摘要:

Dramatic enhancements of over300×in the room temperature photoluminescence signal obtained from high purity GaAs epitaxial layers were recorded after a brief heat treatment in tertiarybutylphosphine vapor. Low temperature photoluminescence spectra indicate that, unlike other passivation techniques, the surface layer formed during this simple treatment does not induce any appreciable strain on the underlying epilayer. The increases in photoluminescence intensity are indicative of a reduction in surface recombination brought about by the formation of a very thin GaP layer that protects against surface oxidation. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.118426

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Self-organized CdSe/ZnSe quantum dots (QDs) have been fabricated on GaAs (110) crystal surfaces, which were obtained by cleaving GaAs (100) wafers in ultrahigh vacuum. CdSe showed a conventional Stranski–Krastanow growth mode on the ZnSe (110) lower cladding layer, whose surfaces are atomically flat. The wetting layers, which are compose of quantum wells with well widths of 1, 2, and 3 monomolecular layers, showed sharp photoluminescence (PL). The fabricated CdSe QDs showed intense green PL spectra, whose peak is located at 2.192 eV, with a linewidth of 0.24 eV. The state filling effect in CdSe QDs was also observed by employing excitation power dependence of the PL intensity. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.118427

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We measure the transient enhanced diffusion of shallow molecular-beam-epitaxy grown marker layers of Sb and B due to deep MeVSi+ion implants at very high doses(≈1016 cm−2).We expect the near-surface region of these implants to be vacancy rich, and we observe transient enhanced diffusion of Sb (the classic vacancy diffuser). The large enhancements imply a significant vacancy supersaturation (≈700at 740 °C). Double implantation of the high-dose MeV Si followed by a shallow (40 keV) Si implant and annealing produces a greatly reduced number of {311} defects compared to a 40 keV implant into virgin Si, again consistent with a vacancy-rich region in the near-surface region of an MeV implant. However, the shallow B marker layers also show transient enhanced diffusion for the same MeV implant under similar annealing conditions, implying that an interstitial supersaturation is present at the same time. We discuss possible mechanisms for a simultaneous supersaturation of both types of point defects. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.119150

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Electronic properties of partially relaxedInxGa1−xAs/GaAs multiple quantum well (MQW) structures are investigated using capacitance–voltage (C–V) profiling and deep level transient spectroscopy (DLTS). As the In composition becomes large, the depletion of carriers confined in QWs and the concentration of dislocation-related deep traps are increased. The carrier depletion is observed to occur predominantly in the QWs adjacent to the bottom layer. This depletion is believed to be due to electron capture at the acceptor-like misfit dislocation-related traps. Our results thus show that theC–Vand DLTS measurements, combined with the numerical simulation ofC–Vprofiles, can be used to study the influence of nonuniformly distributed misfit dislocations on the carrier distribution in MQW structures. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.118428

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

A model to explain the hydrogen desorption kinetics in SiGe alloys is presented. This is an extension of a previous desorption model of hydrogen from Si, that considers the presence of three dimer types in the surface in which hydrogen atoms tend to pair before the desorption reaction. Surface diffusion is included in the model. The comparison with experimental results shows that desorption is a diffusion limited process. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.118429

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

A high temperature superconducting YBa2Cu3Oyarray of five Josephson junctions designed with additional coupling lines has been developed to demonstrate the effects of frequency locking and impedance matching for applications such as oscillators, mixers, and detectors. The Josephson self-radiation power was directly detected by a superheterodyne receiver, and Shapiro steps were also measured. The Josephson self-radiation properties reveal good quality of phase locking and microwave coupling with external circuits. The maximum self-radiation power of our array is about 50 pW which is several ten times higher than that of a single Josephson junction, and its peak point exactly satisfies the Josephson current-voltage relation. The Shapiro-step measurements show that the behavior of current-voltage curve depends on the effective inductance of coupling lines which affects the total impedance of Josephson junction array and microwave coupling. The Josephson oscillation frequency was obtained up to about 880 GHz which is 73&percent; of the maximum available frequency calculated from the characteristic voltage of the Josephson junctions. Experimental results show that this type of Josephson junction array can improve the Josephson self-radiation power and increase the maximum detectable frequency. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.118430

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We have studied the microwave properties of 0.4 &mgr;m thickYBa2Cu3O7−x(YBCO) films on polycrystalline substrates with ion-beam-assisted-deposited yttria-stabilized zirconia buffer layers using a parallel-plate resonator technique at 10 GHz. The YBCO films with similar in-plane texture grown on both forsterite and Ni-based alloy substrates show similar microwave properties. We measure low-power surface resistanceRsvalues of about 0.5 m&OHgr; at 76 K and 0.15 m&OHgr; at 4 K for films with an in-plane mosaic spread of about 7°. Single-tone power-dependence measurements show that the surface resistance and the surface reactance increase linearly and by the same amount with increasing microwave field level. At intermediate power levels, the intermodulation measurements show odd-order intermodulation products that increase quadratically with two-tone input power. These results indicate a hysteretic vortex penetration mechanism in the weak links as the most plausible source of the observed nonlinearities in these films. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.118431

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We have measured the noise performance and gain bandwidth of 35 Å thin NbN hot-electron mixers integrated with spiral antennas on silicon substrate lenses at 620 GHz. The best double-sideband receiver noise temperature is less than 1300 K with a 3 dB bandwidth of ≈5 GHz. The gain bandwidth is 3.2 GHz. The mixer output noise dominated by thermal fluctuations is 50 K, and the intrinsic conversion gain is about −12 dB. Without mismatch losses and excluding the loss from the beamsplitter, we expect to achieve a receiver noise temperature of less than 700 K. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.119143

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

A giant magnetocaloric effect(&Dgr;Smag)has been discovered in theGd5(SixGe1−x)4pseudobinary alloys, wherex⩽0.5.For the temperature range between∼50and∼280 Kit exceeds the reversible (with respect to alternating magnetic field)&Dgr;Smagfor any known magnetic refrigerant material at the corresponding Curie temperature by a factor of 2–10. The two most striking features of this alloy system are: (1) the first order phase transformation, which brings about the large&Dgr;SmaginGd5(SixGe1−x)4,is reversible with respect to alternating magnetic field, i.e., the giant magnetocaloric effect can be utilized in an active magnetic regenerator magnetic refrigerator; and (2) the ordering temperature is tunable from∼30to∼276 Kby adjusting the Si:Ge ratio without losing the giant magnetic entropy change. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.119206

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The spatial dependence of the magnetic moment perturbation near the (1-10)-Fe/Co interface was derived from hyperfine fields determined by perturbed angular correlation. The amplitude of the moment perturbation decays exponentially with the distance to the interface. The moment perturbation itself is modulated by a sine function of the distancedto the interface&Dgr;&mgr;=A*exp(−p*|d|)*sin(−k*d). Between 90 K and 570 K, we observe that the amplitude and the penetration depth of the perturbation as well as the wave vector of the modulation are essentially constant within the accuracy of the values. In this temperature region the average values for the parameters determining the exact moment perturbation areA=1.03&mgr;B,p=2.25×109m andk=1.45×1010 m−1whendis defined positive at the Co side of the interface.©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.119144

出版商:AIP    

年代:1997

数据来源: AIP