摘要:

Nitrogen doping in ZnSe using a new type of electron-cyclotron-resonance (ECR) source has been investigated. Selective nitrogen radical doping is performed using the ECR source with an external electrode, which can remove charged particles in the nitrogen plasma by the electrode applied electric field. Nitrogen ions are trapped by the electrode and the ion current is measured as a function of the electric field. The activation ratio of nitrogen atoms is investigated for various doping conditions by comparing the carrier profile and the atomic nitrogen profile, which are measured by capacitance–voltage techniques and secondary ion mass spectrometry. It was confirmed that nitrogen ions are removed and do not play a role asp-type dopants in ZnSe growth by molecular beam epitaxy. The activation ratio of nitrogen atoms is increased by removing the nitrogen ions. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.118644

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

InAs/(GaIn)Sb superlattices (SL) grown by solid-source molecular-beam epitaxy were studied by spectroscopic ellipsometry. The pseudodielectric function of InAs/GaSb SLs could be fitted using modified bulk dielectric functions of InAs and GaSb with pronounced energy shifts and broadening of critical-point resonances. These changes in the dielectric functions of the constituent layers can be explained only in part by pseudomorphic strains, therefore providing evidence for thin-layer critical-point broadening and quantum confinement effects. For InAs/(GaIn)Sb SLs, the extremum in the pseudodielectric function derived from theE1critical point of (GaIn)Sb was found to shift to lower energies with increasing In content, and thus can be used as a probe for the composition of the (GaIn)Sb SL layers. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.118560

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The polarization dependence of the Franz–Keldysh effect (FKE) in metalorganic vapor phase epitaxially grown AlGaInP/GaInP/AlGaInPp-i-ndouble heterostructures was investigated for samples with different ordering parameters. We determine an ordering induced shift of the FK spectra of up to 13 meV between light polarized along the [011] and [01-1] crystal directions. Due to the FKE the transmitted light intensity ratio between the respective polarizations was changed from 0.2 to 2.8 dB by applying an electric field of 335 kV/cm. ©1997 American Institute of Physics. 

ISSN:0003-6951    

DOI:10.1063/1.118561

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We use a plan-view transmission electron microscope technique to unambiguously image the “physical” interface position between Si and furnace grownSiO2layers. As-grown ∼6-nm-thick (100) oxides have a very high roughness (&sgr;∼10–15 Å), which can be removed by short annealing in an inert gas at a growth temperature of 900 °C. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.118562

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The thermoluminescence (TL) of ZnS nanoparticles is reported. The TL intensity increases as the particle size is decreased. The consistency of the size dependence of the TL with that of the surface fluorescence indicates that the TL may be related to the surface states. TL may be caused by the recombination of carriers released from the surface states or defect sites by heating. Smaller particles have higher surface/volume ratio and more surface states, therefore contain more accessible carriers for TL. Besides, the carrier recombination rate increases upon decreasing size due to the increase of the overlap between the electron and hole wave functions. These two effects may make the TL increase upon decreasing size of the particles. The appearance of TL prior to any radiation reveals that trapped carriers have pre-existed. The investigation of TL may provide some useful information about the surface states that may explain the size dependence of the surface fluorescence. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.118563

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Surface acoustic wave (SAW) velocity and attenuation measurements have been performed on high-temperature superconductingYBa2Cu3O7−&dgr;(YBCO) thin films (deposited on nonpiezoelectric substrates), and YBCO single crystals. A “bridge” technique is employed in which piezoelectric substrates, patterned with interdigital transducers, are bonded to the sample under investigation. The temperature dependence of 168 MHz SAW attenuation in a single crystal near its superconducting transition has been measured in applied magnetic fields up to 1.6 T. Features are seen above the superconducting transition temperature which may be indicative of a transition in the electric polarization of the material. A field-dependent attenuation peak, seen in the superconducting state, is discussed in terms of the theory of thermally activated vortex motion. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.118564

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Phase intergrowth among some kinds of the Bi2Sr2Can−1CunOyphases is observed in the thin film fabrication at ultralow co-deposition with multitargets by means of ion beam sputtering. The molar fraction of the Bi2212 phase in the mixed crystal of the grown films is investigated as a function of the applied ozone pressure and the substrate temperature. The activation energy for the phase transformation from the Bi2201 to the Bi2212 is estimated in terms of the Avrami equation. This study reveals that the formation of a liquid phase contributes significantly to the construction of the Bi2212 phase in the thin films, differing from the bulk synthesis. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.118565

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Thick superconducting films ofYBa2Cu3O7−&dgr;grown by photoassisted metalorganic chemical vapor deposition that have shown a decrease ofJcwith increasing thickness (>1 &mgr;m) have been exposed to ion irradiation in an attempt to enhanceJc.A 4.5 &mgr;m thick film irradiated with 1 MeV protons at a dose of3×1014/cm2has shown an increase ofJcby a factor of nearly20–1.7×106 A/cm2corroborating the proposal that a lack of pinning centers in the grown thick films, due to their high crystalline quality, contributed to the observed decrease ofJcwith increasing film thickness. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.118566

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Large positive magnetoresistance (LPMR) effects have been measured at temperaturesT<100K in epitaxial Cr/Ag/Cr trilayers grown by molecular beam epitaxy. Compared to single Ag films, the magnetoresistance at 4.2 K is enhanced by nearly two orders of magnitude reaching values up to 120&percent; in a field of 8 Tesla. This behavior is related to a drastic modification of the electron scattering at the Ag interfaces due to the presence of the buffer and cap Cr layers. The LPMR curves measured at different temperatures demonstrate a scaling behavior typical for electron transport in two-dimensional systems. The magnitude of the LPMR is a function of temperature and residual resistance ratio and is influenced by the direction of the applied magnetic field. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.118567

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Carbon nanotube sheet electrodes have been prepared from catalytically grown carbon nanotubes of high purity and narrow diameter distribution, centered around 80 Å. Our study shows that the electrodes are free-standing mats of entangled nanotubes with an open porous structure almost impossible to obtain with activated carbon or carbon fiber. These properties are highly desirable for high power and long cycle life electrochemical capacitors. Specific capacitances of 102 and 49 F/g were measured at 1 and 100 Hz, respectively, on a single cell device with 38 wt &percent;H2SO4as the electrolyte. The same cell had a power density of>8000W/kg. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.118568

出版商:AIP    

年代:1997

数据来源: AIP