摘要:

A recently identified relationship between the probability of collection of a photogenerated carrier in a solar cell and the dark minority-carrier concentration at the point of generation is generalized to three-dimensional geometries with arbitrary doping profile and variable band gap including abrupt compositional changes, grain boundaries, and floating junctions. The proof of the resulting relationship is simpler and more transparent than in earlier work with more restricted geometries. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.364108

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Anomalous non-Gaussian effects appear in the resistance fluctuations of a macroscopic sample of the colossal magnetoresistive material La2/3Ca1/3MnO3. Individual resistance switches are frequently resolved. The results indicate the presence of highly inhomogeneous hopping resistance among magnetic domains in this partially disordered material ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.363844

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The electrical results of rf sputtered hydrogenated amorphous silicon carbide (a-Si1−xCx:H) films prepared under different sputtering conditions are presented. It was found that hopping and Poole–Frenkel effects are the conduction mechanisms for low and high applied fields, respectively. From the capacitance versus voltage measurements, the fixed charge density (Qf) and the interface trapped charge density (Dit) were found to be in the range of 5.5–6.81×1010cm−2and 5–13×1011eV−1 cm−2, respectively.Ditdecreases with either an increase in the total sputtering pressure, the partial hydrogen pressure, or the substrate temperature, but increases with an increase in the rf sputtering power. The decrease inDitwas found to be closely related to the increase in the number of silicon–hydrogen bonds. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.363845

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

A new method using the Hall technique to determine the change in surface layer thickness of doped semiconductors is presented. An equation to calculate the semiconductor thickness change has been determined by comparing the difference in Hall measured sheet carrier concentration and mobility before and after a change in surface layer thickness. Experiments were conducted using a wet chemical digital etch to removen-type GaAs surface layers having an incremental etch depth control of approximately 15 Å in thickness, and the resulting thickness changes were calculated by the Hall technique and measured with a mechanical profilometer. This Hall measurement technique was able to measure changes in surface layer thickness of less than 100 Å, and the accuracy of this new technique compared favorably with mechanical profilometer measurements. The new Hall technique method provides accurate measurements of minute thickness changes, and is more accurate than mechanical profilometers for thickness changes less than 150 Å.©1997 American Institute of Physics

ISSN:0021-8979    

DOI:10.1063/1.363846

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We predict a spatially varying mode population to appear in a ballistic quantum channel formed in the two-dimensional electron gas of a gated GaAs/AlGaAs heterostructure due to pumping by a THz field. If a resonant coupling between two modes is suddenly switched on at the entrance, Rabi oscillations in the mode population will arise. We propose to use an array of gates in order to simulate a moving quantum point contact for detecting mode population oscillations since they discriminate between different modes. By consecutively activating them we expect to see both photovoltaic effects and photoconductive effects that can easily be distinguished from noise. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.364106

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We report a modification by thin silicon nitride intralayers of the Au/n-GaAs(100) Schottky barrier height. Thin intralayers were obtained by nitridation of evaporated Si films on decapped GaAs substrates in an argon–nitrogen mixture plasma. The nitridation was performed at a beam energy <40 eV, with 573 K sample temperature. Gold was deposited to studyin situthe Schottky barrier formation process with x-ray photoelectron spectroscopy. Internal photoemission spectroscopy and current–voltage measurements were used to evaluate the barrier modification on fully formed interfaces. Such a modification was analyzed in terms of theoretical calculations of the dipole created by the substrate–intralayer bonds. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.363847

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Thermally stable, low-resistance ohmic contacts to GaAs (Si-doped,n=1.6–1.8×1018cm−3) were formed using PdIn metallization sputter-deposited from an alloy target. Average specific contact resistances (&rgr;c) in the 10−6&OHgr; cm2range were reached upon annealing at 600 °C or higher. Contacts annealed under the optimum condition of 850 °C for 15 s exhibited an average&rgr;cof 2.5×10−6&OHgr; cm2. The 100 h of thermal aging at 400 or 500 °C increased their average&rgr;cto 3.0×10−6and 1.0×10−5&OHgr; cm2, respectively. The ohmic behavior of the annealed contacts was ascribed to the exchange of In and Ga atoms between the metallization and the semiconductor and the concomitant formation of InxGa1−xAs, whose presence at the contact interface was confirmed using cross-sectional transmission electron microscopy. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.363848

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

A theoretical and experimental investigation is made of the surface impedance of dc current biased high-quality epitaxial YBa2Cu3O7−&dgr;thin films using a coplanar resonator technique. The isotropic Ginzburg-Landau theory and a current-dependent coupled-grain model are used to model the resonant frequency shift and the change in unloaded quality factorQ0due to the bias current. Good quantitative agreement is obtained between the two models and the measured resonant frequency shift. The change inQ0, determined from measurements, can be explained by the coupled-grain model. The Ginzburg-Landau theory predicts a change inQ0which is several times less than given by measurements. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.364109

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The experimental and numerical study of parallel one-dimensional arrays consisting of double-layer stacked small Josephson tunnel junctions is reported. In addition to several features already known for classic single-layer arrays, we find a new resonant state which corresponds to the locking of the fluxon oscillations to a frequency of small-amplitude oscillations of the superconducting phase in middle islands of small stacks. Numerical simulations of a simplified circuit agree well with experiments and confirm the suggested qualitative mechanism. In these experiments we find no indication for the so-called multiple-fluxon propagation in double-junction arrays.©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.364110

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The use of the intrinsic Josephson effect in layered high-Tcsuperconductors for parametric amplification of a signal in the presence of a strong pump radiation is investigated. Model calculations are performed both for thin films and massive material with a surface parallel to the c direction assuming normal incidence of the radiation with electric field parallel in c direction. In both cases a positive signal gain is obtained in a limited range of frequencies and pump power. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.364112

出版商:AIP    

年代:1997

数据来源: AIP