摘要:

We have investigated the structural and optical properties of rare earth-doped zinc tellurite glasses modified by the substitution ofZnF2.Raman and phonon sideband spectroscopies were employed to characterize changes in the glass structure as well as to probe vibrational behavior in the immediate vicinity of the rare earth ion. These measurements are combined with photoluminescence and optical absorption to monitor the effect of halide substitution upon the optical behavior of the rare earth dopant. A substantial increase in the intrinsic radiative lifetime ofNd3+is observed with increasing halide concentration. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.119756

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

TiN(001)[100]‖Si(001)[100] parallel epitaxy of thin films grown by pulsed reactive crossed-beam laser ablation (KrF, 248 nm) is investigatedin situby reflection high-energy electron diffraction andex situby x-ray diffraction, full-hemispherical X-ray photoelectron diffraction and low-energy electron diffraction. TiN films are grown on atomically flat, initially two domain 2×1 reconstructed Si(001) surfaces at100⩽T⩽800° C.Parallel epitaxy is found to prevail atT⩾400 °Cwith growth rates in the10−2monolayer/pulse−1range and a repetition rate of 2 Hz. The substrate and film morphologies are investigated using atomic force microscopy. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.119757

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We report results on an improved growth process for cubic boron nitride (c-BN) films. The films are deposited on a dc-biased silicon substrate using ion-assisted sputtering. First, we grow a BN template layer at a bias voltage which maximizes thesp3content. After this template layer attains a thickness of ∼500 Å, corresponding to the coalescence of the mosaiclike grain structure, we find that we can reduce the substrate bias to about 50&percent; of its initial value while sustaining pure phase c-BN growth. The reduction in nitrogen ion energy results in a dramatic increase in the growth rate as well as significantly improved film quality. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.119429

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The capability of misfit dislocations to generate nanostructures in the bulk ofSi1−xGex/Siheteroepitaxial systems is demonstrated. It is shown that dislocation slip originating from compositionally gradedSi1−xGexlayers can produce a range of low-dimensional structures including nanowires, nanodots, and mosaic superlattices. Formation of the nanostructures is achieved in parallel processing, through a simple two-step cycle which includes growth of layered planar structures and postgrowth annealing. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.119758

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We describe a technique for direct measurement of the passive optical mode loss of a semiconductor laser or similar semiconductor waveguide structure, based upon measurement of the attenuation of optically excited luminescence in the guided mode as a function of distance traveled along the passive guide. A spectrometer is used to select luminescence in the low energy tail of the spectrum which is subject to very little reabsorption. We have applied the method to a series of highly strained GaInP quantum well laser structures and observe an increase in the mode loss from9.9 cm−1for 1&percent; strain to46 cm−1for 1.7&percent; strain. This correlates with the appearance of clustered regions in the highly strained wells observed by transmission electron microscopy (TEM). ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.119759

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Low temperature nitridation of silicon oxide layers by nitrogen plasma generated by electron impact is investigated using x-ray photoelectron spectroscopy (XPS) and synchrotron radiation ultraviolet photoelectron spectroscopy and it is found that a large amount of nitrogen can be incorporated in the layers. The valence band structure of the oxide surface nitrided at 25 °C is similar to that ofSi3N4,while that nitrided at 700 °C resembles the mixture of silicon oxide and silicon oxynitride. Measurements of XPS depth profiles show that the nitrogen concentration is high near the surface and the oxide/Si interface. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.119760

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Optical absorption measurements were performed on a series of thin GaN epilayers. Sharp spectral features were observed due to the1sAandBexciton transitions. Using polarization dependent absorption, theCexciton transition was identified. A broad absorption feature was observed at ∼3.6 eV, which is attributed to indirect exciton-phonon absorption. The excitonic structure was found to persist well above room temperature. A fit to the Varshni formula yielded a temperature dependence ofE(T)=E(T=0)−11.8×10−4T2(1414+T)eV for theAandBexcitons. The exciton absorption linewidth was studied as a function of temperature, indicating that GaN exhibits very large exciton-phonon coupling. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.119761

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Metal impurity release from structural defects in polycrystalline silicon was studied following thermal treatments, and, in addition, a correlation between impurity distributions and structural defects was established. Impurities were mapped with synchrotron-based x-ray fluorescence in the as-grown state, after rapid thermal annealing and following aluminum gettering treatments. The goal of this work was to determine if impurity release from structural defects limits gettering of metal impurities. The results reveal that nickel and copper metal impurities are primarily found at dislocations in as-grown crystals, and the release of these impurities from defects occurs rapidly with no apparent barrier to dissolution. Gettering treatments dissolved metal impurity precipitates to <2–5 nm in radii; however, the material performance was not greatly enhanced. ©1997 American Institute of Physics. 

ISSN:0003-6951    

DOI:10.1063/1.119762

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Blueshifts in the photoluminescence emission energies from an ensemble of self-assembled InAs quantum dots are observed as a result of postgrowth thermal annealing. Enhancement of the integrated photoluminescence emission and narrowing of the full width half-maxima (from 55 to 12 meV) occur together with blueshifts up to 300 meV at annealing temperatures up to 950 °C. Evidence that the structures remain as dots comes form the observation of level filling and photoluminescence excitation studies which reveal LO phonon peaks occurring at multiples of∼30 meVfrom the detection energies. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.119763

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The growth mechanisms of GaN grown on a GaN buffer deposited onto sapphire substrates are studied here. The growth rate was measured at different temperatures versus ammonia flow and was found to decrease with increasingNH3flow. This surprising behavior is modeled in terms of competitive adsorption of species on the growing surface. Very good agreement is obtained between the model and the experimental data. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.119764

出版商:AIP    

年代:1997

数据来源: AIP