摘要:

Quantum wells of GaAs lattice matched to GaP have been studied by photoluminescence and electroreflectance. The quantum well thickness was varied between 1 and 6 monolayers in steps of 1 monolayer. Electron-hole transitions have been observed involving states both in theXband and in the&Ggr;band, which have been modeled using a k.p. model in conjunction with the envelope function approximation. Overall agreement between theory and experiment is found using an unstrained valence band offset of 0.6 eV. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.119198

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We create a reservoir of hole traps in a resonant tunneling light emitting diode by etching thep-type contact into an array of nanometer scale pillars. In the off state, the charge reservoir keeps the light output extremely low, even at relatively high currents. The device can be switched on to produce light by raising the electron emitter past a confined electron state allowing holes to escape from the nonradiative region. The resulting electro-optic switch has an on/off ratio of at least 1000:1, a large improvement over conventional resonant tunneling light emitting diodes. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.118215

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We report the observation of tunneling induced transparency in asymmetric double quantum well structures. Resonant tunneling through a thin barrier is used to coherently couple the two upper states in a three level system of electronic subbands in a GaAs/AlGaAs structure. This creates Fano-type interferences for the collective intersubband excitations in the absorption from the ground state, analogous to electromagnetically induced transparency (EIT) in atomic systems. We observe a 50&percent; reduction in absorption between the subband resonances which can be explained by taking into account the coherent coupling of the upper states. We analyze the bias dependent absorption spectra and determine the relevant lifetime broadening and dephasing rates for the transitions. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.119199

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The selective deposition of compound semiconductors on single crystal silicon tip arrays produces optical quality, direct band gap materials on the silicon nanostructures. We demonstrate using the organometallic vapor phase epitaxy of GaInP that the direct band gap semiconductor nucleates selectively on the silicon tips. The structural properties of the tips (whose radius of curvature is approximately 10–20 nm) are unaltered by this chemical vapor deposition process. Furthermore, intense band edge emission from the GaInP is observed with an external electron beam or laser stimulation indicating a good crystal quality for the three dimensional epitaxial structures. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.119200

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The deposition of particulate species, typically seen in pulsed laser deposition can be eliminated by the deployment of a line-of-sight shadow technique. Since the technique uses the discrimination between ballistic and diffusive species, it is important to understand the lateral stoichiometry and thickness dependence under various deposition conditions. We present in this study the dependence of the lateral thickness and stoichiometry ofYBa2Cu3O7−xdeposited by a shadow mask pulsed laser technique on the background oxygen pressure and the shadow mask position from the target. We determined Y atoms to be limiting the lateral stoichiometric uniformity. Due to its diffusive nature, shadowed pulsed laser deposition also allowed us to improve the thickness uniformity across the wafer. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.119201

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Narrow and low-lossYBa2Cu3O7−&dgr;(YBCO) transmission lines for use in multichip modules have been attempted to be developed. 18-cm-long YBCO coplanar transmission lines with widths down to 5 &mgr;m were prepared by a composite patterning process combining Ar-ion milling and wet-etching. The transmission losses of the packaged 5-, 10-, and 25-&mgr;m-wide lines, respectively, were −1.57, −0.85, and −0.55 dB at 20 GHz and 55 K. These values provide similar surface resistances of 0.59–0.80 m&OHgr; at 20 GHz and 55 K. This indicates successful fabrication of a 5-&mgr;m-wide YBCO coplanar line without notable extrinsic loss increase resulting from process damage. The attenuation constants of these lines are approximately two orders of magnitude lower than for 10-&mgr;m-wide Cu microstrip lines. These results show that the YBCO coplanar lines with widths down to 5 &mgr;m have great potential for use in multi-chip modules. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.119202

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The structure and magnetic properties ofGd2Co17−xAlxcompounds were investigated. All samples have a rhombohedralTh2Zn17-type structure and the replacement of Co by Al results in an approximately linear increase in the unit cell volumes at a rate of 8.2Å3/Al. The Curie temperature decreases monotically with the increase of Al concentration. On the basis of magnetization curves at the compensation temperature, the intersublattice-molecular-field coefficient,nRT,and the RT exchange-coupling constantJRThave been determined. It is noteworthy that the substitution of Al has a significant effect on the magnetocrystalline anisotropy of the Co sublattice, and changes the easy magnetization direction ofGd2Co17−xAlxcompounds from the basal plane to thecaxis. ©1997 American Institute of Physics. 

ISSN:0003-6951    

DOI:10.1063/1.119258

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Degradation progress in polymeric electroluminescent devices during device operation was clarified byin situmeasurement of photoluminescence image change using time resolved confocal laser scanning microscope. It is found that the degradation stems from two kinds of dark spots, which have the dented circle shape and the dome shape. Dented circle shapes grow during the operation. Dome shapes, where the polymer layers are detached from the indium-tin-oxide electrode, appear suddenly and do not change in size. Comparison of the Auger analysis depth profiles of the dented and the normal sites indicates that the polymer layer at the dented sites disappears. Time-resolved confocal laser scanning microscopy is found to be a powerful technique to analyze the degradation process. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.118516

出版商:AIP    

年代:1997

数据来源: AIP