摘要:

Transmission electron microscopy has been used to study defects in as‐grown MgO single crystals and in crystals which had undergone high‐temperature electrical conduction for long periods of time. Besides dislocation loops of (a/2⟨110⟩) Burgers vectors and precipitates, a new type of defect, dislocation loops of &agr;⟨100⟩ Burgers vectors lying in {100} planes, has been observed in electric‐field‐treated specimens. The nature of both (a/2) ⟨110⟩ anda⟨100⟩ loops was determined to be vacancy type. The relation of this microstructure to the observed increase in electrical conductivity, which ultimately results in thermal‐electric breakdown of the samples, is discussed.

ISSN:0021-8979    

DOI:10.1063/1.324565

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

Recently, we reported on the development of a new thin‐film organic solar cell with an AM1 sunlight efficiency of about 0.7% for large area devices (∼1 cm2). This relatively high‐efficiency MIS‐Schottky barrier‐type cell was based on merocyanine type photosensitizing dyes. In this paper we present additional experimental results and develop a comprehensive theoretical model to explain the observed photovoltaic properties. The model incorporates the generation, transport, and surface dissociation of excitons and field‐dependent quantum efficiency. The low fill factor of 0.3 was attributed mainly to the field dependence of quantum efficiency. An exciton diffusion length of 60 A˚ was determined by analyzing the short‐circuit photocurrent action spectra using the theoretical model developed. The diffusion potentials for metal/merocyanine Schottky barrier cells for six different metals were determined byC‐Vmeasurements; the diffusion potential increases with decreasing work function. As solar cells, these devices have higher efficiencies when there is a very thin interfacial oxide layer between the barrier forming metal and merocyanine.

ISSN:0021-8979    

DOI:10.1063/1.324566

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

Transverse 1/fnoise in approximately 2‐&mgr;m‐thick InSb thin films is investigated experimentally at room temperature. Linear dependence of noise voltage on dc bias current is shown quantitatively. The noise intensity is inversely proportional to the number of conduction electrons in the bulk. The temperature rise of specimens due to Joule heating does not affect the noise intensity coefficient. The coefficient differs from sample to sample, which is reduced by the heat treatment of specimens, but is independent of the doped impurity concentration. As a result, the signal‐to‐noise ratio of related Hall elements is formulated for the first time for audio magnetic heads applications. The signal‐to‐noise ratio is nearly 80 dB for a 10‐G magnetic field in the audio frequency range.

ISSN:0021-8979    

DOI:10.1063/1.324567

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

Electron trapping by neutral trap centers in SiO2was studied at 77 K and at room temperature, usingn‐channel silicon‐gate IGFET structures. The electrons were injected in the dark using the forward‐bias pulsed injection method. The results show that electron trapping by the neutral centers was one to two orders of magnitude more efficient at 77 K than at room temperature; which may be compared with the previously reported electron trapping by Coulomb‐attractive centers where the capture cross sections at room temperature and at 77 K were about the same. For injected electron concentrations of less than 1016cm−2, more than 90% of the electron trapping at 77 K was due to shallow‐level centers where the captured electrons were thermally reemitted as the samples were warmed to room temperature. The concentrations of these shallow‐level traps in dry, wet, and HCl oxides were about the same, regardless of whether the aluminum evaporation was by electron‐beam or by rf heating in a tantalum boat. The capture cross section of these traps at 77 K was estimated to be about 10−15cm2atEox=1×106V/cm, decreasing slowly with increases in the oxide field. Thermally stimulated reemission measurements were made by monitoring the gate voltage shifts at constant channel conductance. Analyses of the results indicated a broad energy distribution for these shallow‐level traps, with a peak at 300±50 meV below the conduction‐band edge of SiO2and a half‐width of about 200 meV. A small portion of the enhanced trapping at 77 K was attributable to deep‐level centers where the captured electrons were not thermally reemitted at room temperature.

ISSN:0021-8979    

DOI:10.1063/1.324568

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

The formation of the potential barrier at the metal‐silicon contact has been investigated. Special emphasis has been given to the study of aging of gold–n‐type‐silicon Schottky diodes. The behavior of the electrical properties as a function of time of exposure to air has been studied, showing that the increase of the barrier height, from 0.5–0.6 eV up to the typical 0.8‐eV value is related to the diffusion of oxygen (or water vapor) from the ambient through the metal contact and its accumulation at the interface. In addition, preliminary results onp‐type silicon are reported. A phenomenological model based on the behavior of oxygen with respect to the metal involved is proposed to describe the aging for any metal deposited onn‐ orp‐type silicon.

ISSN:0021-8979    

DOI:10.1063/1.324569

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

A study of a new type varactor diode which consists of a semiconductor multilayer structure has been performed. It is shown that such a varactor diode has much stronger nonlinearity in capacitance variation with applied bias voltage than does the conventional varactor due to the two‐dimensional expansion of the depletion region. First, the internal behaviors of this diode are investigated in detail by two‐dimensional computer simulation. Based on the physical insight obtained by the simulation, an approximate analytical expression for the voltage dependence of capacitance is derived for the purpose of practical design. Then, the proposed structure has been experimentally made from Si, whose capacitance‐voltage characteristics are compared with those of the conventional structure made from the same material. Those results substantiate the theoretical predictions.

ISSN:0021-8979    

DOI:10.1063/1.324570

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

Multifilament conductors have been fabricated using niobium tubes with a sheathed tin‐copper alloy inside and pure copper matrix outside. These composites have good workability, cold drawn without any intermediate heat treatment. Reactions and their effect upon superconducting properties have been checked for temperatures in the 625–800 °C range and various inner filament sizes ranging from 18 to 1154 &mgr;m. The Nb3Sn layer thickness grows ast0.8in most of the reaction time, which cannot be explained by an ordinary diffusion process. The pinning force is found to be inversely proportional to the square root of the grain size measured through a fractographic technique in the 0.1–0.3‐&mgr;m range. Also, the activation energy of the Cu/Sn‐Cu diffusion couple is obtained as 47 kcal/mol from the reaction‐temperature–time relation. These results have been discussed and compared with others.

ISSN:0021-8979    

DOI:10.1063/1.324571

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

Films of copper molybdenum sulfide were produced by coevaporation. Those that were superconducting contained only the ternary compound and free molybdenum. The range of copper content in the ternary compound was as large as that in polycrystalline material, that is, it includes either phase alone, or a mixture of the two phases of this material. This is in contrast with sputtered materials where copper concentration has been limited to a narrower range. The upper critical field and the critical current were measured as functions of external magnetic field, and found to be similar to those of sputtered copper molybdenum sulfide, when the comparison was made for samples having the same amount of copper.

ISSN:0021-8979    

DOI:10.1063/1.324572

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

Cu‐Nb wire composites with 0.105, 0.148, and 0.182 volume fraction of Nb filaments were producedinsituand their mechanical properties measured as a function of filament size and interfilament spacing. The yield stress and the ultimate tensile strength increased with both niobium volume fraction and overall composite reduction. At room temperature, the ultimate tensile strength of the Cu–18.2 vol% Nb composite reduced by 99.999% in cross‐sectional area (100–200 A˚ filament thickness) reached the value of 2230 MN/m2(323 ksi) and further increased to 2850 MN/m2(413 ksi) when measured at 77 °K. These values are higher by a factor of 4 than the values predicted by the rule of mixtures based on the highest reported strength of both niobium and copper. The composite strength is as high as that of the best copper whiskers and is shown to closely approach the theoretical strength of the material. The anomalous increase in strength despite the low volume fraction of reinforcing filaments suggests that the filaments act primarily as barriers to the motion of matrix dislocations and that the strength of the filamentary material is only of secondary importance. This hypothesis is supported by microstructural obsevations (transmission and scanning electron microscopy) which reveal the deformation modes during composite fabrication and mechanical testing. The excellent transport properties (in both the normal and superconducting state) make these composites attractive as conductors for high‐stress applications.

ISSN:0021-8979    

DOI:10.1063/1.324573

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

Thermally grown native oxides of indium have the reputation of being rather poor‐quality tunneling barriers when indium is used as the base electrode. We have developed a simple technique in which a freshly evaporated indium film is allowed to oxidize in the presence of acetic‐acid vapor prior to the deposition of the lead counterelectrode. These easily reproduced tunnel junctions are of extremely high quality with Josephson critical current densities as high as 5000 A/cm2. Auger, electron energy loss, and ellipsometry studies reveal that there is a thinner and more uniform oxide coverage on the acid‐oxidized films when compared to air‐oxidized films. The absence of a pronounced Auger carbon peak on the tunnel junction samples, together with infrared evidence for acetate ion formation on indium samples exposed to significantly higher partial pressures of acetic‐acid vapor, suggest that there is an absorption/desorption process in which a submonolayer amount of ionized acetic acid serves as a structural relaxation catalyst at oxide sites which are at higher energy than would occur in a uniform lattice.

ISSN:0021-8979    

DOI:10.1063/1.324574

出版商:AIP    

年代:1978

数据来源: AIP