摘要:

We have studied the gain characteristics of gain‐guided quantum well II–VI laser diodes by measuring the amplified spontaneous emission spectra under several pulsed conditions. The temperature rise during one current pulse affects the gain characteristics and theL‐Icharacteristics. The net modal gain at constant peak current increases with the pulse width. The peak gain for long pulses shows a superlinear dependence on injection current. In this case, theL‐Icurve is very steep above threshold and sometimes shows an internal quantum efficiency of more than unity. This leads to an underestimation of the internal cavity loss giving a value inconsistent with the one obtained from the gain spectra. With short pulse currents (<200 ns), the peak gain shows a weak sublinear dependence on injection current. The cavity losses obtained from the gain spectra and theL‐Icharacteristics at short pulses are consistent. As a result, we obtain the intrinsic gain characteristics of gain‐guided quantum well II–VI laser diodes. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.117561

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

We present a useful and simple technique to prepare controllable Er‐doped Si thin films using KrF excimer laser ablation. The sharp intense photoluminescence (PL) at 1.54 &mgr;m originating from the intra‐4fshell transition in Er3+ions was observed from 18 K up to room temperature. Characteristics of PL thermal quenching and time decay of prepared Er‐doped Si thin films are very similar to those of Er‐doped porous Si and/or Er‐doped amorphous Si. Furthermore, observation of Er3+emission from as‐prepared thin films without thermal annealing suggests that the Er doping in the form of Er atomic radical species produced by laser ablation is essential in activation of Er3+ions. Moreover, incorporating a prescribed amount of Er in the bulk target enables us to control the Er doping level in thin films prepared by laser ablation. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.117562

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

The interaction of intrinsic oxygen in Czhochralski silicon with implantation damage induced by 2.0 MeV Si+ions has been investigated as a function of annealing temperature and time. Four distinct regions of oxygen localization are revealed by secondary ion mass spectrometry following sample annealing. The different regions are correlated with either a near surface vacancy‐rich region or the buried layer of extended defects near the projected range. The relative concentration of oxygen in each region depends on the competition between oxygen gettering in each region and out‐diffusion to the surface. It has been established, using quasikinematical and dynamical contrast transmission electron microscopy imaging techniques, that the oxygen in regions containing extended dislocations is in the form of fine precipitates. The precipitates decorate both the dislocations and, for faulted loops, the stacking fault planes. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.117563

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

The coalescence of diamond grains grown by microwave plasma chemical vapor deposition was observed at an atomic level using high resolution electron microscopy in combination with scanning electron microscopy. It was shown that large diamond crystals can be grown either by a coalescence of two [001]‐oriented grains which have a slight misorientation or by a switch of the grain boundary, which is usually perpendicular to the surface plane, to a parallel direction. A single crystalline film might be deposited when the growing surface is fully covered by the (001) plane, i.e., no {111} top facet appears to separate the growing (001) surface. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.117564

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Low temperature two‐photon fluorescence excitation microscopy was used to obtain fluorescence spectra of single CdSe colloidal nanocrystals or quantum dots. The fluorescence spectra reveal large, 0.02 eV shifts of the peak emission wavelength on times of the order of 100 s were also observed in some instances. We attribute this behavior to excited state coupling to photoinduced changes at the nanocrystal surface. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.117565

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Highly split, visible light emissions at room temperature were observed in the range from 335 to 650 nm in silicon‐rich oxide films deposited in the plasma phase of a mixture of silane and oxygen. The mechanism of the light emissions is classified into two categories. The photoluminescence bands at both 365 and 469 nm are related to the intrinsic defects of theE′ center and the neutral oxygen vacancy, respectively. However, the relatively sharp peaks at 403 and 535 nm are correlated with the development of polycrystalline core of Si‐enriched parts. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.117566

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

The uniform deposition of YBa2Cu3O7(YBCO) thin films over an 8‐in.‐diam. area, using a 3‐in.‐diam. sputtering target and optimized substrate rotation in a single target 90° off‐axis sputtering technique, is reported. Two dimensional maps of the thickness profile of YBCO films deposited on a stationary substrate have been obtained using surface profilometry. These thicknesses were used in a computer simulation to predict which distance of the target from the center of the substrate rotation will produce the maximum area with uniform thickness. The films deposited on substrates mounted on a rotating arm displayed uniform thickness (<±5% variation) and composition (<2.3% deviation from the target stoichiometry) and a consistently high transition temperature (Tc>87.5° K) and critical current density (Jc 4.2 K>2×107A/cm2) over an 8‐in.‐diam area. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.117567

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

The temperature dependence of the critical current in planar high‐TcJosephson junctions fabricated in YBa2Cu3O7thin films by focused electron irradiation has been studied. It is shown that in the range of critical current densities spanning more than five orders of magnitude and temperature range 0.1≤T/Tc≤1, the critical current densityjcvaries as (1−T/Tc)2. TheTdependence of the critical current, however, is affected by the transition from the narrow junction to the wide junction limit asjcincreases. An expression for the Josephson penetration depth in thin‐film coplanar structures is derived, and magnetic field penetration depth in junction banks is extracted from theIc(T) dependences. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.117568

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Alloys of Fe49Co49V2(Hiperco Alloy 50) (Hiperco is a registered trademark of CRS Holdings, Inc.), both annealed and thermally aged, were studied using anomalous synchrotron x‐ray and neutron powder diffraction. Rietveld and diffraction profile analysis indicated both anincreasein the structural order parameter and a small latticeexpansion(∼0.0004 A˚) after aging at 450 °C for 200 h. In addition, a cubic minority phase (<0.3%) was identified in the ‘‘annealed’’ sample, which increased noticeably (0.3%→0.8%) as a result of aging. The presence of antiphase domain boundaries in the alloys was also revealed. These results directly correlate with the observed changes in the magnetization behavior and challenge the notion that a ‘‘fully’’ ordered Fe–Co alloy demonstrates optimum soft magnetic properties. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.117569

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Observations of electron paramagnetic resonance by means of the angular momentum absorbed by a small sample are reported. The method is based on the detection of the torque induced in a microcantilever, like the ones employed in atomic force microscopy, integral with the sample. The results obtained with this experimental scheme are compared with the ones of the Sidles–Rugar method exploiting a force detection of the magnetic resonance in presence of strong magnetic field gradients. In particular, the signal drawn by angular momentum absorption shows opposite trends when the static magnetic field is swept in opposite directions, contrary to the case of experiments performed with force detection. The shape of the signal is characterized at different values of the static field and of radiation intensity. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.117570

出版商:AIP    

年代:1996

数据来源: AIP