摘要:

We report on the mechanisms of optical gain in cubic GaN. Intensity-dependent gain spectra allow a distinction of the processes involved in providing optical amplification. For moderate excitation levels, the biexciton decay is responsible for a gain structure at 3.265 eV. With increasing excitation densities, gain is observed on the high energy side of the cubic band gap due to band filling processes. For the highest pump intensities, the electron-hole plasma is the dominant gain process. Gain values up to210 cm−1were obtained, indicating the high potential of cubic GaN for device applications. The observed gain mechanisms are similar to those of hexagonal GaN. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120588

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Self-focusing of ps laser pulses (&lgr;=790 nm) due to the nonlinear Kerr effect is shown to provide an easy and flexible method for producing bulk structures with dimensions on the order of 10 &mgr;m without damaging the entrance or exit surfaces of the material. The depth at which damage occurs can be controlled by adjusting either the pulse energy or pulse length. A study of the dependence of structure depth on the square root of the laser power for a given pulse length provides a straightforward method for determining the nonlinear index of refraction (Kerr coefficient),n2. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120606

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

The comprehensive parameter space of self-oscillation and its period-doubling route to chaos are shown for bounded beam-plasma systems. In this parametrization, it is helpful to use a potentially universal parameter in close analogy with free-electron-laser chaos. A common parameter, which is related to the velocity slippage and the ratio of bounce to oscillation frequencies, is shown to have similar significance for different physical systems. This single parameter replaces the dependences on many input parameters, thus suitable for a simplifying and diagnostic measure of nonlinear dynamical and chaotic phenomena for various systems of particle-wave interactions. The results of independent kinetic simulations verify those of nonlinear fluid simulations. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120589

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Single and double Langmuir probe analyses have been realized in the wafer region of an electron cyclotron resonance reactor in its distributed configuration. Results in nitrogen gas have shown unambiguously that two electron populations exist in this region: one with low temperature (about 1–2eV) and high density and the second with higher temperature (about 8 eV) and lower density. Measurements in silicon nitride deposition plasma (nitrogen and silane gases) have been successfully realized and have shown that these two populations are also present. Finally, we try to correlate the plasma parameters (electron temperatures and densities and ions’ energy) to the deposited film parameters (deposition rate and refractive index). ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120608

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

The surfaces of insulating alumina particles have been coated with high-temperature superconductingYBa2Cu3O7−xand colossal magnetoresistivePr0.65Ba0.05Ca0.3MnO3−xfilms. These coatings on particulate surfaces have been realized using a technique which is based on laser-assisted generation of a homogeneous flux of ablated materials in front of a fluidized bed of host particles. The coated particulates have been characterized using scanning electron microscopy, energy dispersive x-ray analysis, Auger electron spectroscopy, and superconducting quantum interference device magnetometer. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120590

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

We have investigated the possibility afforded by epitaxial ferroelectric oxide thin films to control and image locally the polarization field of ferroelectrics over large areas with submicron resolution, using the metallic tip of an atomic force microscope as a mobile top electrode and local probe of the ferroelectric properties. Atomically smooth films ofPb(Zr0.2Ti0.8)O3,showing a root-mean-square roughness of typically a few angstroms, could be uniformly polarized and imaged over areas as large as2500 &mgr;m2without introducing any topographic disorder. Regular arrays of 100 nm wide lines and circular domains with a diameter less than 100 nm were written in arbitrary areas of the uniformly polarized regions. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120591

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

A two-dimensional thermodynamic model was developed to account for the observed difficulty in the fabrication of epitaxialPb(Zr,Ti)O3(PZT) thin films in which tetragonal and rhombohedral phases coexist. The thermodynamic formalism based on the Landau–Devonshire’s phenomenological theory predicts the enhanced thermodynamic stability of the tetragonal-phase field under a two-dimensional compressive stress. We have experimentally proved this prediction by fabricating an epitaxially oriented tetragonal PZT thin film on MgO substrate with the target composition corresponding to the bulk morphotropic phase boundary (MPB). ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120609

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

In order to better understand and model internal gettering of iron in silicon, a quantitative investigation of iron precipitation in silicon containing different oxygen precipitate densities was performed. The number of iron precipitation sites was obtained from the iron precipitation kinetics using Ham’s Law. At low temperatures, the iron precipitate density corresponded to the oxygen precipitate density. A strong temperature dependence of the iron precipitate density was observed for the samples with larger oxygen precipitate densities. These data were used to simulate iron precipitation during a slow cool. From those simulations, optimal cooling rates were obtained for different silicon materials assuming various iron precipitation site densities in the epitaxial layer. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120592

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

The low-temperature grown AlGaAs/GaAs multiple quantum well structures were characterized by photoluminescence (PL) spectroscopy. The samples were grown at 270–400 °C and annealed at 500–900 °C. After anneal, photoluminescence quenching was observed for the samples grown at temperatures below 350 °C, and found to show a strong dependence on the growth and anneal temperatures. The luminescence intensity for the PL-quenched sample exhibits a power law dependence on the excitation level with an exponent close to 2, indicating a bimolecular recombination process in parallel with strong nonradiative recombination. The photoluminescence quenching upon anneal is attributed to the formation of arsenic clusters that serve as new nonradiative recombination channels. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120593

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

The effects of AlAs wet oxidation on overlayers were investigated using InGaAs/GaAs strained-layer superlattice structures grown on an AlAs layer. The superlattice partially relaxes towards its equilibrium spacing as the result of the oxidation of the underlying AlAs layer. Double-crystal x-ray diffraction measurements were used to determine the degree of strain relaxation. Larger relaxation is observed for the sample with a higher indium composition and a thicker AlAs layer. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120594

出版商:AIP    

年代:1998

数据来源: AIP