摘要:

The current‐voltage curves for a germanium diode at 4.2 K are calculated by two methods and the calculations compared with experimental data. The diode is modeled by a one‐dimensional, semiclassical semiconductor. The nonlinear transport differential equations are solved by numerical integration and by evaluating parametric equations for the voltage and current.

ISSN:0021-8979    

DOI:10.1063/1.353394

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

The proposed sequential tunneling model predicts that the negative differential resistance in a double‐barrier diode (DBD) can exist independent of a resonant Fabry–Perot effect. The proof is based on the existence of quasi‐two‐dimensional states for electrons in the quantum well. However, we find that existence of the quasi‐two‐dimensional states depends on a Fabry–Perot resonance. Therefore, if coherence of electrons in the quantum well is completely lost, then the quasi‐two‐dimensional states will also disappear. We find that the damped Fabry–Perot model can provide a unified formula for electron transport in the DBD from pure coherent tunneling to pure incoherent tunneling. In the latter case, the negative differential resistance disappears.

ISSN:0021-8979    

DOI:10.1063/1.353395

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

We have measured the Josephson radiation emitted at millimeter‐wave frequencies by a long Josephson junction dc‐current biased on Fiske steps of the current‐voltage characteristic. Our measurements demonstrate that differences between dynamic excitation generating Fiske steps and fluxon oscillations giving rise to zero‐field steps in long junctions may exist. The radiation, whose maximum measured frequency is 240 GHz, is generated by an in‐line junction and detected on a chip by a small planar tunnel junction. From measurements of Shapiro steps amplitude and photon‐assisted tunneling steps we find that the coupled radiation has a power tunability of 350 nW and the maximum coupled power is 20 nW in a 30‐&OHgr; normal‐state resistance tunnel junction.

ISSN:0021-8979    

DOI:10.1063/1.353396

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

We report a novel measurement technique for the wide‐band determination of the frequency response of photodetectors. It is based upon the accurate measurement of the photocurrent noise spectra under illumination with a light‐emitting diode. The high sensitivity of −200 dBm/Hz within a frequency regime from 10 MHz to 1.6 GHz renders it particularly attractive for investigating the response behavior at low optical input levels and for characterizing frequency‐dependent gain phenomena. The practical potential of the method is illustrated by applying it to various types of InGaAs‐based photodetectors (p‐i‐nand avalanche photodiodes and metal‐semiconductor‐metal photodetectors).

ISSN:0021-8979    

DOI:10.1063/1.353397

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

The acoustic field inside a surface acoustic wave device was studied by means of double‐crystal x‐ray diffraction. Angular satellites in the diffraction pattern were observed due to the coherent scattering on the acoustic superlattice. Satellite dynamics allows determination of the acoustic wave amplitude. Due to the sensitivity of x‐ray diffraction to the direction of atomic displacements, the amplitude of different polarization components in the Rayleigh wave can be obtained.

ISSN:0021-8979    

DOI:10.1063/1.353398

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

We have used a mono‐ion oscillator to demonstrate the usefulness of a spectroscopic technique for achieving high‐resolution frequency measurements in the presence of anharmonicity. The technique uses a noise‐free parametric process to amplify a weakly pre‐excited oscillator that allows one to reduce anharmonic frequency shift and at the same time to detect the resonance signal with large amplitude. In our initial experiments using the parametric process, 100 times narrower spectral lines have been obtained. The technique is potentially useful in such high‐precision experiments as the electrong‐2 measurement and the ion mass spectroscopy in Penning traps. The possibility of using the parametric process to detect then=0→n=1 transition of the cyclotron motion in geonium is also discussed.

ISSN:0021-8979    

DOI:10.1063/1.353399

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

We report results of an investigation of interdiffusion in GaAs/Ga0.82In0.18As strained single quantum wells. Wells of width 12–100 A˚, grown by organometallic vapor phase epitaxy, were subjected to 10 s rapid thermal anneals of 830–950 °C, and shifts in the electron‐to‐heavy‐hole transition energies were detected by 4 K photoluminescence. We employed a powerful computer model to relate postdiffusion well shape to changes in photoluminescence energies, enabling estimation of diffusivity. Interdiffusion rates of 1×10−16–2×10−14cm2/s and activation energies of 3.1–3.8 eV were obtained.

ISSN:0021-8979    

DOI:10.1063/1.353376

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

This communication reports a relatively simple technique to measure the alternating current (ac) loss in superconductors and also determines the effect of electromagnetic radiation on the measurement of ac losses. The interaction of the electromagnetic radiation with the superconductor was found to increase the ac loss. The enhancement of ac loss has been explained on the basis of generation of additional charge carriers and their interaction with the lattice.

ISSN:0021-8979    

DOI:10.1063/1.353377

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

At least three quantities have been referred to as ‘‘activation energies’’ in association with fits to metastable defect kinetics in hydrogenated amorphous silicon. Most commonly cited isE&tgr;, the activation energy determined from stretched‐exponential fits to kinetics data measured over a range of temperatures. The stretched exponential can also be written in terms of a rate constant,K, which has been reported as being thermally activated. In addition, a stretched‐exponential model describing defect kinetics includes an energy,E2, in its rate equation. In this article, we clarify the interpretations ofE&tgr;,EK, andE2, and discuss the possible physical significance ofE&tgr;.

ISSN:0021-8979    

DOI:10.1063/1.353378

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

An explanation of the interfacet migration behavior observed in molecular beam epitaxical growth of GaAs and AlGaAs on patterned GaAs(100) substrates is presented on the basis of the nature of the ledge–ledge interaction.

ISSN:0021-8979    

DOI:10.1063/1.353353

出版商:AIP    

年代:1993

数据来源: AIP