摘要:

NanocrystallineBaTiO3has been prepared by a gas-condensation process.BaTiO3and Ti sources are vaporized simultaneously in either a helium or an oxygen environment using an electron beam evaporation system. The stoichiometry of nanocrystallineBaTiO3powders can be controlled precisely and reproducibly. NanocrystallineBaTiO3powders, with an average particle size of less than 20 nm, can be obtained by postannealing the as-evaporated powders at a temperature of 700 °C. These powders show good sintering behavior with a high density at a sintering temperature as low as 1250 °C. Differential thermal analysis indicated that nanocrystallineBaTiO3was formed through the reaction of Ba/Ti oxidized clusters. Dielectric properties of ceramics from nanocrystallineBaTiO3are also reported. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.118828

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Mechanisms of strain relaxation and defect formation during surface roughening inSi1−xGexfilms grown epitaxially on (100)Si substrates have been investigated by controlled annealing experiments. Epitaxial films 10 nm in thickness and containing 18&percent; Ge, which are subcritical with respect to the formation of misfit dislocations, show strain relaxation through surface roughening on annealing at 850 °C, where surface grooves are aligned along ⟨100⟩ directions. Other films with 22&percent; Ge and supercritical thicknesses have also been studied, where surface grooves are aligned along ⟨110⟩ directions. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.118819

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The behavior of the oxidation-induced stacking-fault ring (OSF ring) in Czochralski (CZ)-grown silicon crystals is predicted based on the dynamics of point defects during growth. Preexponential constants for the equilibrium point defect concentrations and diffusivities are determined by fitting the predictions of the model to a single set of experimental data for OSF-ring dynamics. Other experimental data is well fit by this model. Moreover, point defect properties used are consistent with other estimates. Asymptotic analysis of the point defect model leads to a closed-form expression for the dependence of the OSF-ring location on processing conditions and thermophysical properties of point defects at the melting temperature. These results indicate that differentiation between defect types in CZ-grown material can be done entirely on the basis of point defect dynamics. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.118829

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We have investigated a novel way to dope porous Si layers with (B) and/or (P) using the spin-on doping technique. Under certain conditions, pore filling by the dopant solution was measured to be near 90&percent;–95&percent; leading to a homogeneous coverage of the porous skeleton. Near two orders of magnitude decrease in diode resistance was achievable following rapid thermal activation in aN2atmosphere of B only or B+P double doped porous Si. Photoluminescence (PL) intensities observed in B+P double doped porous layers were significant. Relative to as-prepared samples, the PL intensities of double doped samples were weaker for porous Si onn-type and stronger for porous Si formed onp-type Si. In both cases, the PL magnitudes after double doping were comparable. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.118830

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The possibility of fabricating quantum dots under Volmer–Weber growth mode is investigated. Layers of ZnSe/ZnS were grown by metalorganic chemical vapor deposition on both Si and GaAs substrates. The images of surface morphology, taken by atomic force microscopy, showed that the layers were grown in three-dimensional islands. Blueshift was observed in the photoluminescence spectra up to room temperature for these samples. This blueshift was shown to originate from the ZnSe islands. The effect of ZnSe growth duration was investigated. It was found that the blueshift increased with shorter ZnSe growth durations, but this near band gap emission disappeared when the ZnSe growth duration was longer than 5 s. Effects of quantum confinement and strain were considered to resolve the origin of the blueshift. Our result suggests that carrier confinement plays a dominant role. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.118831

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Zn1−xCdxSe (x≈0.5), a II–VI wide band gap semiconductor, is grown lattice matched by molecular beam epitaxy on (001) InP substrates. The effect of incorporating an InP buffer layer on structural and optical properties of the ZnCdSe films is studied. Transmission electron microscopy shows that a reduction in the density of stacking faults by two orders of magnitude (from5×109down to5×107/cm2) is realized by use of the buffer layer. Grown-in Shockley-type stacking faults are the only defects observed in the ZnCdSe. The (004) x-ray diffraction rocking curve becomes as narrow as 73 arcsec, and the photoluminescence emission peak becomes narrower and more intense. The lower defect density is attributed to the overall improved InP surface allowing for better two-dimensional nucleation of II–VI growth.©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.118832

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

In this letter, it is shown that micro-Raman spectroscopy allows easy, nondestructive determination of the C49 and C54 phase of titanium silicide with &mgr;m resolution within single structures with area dimensions down to 1×1&mgr;m2and along isolated line structures with widths down to 0.25 &mgr;m. The micro-Raman spectroscopy technique is used to study isolated 0.25–5-&mgr;m-wideTiSi2lines with thicknesses as small as 16 nm that are formed in both crystalline Si and polycrystalline Si. The phase mapping ability of the technique is demonstrated on several 80-&mgr;m-long, 0.35-&mgr;m-wideTiSi2lines that are part of four-terminal line resistance devices created using complementary metal–oxide–semiconductor processing. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.118833

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The structures of light emitting porous and nanocrystalline silicon films have been investigated using high resolution electron microscopy. A pseudo-ordered structure has been found from the Fourier transformation of the high resolution images after digital processing of the images. The structure description was distinguished from common amorphous and nanocrystalline silicon films. The formation mechanism of the pseudo-ordered structure is described in the letter. ©1997 American Institute of Physics. 

ISSN:0003-6951    

DOI:10.1063/1.118834

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We have synthesized GaN nanocrystals by sequential implantation of Ga and N ions into a sapphire substrate followed by a postimplantation anneal. The nanocrystals have been identified as the wurtzite phase &agr;-GaN structure by transmission electron microscopy. We also found that the nanocrystals are aligned with the sapphire following the relationship:(0001)sapphire∥(0001)GaNand(112¯0)sapphire∥(112¯0)GaN.The use of a sapphire substrate allows for the measurements of optical properties, and near band-edge luminescence and the yellow band are observed in photoluminescence spectroscopy.

ISSN:0003-6951    

DOI:10.1063/1.118850

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Using vibrating optical beam, differential reflectance (DR) spectra have been obtained on GaAlAs thin films and GaAs bulk subjected to an externally applied temperature gradient. The DR spectra reveal all the critical points, namely,E0andE0+&Dgr;0in GaAlAs andE0,E0+&Dgr;0andE1in GaAs in the given energy range under study whereas, without the temperature gradient, DR spectra measured on homogeneous materials are structureless. The DR technique shows better sensitivity than photoreflectance on thin epilayers. Our investigation suggests that, combined with the application of a field gradient, DR can be made extremely useful for the characterization of semiconductors. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.118835

出版商:AIP    

年代:1997

数据来源: AIP