is also found for oxidation of the top cobalt layers.

ISSN:0021-8979    

DOI:10.1063/1.348413

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

This paper reports on an original work on the study of the behavior of ZnO‐based varistor by ac impedance measurements. The measurements of complex impedance response to small ac signals applied to samples have been achieved in the frequency range 10−3–7×106Hz and a temperature range −196–145 °C. In the temperature range below −120±10 °C, a complete semicircular relaxation phenomenon has been observed, which is in good agreement with the Debye model. In the temperature range above −120±10 °C, the appearance of the depression angle &thgr; may arise from the heterogeneity of the barriers of the ceramic varistor. A Cole–Cole distribution function of the relaxation time constants was used to characterize the response of the ceramic device as a function of temperature. No observable influence in the response was introduced by either the space charge or the electrode. Using the leakage resistance measurements from the complex plane, two values of the activation energies were observed; 0.36±0.02 eV and 0.01±0.001 eV. Similarly, the boundary layer equivalent capacitance measurements detect two other energy levels: 0.06±0.005 eV and about 0 eV.

ISSN:0021-8979    

DOI:10.1063/1.348414

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

Microwave dielectric parameters are measured for lithium‐zinc ferrites with chemical formula Li0.5−x/2Fe2.5−x/2ZnxO4(x=0.0, 0.1, 0.3, 0.5, 0.6). All the samples exceptx=0.5, show an increase in the dielectric loss with temperature. A relaxation‐type mechanism is observed forx=0.5. The results are compared with the low‐frequency dielectric constant and loss.

ISSN:0021-8979    

DOI:10.1063/1.348415

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

We present a theory correlating the excitonic photoluminescence linewidth in quantum wells with the microscopic structure of the interface in the presence of a magnetic field. The interface is described in terms of microscopic fluctuations &dgr;1and &dgr;2where &dgr;1is the local fluctuation in the well width and &dgr;2is the lateral correlated extent of the fluctuation. We use Lifshitz’s theory of disordered alloys to determine the probability distribution of fluctuations of the well size over the effective extent of the optical probe, namely, the exciton. The line shape is then calculated from this distribution. We have evaluated the fullwidth at half maximum (&sgr;) for both the heavy‐hole exciton and the light‐hole exciton as a function of the well size and interface parameters &dgr;1and &dgr;2in the presence of a magnetic field in GaAs‐Al0.3Ga0.7As and In0.53Ga0.47As‐InP quantum well structures. We find that for a given set of values of well width and interface parameters, the application of the magnetic field reduces the effective size of the exciton and thus increases the linewidth.

ISSN:0021-8979    

DOI:10.1063/1.348416

出版商:AIP    

年代:1991

数据来源: AIP