摘要:

Two distinct processes are suggested for the formation ofp‐njunctions in crystal platelets of GaP grown from Ga solution doped with Zn, Te, and O, over wide ranges of composition and growth conditions. In each growth melt, about one half of thep‐type crystals contain a shallown‐type surface layer, ∼2 &mgr; in thickness, formed by out‐diffusion of Zn after growth. Thesep‐njunctions have relatively high (>10−3) external electroluminescence quantum efficiencies at room temperature. The remainingp‐type crystals contain deeper, less efficient junctions, built into the crystals by impurity segregation effects during growth. The efficiencies ofp‐njunctions degrade with the heat treatment at 600°C used to alloy the Ohmic contacts. The extent of degradation correlates with the dislocation density and is ascribed to precipitation. The precipitates nucleate preferentially in the junction plane and grow with subsequent heat treatment.

ISSN:0021-8979    

DOI:10.1063/1.1709936

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

The elastic properties of a synthetic single‐crystal spinel with a composition of MgO·2.6Al2O3have been determined at 25°C and up to 2 kbar by measuring propagational velocities of ultrasonic waves using the method of pulse superposition. The isotropic moduli and Poisson's ratio were computed from the single‐crystal values using the Voigt‐Reuss‐Hill approximation.Values of the adiabatic elastic moduli at 1 bar and 2 kbar and at 25°C arec11c12c441bar2985.71537.21575.8(kbar)2kbar2995.51545.01577.5(kbar).The adiabatic bulk modulus was computed to be 2019.9 kbar, and the pressure derivative of the adiabatic bulk modulus was found to be 4.18.

ISSN:0021-8979    

DOI:10.1063/1.1709937

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

The dynamic Young's moduliEof molded films of a polyethylene and a polypropylene were found to decrease with increasing thicknesst. An upper limit ofEappears to exist when the film thickness is reduced to less than 1 mil. For thicker films,Eis inversely proportional tot. Finally, the modulus approaches a lower asymptotic value whentis in excess of 20 mil. The results can be represented quantitatively by a model in which the surface transcrystalline region and the bulk phase of the polymer respond in a parallel combination to the applied stress. The modulus of the transcrystalline region in each polymer is higher than that of the bulk phase. The thickness of a surface region is about 12 &mgr; in polypropylene and 15 &mgr; in polyethylene. The effects of thermal history and the nature of the molded surface were examined briefly.

ISSN:0021-8979    

DOI:10.1063/1.1709938

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

For the determination of the trap depth from thermoluminescence and thermally stimuated current‐glow curves commonly the initial‐rise method by Garlick and Gibson is used. This method provides accurate results only if the conditionRh(T0)[2/z−1] ≤f(T0) is fulfilled.Ris the retrapping factor,zthe filling ratio of the traps at the temperatureT0,fthe concentration of unoccupied recombination centers, andhthe density of trapped electrons.

ISSN:0021-8979    

DOI:10.1063/1.1709939

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

The Seebeck coefficient of nonstoichiometric CoO was measured in the vicinity of the Ne´el temperature. A steep decrease in the Seebeck coefficient was found atTN. This decrease, as well as the change in the activation energy of conductivity atTNfound previously, can be explained either by a change in the ionization energy of the charge carriers or by a change of mobility activation energy.

ISSN:0021-8979    

DOI:10.1063/1.1709940

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

The volt‐ampere characteristics of Langmuir probes utilized in ionospheric investigations and employing ideal geometries (spherical or cylindrical) contain a considerable amount of information, much of which is not utilized in the usual analysis programs. The slope of theV‐icurve for large accelerating potentials contain a substantial amount of information on mass density and temperature. We have developed equations for the current and its slope in this region for both of the above geometries and have applied them to a few typical situations. We conclude that the usefulness of Langmuir‐probe techniques may be appreciably improved by performing a ``total analysis'' on the available information. In some cases, measuring the slope directly will supply the same information with a substantial saving in experimental complexity.

ISSN:0021-8979    

DOI:10.1063/1.1709941

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

No data existed as to the lower pressure limits of streamer breakdown in positive point‐to‐plane geometry. Using a combination of Lichtenberg figure techniques in the coplanar mode and a two‐photomultiplier analysis of the movement of luminous pulses between the electrodes, the streamer mechanism has been observed to 4 Torr in room air; below this pressure, it is too faint to observe. A primary streamer starts from the anode. Its speed of the order of 107cm/sec varies across the gap, depending on overvoltage and pressure. It is influenced by encounter with photoelectrically initiated avalanches from the cathode and by streamer‐tip‐cathode fields. On arrival at the cathode, fast space waves of potential gradient travel up the branch tips. Where such waves converge at the junction of the channel branches near the anode, a bright secondary streamer pulse appears. The tips of the midgap event move towards cathode and anode as secondary positive and negative streamers, respectively, at speeds around 106cm/sec. The luminosity engendered when the streamers are launched initiates a new negative photoelectrically triggered group of electron avalanches that move up the channel at about 106cm/sec. When this group meets the positive secondary streamer tip, the arc channel is completed. Observations leading to this picture constitute the content of this paper.

ISSN:0021-8979    

DOI:10.1063/1.1709943

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

The Voigt‐Reuss‐Hill (VRH) approximation, a useful scheme by which anisotropic single‐crystal elastic constants can be converted into isotropic polycrystalline elastic moduli, is shown to apply for moderately anisotropic cubic crystals like MgO, CaF2, &bgr;‐ZnS, ZnSe, and CdTe. Experimental values of polycrystalline isotropic elastic moduli for these materials are presented here, and the validity of the VRH approximation is established. The VRH approximation is then discussed for these materials with respect to their elastic anisotropy of crystals. To provide further support to this work, a numerical confirmation on the VRH moduli is made with the use of a high‐speed computer by calculating the mean velocity of sound in crystals and comparing this result with the corresponding quantity calculated from the actual polycrystalline elastic moduli. The general agreement is observed.

ISSN:0021-8979    

DOI:10.1063/1.1709944

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

Using a rate‐equation model, it is shown that the behavior of the saturable‐absorber giant‐pulse (SAGP) laser can be adequately described in terms of two parameters for values of the ratio of absorber to laser absorption cross section &sgr;>200:nai′ the normalized initial inversion and &sgr;&tgr;s, where &tgr;sis the normalized absorber relaxation time. In the general case, specification ofnai′, &sgr;, and &tgr;sis required. Theoretical curves of the giant‐pulse output power, energy, and rise‐ and falltimes are presented. The results are applicable in particular to SAGP lasers employing organic‐dye absorbers.

ISSN:0021-8979    

DOI:10.1063/1.1709945

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

The phenomenological theory of the electret effect, as developed by Wiseman and Feaster and extended by Perlman and Meunier, is cast into a form which allows a unified treatment of a variety of experiments. Introducing Mikusinski operators, a superposition principle expresses the electric displacement operator as &egr;E+PbwithPb(t)=−∞0&khgr;(t−T)E(T)dT,and &egr;=&egr;0+&khgr;i+&khgr;, where the operator &khgr; characterizes the slow polarization response and the constant &khgr;igives the fast response. Then, the fieldEwithin a dielectric of conductivitycis related to the electrode current densityJby the operator equationE=Z(J—J¯), whereZ=1/(c+s&egr;) determines the impedance operator and the operatorJ¯={dPb/dt}−&egr;iE(−0)gives the effects of fields applied beforet=0. Applications include a derivation of interesting relations discovered by Gross, an evaluation of the accuracy of the quasiequilibrium approximation used by Perlman and Meunier, and the construction of an equivalent circuit.

ISSN:0021-8979    

DOI:10.1063/1.1709946

出版商:AIP    

年代:1967

数据来源: AIP