摘要:

Spatially resolved cathodoluminescence (CL) spectrum mapping revealed a strong exciton localization in InGaN single-quantum-wells (SQWs). Transmission electron micrographs exhibited a well-organized SQW structure having abrupt InGaN/GaN heterointerfaces. However, comparison between atomic force microscopy images for GaN-capped and uncapped SQWs indicated areas of InN-rich material, which are about 20 nm in lateral size. The CL images taken at the higher and lower energy side of the spatially integrated CL peak consisted of emissions from complementary real spaces, and the area was smaller than 60 nm in lateral size. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120025

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

n-type silicon samples were measured by deep level transient spectroscopy (DLTS) immediately (within one hour of storage at room temperature, required for the preparation of Schottky-diodes) after copper diffusion and quench. A donor level atEc-(0.15±0.01) eVwith a concentration of up to1013 cm−3was detected. The amplitude of the DLTS peak decreased with the time of storage at room temperature, and stabilized at a concentration(4 to 7)×1011 cm−3after 15–20 h. The activation energies and prefactors of the decay of the DLTS peak inn-type Si and the reactivation of copper-compensated boron inp-type Si concur. This correlation suggests that the deep level is interstitial copper itself or a complex of interstitial copper. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120026

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We report on the electric-field dependent band-gap energy and near-gap absorption coefficient of a specially designed strained-layer superlattice (SLS) employing tensile strained quantum wells and having a band-gap wavelength near 1.3 &mgr;m. The SLS was grown by molecular-beam epitaxy on an InP substrate and consists ofIn0.43Ga0.57Aswells (4.5-nm-thick) andIn0.6Al0.4Asbarriers (6.75-nm-thick). For applied fields from zero up to at least2.5×105 V/cm, the band-edge absorption exhibits a single peak, which we attribute to a field-independent superpositioning of the heavy- and light-hole ground states. This result agrees with tunneling resonance calculations, which predict these hole states to have the same zero-field energy and to undergo nearly identical Stark shifts. Absorption–coefficient changes of up to104 cm−1were readily achieved with applied biases under 15 V, suggesting potential applications to optical modulator devices. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120027

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Single wavelength reflectance difference anisotropy (RDA) has been used to study the kinetics of the self-assembly of Ga atom chains on faceted Si(112) surfaces. The formation of the chains is followed from the initial deposition through changes in the surface reconstruction from(5×1)to(6×1).We present a simple Monte Carlo model to account for the time evolution of the RDA signal as a function of temperature and experimentally determined kinetic parameters. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120428

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The present investigation deals with the electrical response of palladium doped tin oxide, as a means of improving the selectivity for liquid petroleum gas (LPG) in the presence of CO,CH4. The sensor element with the composition of Pd(1.5 wt &percent;) in the base materialSnO2sintered at 800 °C, has shown a high sensitivity towards LPG with a negligible cross interference of CO andCH4at an operating temperature of 350 °C. This greatly suggests the possibility of utilizing the sensor for the detection of LPG. X-ray photoelectron spectroscopy studies have been carried out to determine the possible chemical species involved in the gas-solid interaction and the enhancing mechanism of the Pd dopedSnO2sensor element, towards LPG sensitivity. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120557

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We present the design of a novel bolometer intended for measurement of radiation within a waveguide. The thermal link in the bolometer is a low-thermal conductance micromachined beam. Power is coupled from an antenna to a resistive termination at the center of the beam. The optimization of the design for an astronomical measurement leads to an operating temperature of 0.48 K, accessible with aHe3refrigerator. Measurements on the antenna absorber in a waveguide show an average absorption of 94&percent; from 33 to 50 GHz. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120028

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

A superconducting optical flux-trap memory with a femtosecond pulsed laser is proposed and then demonstrated. The magnetic flux is trapped in a simpleYBa2Cu3O7−&dgr;thin film loop with a polarity controlled by means of optical supercurrent modulation. After removing the external bias current, the trapped fluxes are detected by observing electromagnetic pulse radiation 60 cm away from the sample, which is excited by modulating a persistent current that circulates in the loop. The mechanism for the readin of the magnetic fluxes is discussed in relation to the current distribution in the memory. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120029

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The current–voltage(I–V)characteristics and the resistive transition under magnetic field were extensively investigated onc-axis oriented YBCO polycrystalline films with a different amount of an in-plane grain alignment. All the parameters deduced from the scaling analyses in the intergranular region along with the vortex-glass-to-liquid transition indicate that the intergranular current transport is not via weak links but is due to strongly coupled channels regardless of a degree of an in-plane grain alignment. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120430

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We have found that substitution of bismuth into theTlBa2Ca2Cu3O9system leads to a high temperature superconductor with significantly greater low temperature flux pinning than that of the other copper oxide superconductors. Bi substitutes at the Tl site up to 20 at. &percent;. The superconducting transition temperatureTcincreases from 110 K forx=0.0to 116 K forx=0.2.Scanning electron microscope (SEM) images reveal a platelike morphology which is highly suitable for powder-in-tube processing. The magnetization–hysteresis loop shows that the Bi-substituted phase has significantly better low temperature flux pinning properties than the pristine Tl cuprate, and exhibits only a weak dependence on temperature and field when compared to that of unsubstituted phase. However, at 77 K the compound has lowerJc,determined magnetically, compared to that of the(Tl,Pb,Bi)Sr1.6Ba0.4Ca2Cu3Oyand Y-123 systems. The enhancement of superconducting properties is attributed to an increased coupling between theCuO2planes along thecaxis. Substitution of 20&percent; of Bi inTlBa2Ca2Cu3O9makes the compound an excellent choice for magnet wire applications at relatively low temperatures. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120030

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We have developed a non-ion-etching ion-beam-assisted-deposition (IBAD) process for fabricating high critical-temperature(Tc)grain boundary Josephson junctions through a photoresist liftoff mask. TheYBa2Cu3O7(YBCO) junctions fabricated through this process exhibited the resistively-shunted-junction (RSJ)-likeI–Vcharacteristics. The well-defined Shapiro steps have been seen on theI–Vcurves under microwave radiation. The magnetic modulation of critical current of a 4 &mgr;m width YBCO junction tallied with the prior simulated Fraunhofer diffraction pattern of a Josephson junction with a spatially homogeneous critical current density. The maximum peak-to-peak modulation voltage across the dc superconducting quantum interference device (SQUID) fabricated by using these junctions reached up to 32 &mgr;V at 77 K. The magnetic modulation of the SQUID exhibited periodic behavior with the observed modulation period of5.0×10−4 G.©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120031

出版商:AIP    

年代:1997

数据来源: AIP