摘要:

We have designed and demonstrated a narrow bandpass filter, which is composed of a double‐barrier structure, for an infrared hot‐electron transistor with a cutoff wavelength at 14 &mgr;m. The filter is capable of suppressing the low energy thermally assisted tunneling current as well as the high energy thermionic emission current that are not degenerate with the photoelectrons. As a result, the detector can be operated at 77 K with a 45% BLIP level and an estimatedNE&Dgr;Tof 38 mK. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.114156

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The fundamental properties of In0.2Ga0.8As/GaAs strained‐layer quantum‐wells (QWs) grown on (311)A GaAs substrates were studied. The radiative and nonradiative recombination rates as a function of temperature were obtained from the photoluminescence (PL) spectra and the time‐resolved PL measurements. The radiative recombination rate is enhanced in (311)‐oriented QW structures as compared to (100)‐oriented ones. We fabricated graded‐index separate‐confinement heterostructure double quantum‐well lasers on (311)A GaAs substrates. We demonstrate the low threshold current density of 360 A/cm2for a 1.17 mm long laser at room temperature. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.114157

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

We discuss measurements of buried interfaces utilizing x‐ray specular reflectivity profiles, and high‐resolution x‐ray reflectivity measurement of diffuse scattering. Interface structure is compared to atomic force microscopy characterization of the morphology of the Si cap layer overlying the buried structures. The results show that the morphology of roughness on the growth surface is greatly influenced by substrate miscut, and tends to form one‐dimensional undulations. Roughness along the miscut direction is highly replicated from interface to interface, but roughness perpendicular to the miscut evolves more rapidly during the growth process. This effect is characterized by a reduced vertical correlation length in x‐ray diffuse scattering in one azimuthal orientation. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.114158

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

We present results on a near‐field scanning probe microwave microscope which is based on the nonlinear behavior of a YBa2Cu3O7direct‐current superconducting quantum interference device (SQUID). Our system has a spatial resolution of about 30 &mgr;m and derives its probing field from circulating currents in the SQUID loop. The frequency is set by the Josephson relation and is continuously tunable up to about 200 GHz. By imaging small patterned normal metal thin‐film samples of Cu and Nb at 77 K, we have confirmed the operating bandwidth of the system and investigated the nature of the imaging process. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.114159

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

We demonstrate that recent data on the length and temperature dependence of the critical current in Josephson junctions with YBa2Cu3O7−xelectrodes coupled by Ca‐ and Co‐substituted YBa2Cu3O7−xinterlayers are consistent with the conventional theory of the proximity effect. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.114174

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

All thin‐film YBCO/Pb Josephson tunnel junctions have been fabricated. The junctions showed a well‐defined Pb gap, Pb phonon structures, and very low leakage current. In addition, a higher bias spectroscopy revealed identical structures as have been seen in junctions made with single‐crystal YBCO. A thin uniform Ag diffusion barrier at the junction interface lowers the junction resistance enough to study the Josephson effct in YBCO/Pb tunnel junctions. Both the temperature and the magnetic field dependencies of the magnitude of the Josephson current displayed conventional behavior. The junctions were very reproducible and uniform as indicated by theIc(B) pattern. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.114160

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The flux change &dgr; &Fgr; through a bistable superconducting quantum interference device has been measured in the presence of thermally induced switching (with rate &Ggr;) versus &dgr; &Fgr;x, the change in the applied flux. For small &dgr; &Fgr;x, &dgr; &Fgr; is proportional to &dgr; &Fgr;xwith a measured flux gaing, depending on the temperature, barrier height, and frequency &OHgr;, with a maximum of about 16. In agreement with theories of periodically driven stochastic bistable systems,g(&OHgr;) is nearly frequency independent up to &Ggr; and is proportional to &OHgr;−1for &OHgr;≫&Ggr;. For larger amplitude signals, harmonic generation has been measured in the adiabatic limit (&OHgr;≪&Ggr;) and found to be in good agreement with theory. Possible applications of this system for flux measurement are discussed. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.114161

出版商:AIP    

年代:1995

数据来源: AIP

ISSN:0003-6951    

DOI:10.1063/1.114163

出版商:AIP    

年代:1995

数据来源: AIP

ISSN:0003-6951    

DOI:10.1063/1.114164

出版商:AIP    

年代:1995

数据来源: AIP