摘要:

Low‐frequency noise in a hysteric rf superconducting quantum interference device (SQUID) originating from fluctuations of critical current of a weak link is considered. Such noise can be due to trapping‐detrapping processes within the tunnel barrier or to the presence of structural defects with internal degrees of freedom in the surrounding of the weak link. The defects can switch between two (or more) metastable states due to interaction with the thermal bath. On the other hand, elastic (and electric) fields created by defects act upon the critical current of the weak link inducing its fluctuations in time. Such noise is most important for high‐TcSQUIDs at high enough temperatures when defects are effectively interacting with the thermal bath. The dependencies of the intensity and statistics of flicker noise on the SQUID’s parameters and operating regime are analyzed. It is shown that higher correlation functions of output voltage at a given driving current can provide some information on the mechanism of 1/fnoise in rf SQUIDs.

ISSN:0021-8979    

DOI:10.1063/1.352874

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Highly conductingp‐type CdTe films were grown by photoassisted hot‐wall‐beam epitaxy using Li3N as a dopant source. Doping levels can be controlled fromp=4×1016to 2×1018cm−3, as determined by Van der Pauw measurements. The hall mobility ranges from 30 to 100 cm2/V s, depending on the hole concentration. Photoassisted growth enhances the incorporation of dopants by one order of magnitude and decreases the growth rate.

ISSN:0021-8979    

DOI:10.1063/1.352854

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

‘‘Coreless defects’’ are one of the long‐standing surprises of silicide epitaxy on Si. For symmetry reasons a NiSi2or CoSi2film cannot grow over a step on Si(100), but must incorporate a dislocation; apparently, however, very thin films avoided this dislocation by introducing a trench through the silicide, the coreless defect. Here we use high‐resolution microscopy, electron diffraction and dark‐field imaging to show that these defects are in fact microtwins ≊4 atomic planes thick. The twins are highly unusual in that they follow curved lines, apparently dictated by steps at the interface. A mechanism for the formation of these curved twin defects by repeated formation of a 1/12⟨111⟩ interfacial partial at steps is postulated.

ISSN:0021-8979    

DOI:10.1063/1.352829

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Continuous wave and pulsed optical beam induced current measurements were carried out onn‐InP/n‐InGaAs/n‐InP double heterostructures which contain large areas of diffused InGaAsp‐njunctions. The flat cw photocurrent and illumination‐position independence of the transient photocurrent response, observed when the optical source spot illuminates a floating diode, demonstrates the effect of photocarrier spreading in ap‐njunction. The very long photocarrier spreading length observed at low optical power may be an important parasitic coupling mechanism which should be considered in the isolation‐design of integrated optoelectronic devices.

ISSN:0021-8979    

DOI:10.1063/1.352830

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

We have numerically investigated the surface states for the case of lower‐surface potential barrier and found several low‐energy Tamm states [Physik Zeits Sowjetunion1, 733 (1932)]. Localized above‐barrier states are also found in our calculations.

ISSN:0021-8979    

DOI:10.1063/1.352831

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

The effective response of a random nonlinear composite consisting of a nonlinear material with a displacement‐electric field relation of the formD=&egr;B0E+&khgr;B‖E‖&bgr;Erandomly embedded in a host with a linearD‐Erelation is studied. Using the Maxwell–Garnett approximation and taking into account the correction to the local field in the presence of nonlinear inclusions, expressions are derived for the effective response to the order of &khgr;Band &khgr;B2, which are valid in the dilute limit of the nonlinear component in the composite.

ISSN:0021-8979    

DOI:10.1063/1.354071

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Photoluminescence measurements were carried out to investigate the dependence of the optical properties ofp‐CdTe andp‐Cd0.96Zn0.04Te on various relative concentrations of bromine in a mixture of methanol and bromine. As the bromine concentration increased, the intensity of the luminescence increased; additionally, an exciton bound to a neutral acceptor (A°X) peak at 1.588 eV inp‐CdTe was resolved into an exciton bound to neutral donor (D°X) peak at 1.592 eV and anA°Xpeak. The mixed bands of the 1.574 and 1.546 eV peaks were well resolved by using an etching bromine concentration of 2%; in particular, the intensities of theD°Xand 1.574 eV peaks increased as much as five and seven times, respectively. The intensity of the peak at 1.48 eV related to defects also increased. The intensity ofA°Xat 1.609 eV inp‐Cd0.96Zn0.04Te changed slightly with the bromine concentration. The intensities of the luminescence peaks due to the recombination of the electrons in conduction band with acceptors and to the defect relation did not vary. These results indicated that the number of Cd vacancies could be reduced due to the addition of Zn.

ISSN:0021-8979    

DOI:10.1063/1.352832

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Photoluminescence measurements were carried out in order to investigate the dependence of the optical properties ofp‐Cd0.96Zn0.04Te single crystals on hydrogen passivation conditions. After thep‐Cd0.96Zn0.04Te was annealed at 500 °C in a Cd atmosphere for 5 h, the luminescence due to the recombination of the electrons in the conduction band with acceptors (eA°) and to the donor–acceptor pair (DAP) transitions disappeared. After thep‐Cd0.96Zn0.04Te was hydrogenated, the intensity of the exciton luminescence increased so that the (eA°) and DAP peaks related to the Cd vacancies disappeared, and the defect band in the low energy range between 1.4 and 1.5 eV also vanished. These results indicate that hydrogen atoms passivated not only shallow donors but also deep acceptor impurities and that the hydrogen atoms were separated from the hydrogenated samples at 400 °C due to their thermal energy.

ISSN:0021-8979    

DOI:10.1063/1.352833

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Epitaxial superconducting Bi2Sr2CaCu2Ox(BSCCO) thin films have been formed by solid phase epitaxy from amorphous films deposited by metallorganic chemical vapor deposition. (100) MgO and LaAlO3single crystals were used as the substrates. After high‐temperature annealing in flowing oxygen, the films consist predominantly of the BSCCO (2212) phase and are epitaxial to the LaAlO3with thecaxis perpendicular to the substrate surface. The epitaxial structure of the films is confirmed by x‐ray diffraction measurements including &thgr;/2&thgr; and in‐plane &Fgr; scans as well as by cross‐sectional high‐resolution transmission electron microscopy. Four‐probe resistivity measurements show that the critical temperature of the film on LaAlO3is 78 K. The critical current density of the epitaxial layer was one order of magnitude greater than that of textured films on MgO.

ISSN:0021-8979    

DOI:10.1063/1.352834

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

A simplified mean‐field calculation of the magnetic entropy change for the Ising‐like rare‐earth magnets DyAlO3and Dy3Al5O12is performed, showing DyAlO3to be a more promising working material for the 4.2–20 K range Carnot‐type magnetic refrigerators than the conventional refrigerant Dy3Al5O12.

ISSN:0021-8979    

DOI:10.1063/1.352835

出版商:AIP    

年代:1993

数据来源: AIP