摘要:

A six‐electrode cell measures both a horizontal and vertical resistivity on a single deformable sample under compacting load. The similar effects of anisotropy and sample thickness on the ratio of two voltages in the cell allow a determination of the anisotropy coefficient. The geometric mean resistivity is obtained using a cell constant appropriate to the electrically determined product of the anisotropy coefficient and sample thickness. Clay and shale materials have ratios of vertical to horizontal resistivity of from near unity to 25 to 1.

ISSN:0021-8979    

DOI:10.1063/1.1709132

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

The Hall coefficients of selectedn‐type GaSb‐InSb alloys have been measured in the range 300° to 800°K. The temperature dependence of the Hall coefficient showed the presence of two bands, and data were analyzed using a two‐band model. The energy separation of the two conduction‐band minima was found to increase, with increasing InSb concentration, from 0.034 to 0.52 eV in the composition range investigated. The temperature dependence of this separation was found to be positive for GaSb and negative for the alloys ranging between +1.8 to −2.0×10−4eV/°K.

ISSN:0021-8979    

DOI:10.1063/1.1709133

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

Photoluminescence measurements were made of closely compensated,n‐type GaAs grown by the horizontal Bridgman method. The ratio of Ge donors to Ge acceptors is estimated to be ∼1.25. At 77°K (n≅3× 1017cm−3) emission bands are observed at 1.51, 1.49, and 1.22 eV. The second band is nearly comparable in intensity to the first in these materials and is ascribed to a recombination process involving a shallow Ge acceptor level. These data suggest that this level is located 0.02–0.03 eV above the valence band. The band at 1.22 eV is considerably more intense than the other bands. Evidence is presented suggesting that this band is due to a shallow donor to deep acceptor radiative transition. The shallow donor is probably Ge. The deep acceptor level is approximately 0.2 eV above the valence band and may involve a lattice defect particularly prominent in melt‐grown GaAs. The low‐energy emission band has been correlated with an absorption peak. On the basis of the absorption data, the deep acceptor concentration is roughly estimated to be of the order of 1016cm−3.

ISSN:0021-8979    

DOI:10.1063/1.1709134

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

Electroluminescence was observed in ZnTe devices fabricated from crystals in which oxygen was incorporated. Main emission peaks were located at 6960 Å at 293°K and 6580 Å at 77°K, and external quantum efficiencies of 10−3–10−4were obtained at room temperature. The emission from these devices is considered to result from recombinations taking place at oxygen centers which appear to be located approximately 0.4 eV from the band edge. Improvements in the emission properties of these devices over similar diodes fabricated from undoped material are described.

ISSN:0021-8979    

DOI:10.1063/1.1709135

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

Niobium films with superconducting transition temperatures between 8.2° and 9.1°K have been deposited by dc diode sputtering. The results are shown to be due to the reduction of the film impurity content by extensive presputtering and high substrate temperatures.

ISSN:0021-8979    

DOI:10.1063/1.1709136

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

The breakdown of gases under the influence of a laser beam is analyzed. Classical diffusion theory is taken as a model, with electrons accelerated by inverse bremsstrahlung until they have sufficient energy to ionize neutral gas atoms. Both diffusion and recombination are included as losses.For the rare gases in the range below atmospheric pressure it is found that the relation between the laser pulse duration and the plasma growth time is the primary factor which determines the breakdown threshold. The losses play roles of varying importance depending on gas, pressure, and geometry. The initial electrons are generally assumed to have come from multiphoton ionization of impurities, although multiphoton ionization of the gas itself becomes a factor at sufficiently low pressures (high photon fluxes).A number of experimental results is presented. These are used to justify some of the theoretical assumptions and to corroborate the results of the theory. The agreement is good.

ISSN:0021-8979    

DOI:10.1063/1.1709137

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

In nickel‐iron films thicker than about 100 nm (1000 Å), fast‐rising field pulses along the hard anisotropy axis lead to a new kind of wall displacement called ``wall streaming,'' which does not require any field component parallel to the wall necessary for all other wall motion processes. The walls are displaced with a very regular wall step width per pulse which strongly depends on the strength of the pulse field and on the pulse rise and fall times, but not on the pulse duration. The direction of wall motion reverses if the pulse polarity is reversed. During the application of a sequence of uniform pulses, the direction of wall motion may also reverse, beginning at one end of the wall, with a reversing line (interpreted as being a Ne´el line moving along the wall. The phenomenon is explained as a consequence of the gyromagnetic behavior of the magnetization in the Bloch walls. A detailed theory is presented, in which the intrinsic spin damping and the film inhomogeneity (characterizable by the coercivity) are to be taken into account. Wall streaming may contribute to a destruction of the information stored in magnetic films thicker than 100 nm (e.g., in plated‐wire memories) as soon as fast‐rising (tr≲20 nsec) pulses are applied.

ISSN:0021-8979    

DOI:10.1063/1.1709138

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

Annealing in zinc or sulfur vapor introduces major changes in the photoelectronic properties of ZnS single crystals. Insulating insensitive crystals of ZnS were annealed for various periods of time from 20 min to 6 days at 891°C in a saturated zinc vapor. Annealing increases the dark conductivity by at least eight orders of magnitude, the photosensitivity by over three orders of magnitude, and markedly affects photoluminescence emission. The effects of annealing in zinc are reversible by subsequent annealing in sulfur vapor. Optical quenching data show that the high photosensitivity in the zinc‐annealed crystals is associated with sensitizing centers lying 1.2 eV above the valence band with an electron‐capture cross section of about 10−21cm2. The photosensitivity decreases rapidly with decreasing temperature below 200°K, whether excitation is by intrinsic ultraviolet or extrinsic infrared, because of the effects of a high density of shallow electron traps. The principle effect of annealing appears to be in the variation of the Fermi‐level position in the crystal.

ISSN:0021-8979    

DOI:10.1063/1.1709139

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

The electrical effects occurring during freezing of dilute aqueous solutions have been studied using NH4OH and NH4Cl solutions. The freezing potentials depend on the concentration of the solution and the rate of growth of the solid phase. This effect is an impurity effect and does not appear in pure material. The phenomenon can be explained by a model in which the impurity rejected by the growing solid into the solution ionizes, one kind of ion being adsorbed on the solid surface at the interface and the other kind diffusing into the liquid. The impurity ion adsorbed on the surface moves with the surface and is not incorporated into the solid phase. This effect is confined to a narrow range of concentration of the solutions.

ISSN:0021-8979    

DOI:10.1063/1.1709140

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

Electrical transport studies inp‐type ZnTe have confirmed that in the temperature range of about 80° to 500°K the hole mobility is principally limited by LO phonon scattering. An effective mass ratio of 0.6 gives the best fit to the experimental data. The highest mobility, 6500 cm2/V·sec at 35°K, was observed in a crystal with an active defect center concentration of 2×1015cm−3. The ionization energy of the first charge state of a native acceptor, believed to be a Zn vacancy, was found to be ≥0.057±0.002 eV. Besides acting as shallow acceptor defects in ZnTe, the elements Li, Na, and P were found to promote the incorporation of substantial concentrations of native defects. High concentrations of Li, under excess Zn firing conditions, were observed to lead to highly compensated, low‐mobility material, suggestive of self‐compensation of the Li dopant.

ISSN:0021-8979    

DOI:10.1063/1.1709141

出版商:AIP    

年代:1967

数据来源: AIP