摘要:

A calorimetric technique, involving measurement of the thermal conductivity, was used to measure non‐Ohmic ac power losses in short, 0.25‐mm‐diam samples of superconducting Nb‐25% Zr and Nb‐33% Zr wire as a function of frequency, current amplitude and waveform, and temperature. The observed power losses at 4.2°K ranged from 6×10−11to 10−7W/cm. The losses depended linearly on frequency in the range 60–40 000 cps and decreased approximately asT2.5for temperaturesTin the range 2.0°–4.2°K. Peak currents from 1 to 8 A were used to determine that the power loss was a function of the peak currentImrather than the rms current and also was proportional toImn, wherenvaried from 2.6 to 4.5. These results indicate a hysteresis loss mechanism with no detectable relaxation effects for the entire frequency range covered. Models which have been proposed to account for hysteresis losses in hard superconductors are discussed. The results of this experiment are compared with earlier measurements on Nb‐Zr alloys. There is considerable disagreement between the present results and the published results of Zar in magnitude and in the frequency and current dependences of the ac power losses.

ISSN:0021-8979    

DOI:10.1063/1.1713819

出版商:AIP    

年代:1964

数据来源: AIP

摘要:

The thermalJ‐Vcharacteristic for a tunnel junction is derived in terms of a generalized theory. The resulting functional form of the equations is similar to that of Stratton; however, in the present formulation, the physical parameters of the junction appear explicitly, and their effect upon the thermal characteristic is readily appreciated. In Stratton's work, the physical constants appear in the integrand of integral that can be solved only numerically.The theory is applied to symmetric and asymmetric junctions. For the symmetric case, it is shown that, at a given temperature, the percentage changeJˆin the high‐temperature thermal component of current from the low‐temperature valueincreasesinitially with increasing voltage bias up to a maximum peak, and thereafterdecreasesrapidly. The voltage bias at which the component of thermal current maxima occurs is equal to the interfacial barrier height and, as such, permits what is probably the most accurate method of barrier height determination. Similar results are obtained for the asymmetric barrier; however, in this case,Jˆdepends upon the polarity of the voltage bias forV>&phgr;1, and twoJˆmaxima occur at voltages corresponding to the two distinct interfacial barrier heights &phgr;1and &phgr;2.

ISSN:0021-8979    

DOI:10.1063/1.1713820

出版商:AIP    

年代:1964

数据来源: AIP

摘要:

A method for measuring Hall mobility and resistivity in thin layers of semiconducting materials uses four contacts near the center of a sample that is large in comparison to the contact spacing. The measured value of the Hall coefficient is independent of the relative positions of the contacts. For resistivity measurements the contacts have to lie on a circle; the error due to a 10% deviation from this condition is 3%. If the contact spacing is110of the smallest sample dimension the Hall coefficient is accurate to 2.5% and the resistivity measurement to 5.5%.Where it is not possible to make the sample large in comparison to the contact spacing, a circular sample and a square array of contacts is proposed. Arrangements which do not fit either case but closely approach both can be treated by first using the infinite sheet method and then correcting for the finite size of the sample by the circular sheet method.These methods may be useful where it is not convenient to form either Hall bridges or contacts to the edge of the sample, as in the van der Pauw method. Measurements on epitaxially grown layers might be carried out by this method.

ISSN:0021-8979    

DOI:10.1063/1.1713821

出版商:AIP    

年代:1964

数据来源: AIP

摘要:

The several models for double injection of electrons and holes into solids are shown to fall into three groups: field‐dominated, diffusion‐dominated, and hybrid models. The current‐voltage relation for the field‐dominated models can be written out of hand, within a factor of two, using the criterion: ambipolar drift transit time of free pairs=lifetime of free pairs. Current‐voltage dependenciesJ∝Vn, withnranging from 1.5 to 3, depend on whether the material is insulating or semiconducting and the recombination monomolecular or bimolecular. In the diffusion‐dominated models the current increases indefinitely while the voltage across the body of the sample remains constant at a value 2kT/eexp (L/2LD), whereLandLDare the sample length and diffusion length, respectively. In the hybrid models, a field‐dominated current in one part of the sample is matched to a diffusion‐dominated current in the remainder of the sample. For all of the models reviewed, solutions for the current‐voltage relations are obtained within a factor of two by relatively simple physical arguments.

ISSN:0021-8979    

DOI:10.1063/1.1713822

出版商:AIP    

年代:1964

数据来源: AIP

摘要:

Al&sngbnd;SiO&sngbnd;Al&sngbnd;SiO&sngbnd;Au triodes with SiO thicknesses between 150 and 500 Å have been used to measure the potential distribution in thin oxide films before, during, and after the development of voltage‐controlled negative resistance (VCNR) in the current‐voltage characteristics. Development of VCNR in the triode is accompanied by the establishment of a high‐field region about 120 Å in thickness near the negative electrode. If triode potentials are reversed after developing conductivity, VCNR is still found in the current‐voltage (I‐V) characteristic of the triode but the potential distribution in the triode is only slightly changed. VCNR in theI‐Vcharacteristic is a high‐field phenomenon but it does not depend on field emission of electrons from the metal electrodes. Conductivity in the bulk of the insulator is Ohmic with electron mobilities ∼10−3−10−2cm2/V‐sec. The behavior of Al&sngbnd;SiO&sngbnd;Au diodes is identical to that of triodes. Electroluminescence of Al&sngbnd;SiO&sngbnd;Au diodes, which appears when conductivity is developed, is characterized by a steep rise in intensity at 1.8 V, the voltage at which electron emission into vacuum from such diodes is first detected. Both electroluminescence and electron emission provide evidence for high‐energy processes in the oxide film. A phenomenological model of conductivity and voltage‐controlled negative resistance in thin oxide films is developed in which impurity conduction is the most important conduction mechanism.

ISSN:0021-8979    

DOI:10.1063/1.1713823

出版商:AIP    

年代:1964

数据来源: AIP

摘要:

The theory is based upon the hypothesis that free charge carriers—electrons and holes—and phonons exert pressures inside a solid. Gradients of such pressures exert motive forces on the carriers. On this basis, the hole current densityIp, in the absence of a magnetic field, is assumed to beIp=&sgr;pE−&mgr;pgrad Pp−&mgr;p[open phi]gradP[open phi],where &sgr;p, &mgr;p, andPpare, respectively, the conductivity, mobility, and pressure of holes; &mgr;p&phgr;is the interaction mobility between holes and phonons;P&phgr;is phonon pressure; andEis the electrostatic field. A similar expression is obtained for electrons by exchanging the subscriptpforn. (The two mobilities associated with electrons, however, are negative.)The theory is applied to the nondegenerate semiconductor, with the assumption that the equation of the ideal gas law applies. (Thus,Pp=pkT, Pn=nkT, wherekis the Boltzmann constant,Tis temperature Kelvin, andpandnare concentrations of holes and electrons, respectively.) It is also assumed— for small currents—that deviation from the equilibrium pressures can be neglected.Assumptions concerning the phonon effect are quite general; the contribution from this source to the hole current densityIpis given byIp[open phi]=−&sgr;p(kT/e)&dgr;p grad ln T,whereeis magnitude of electronic charge. The dimensionless quantity &dgr;p, the phonon‐dragging coefficient for holes (a temperature‐ and material‐dependent parameter), is not amenable to calculation by the theory, in its present form, and must be determined experimentally. Again, a similar expression exists for electrons.

ISSN:0021-8979    

DOI:10.1063/1.1713824

出版商:AIP    

年代:1964

数据来源: AIP

摘要:

The redistribution of impurities during thermal oxidation of silicon was studied both theoretically and experimentally. Experiments with specific impurities indicate that gallium, boron, and indium deplete from silicon, while phosphorus, antimony, and arsenic pile up during thermal oxidation. It is shown that the redistribution process can be significantly influenced by the escape of impurities through the oxide layer as well as by the segregation of the impurity at the oxide‐silicon interface.

ISSN:0021-8979    

DOI:10.1063/1.1713825

出版商:AIP    

年代:1964

数据来源: AIP

摘要:

General expressions for the acoustoelectric current in the presence of external electric and magnetic fields have been derived. The Weinreich relation is shown to be valid in materials in which carriers of one sign only are present, to the extent that collision‐drag effects may be neglected. The Weinreich relation is not valid for semimetals. However, in high magnetic fields, the acoustoelectric current and field in semimetals are proportional to the attenuation. The acoustoelectric field is then in the directionq×H, whereqis the wave vector, andHthe magnetic field. The acoustoelectric current reinforces the original direct current under amplifying conditions, in agreement with observations of anomalous magnetoresistance in Bi.

ISSN:0021-8979    

DOI:10.1063/1.1713826

出版商:AIP    

年代:1964

数据来源: AIP

摘要:

The energy dependence of radiation damage in silicon for proton energies in the range 1.35 to 130 MeV has been measured by observing the degradation of the bulk minority carrier diffusion length in silicon solar cells. Variability in proton flux determination at four different accelerators was minimized by employing prebombarded solar cells with known minority carrier diffusion lengths as calibrated solid‐state ionization chambers. Where beam intensity measurement comparisons with Faraday cups could be made, agreement to better than 5% was obtained.The quantity characterizing the damage rate is the rate of change of the inverse square diffusion length with fluxK≡d(1/L2)/d&PHgr;. The 1‐&OHgr;‐cmp‐type silicon degraded, on the average at a rate six times less rapid than 1‐&OHgr;‐cmntype, independent of energy. Room temperature annealing gave 30% to 50% decrease inKwhenever the diffusion length was measured during and after irradiation. The energy variation ofKagrees with the variation predicted by Rutherford scattering below 8 MeV, but decreases less rapidly at higher energies.The measured diffusion lengths increased with excess carrier densitynfrom 2% per decade atn=109cm−3to 20% per decade atn=1014cm−3. The reported results, obtained at low excess carrier density, can be used to predict solar cell degradation under conditions of outer space illumination if the appropriate excess carrier density is used. Failure to take into account the diffusion length variation will result in an underestimate of the solar cell output of less than 7%.

ISSN:0021-8979    

DOI:10.1063/1.1713827

出版商:AIP    

年代:1964

数据来源: AIP

摘要:

The electron capture cross section of sensitizing centers for photoconductivity has been measured as a function of temperature between 77° and 350°K in CdS, Cd(SSe), CdSe, GaAs, and InP crystals. The value of the cross section is obtained from the measurement of the minimum number of quenching photons per second required to initiate optical quenching, at a temperature below that at which thermal quenching occurs. Forty‐one determinations of cross‐section on nine different crystalline samples yield values between 10−20and 10−22cm2with only slight temperature dependence. A consideration of the various models to account for such small capture cross sections without appreciable temperature dependence suggests that the cross section is associated with radiative capture by a neutral center.

ISSN:0021-8979    

DOI:10.1063/1.1713828

出版商:AIP    

年代:1964

数据来源: AIP