The Nernst and Ettingshausen effects in germanium single crystals of different conductivity type and with various impurity densities have been measured between 300 and 750°K in magnetic fields of 9000 gauss; the Nernst effect also at 2100 gauss. The experimental results are compared with theoretical expressions for the Nernst and Ettingshausen coefficients and with previously reported values for the thermal conductivity, which links the two effects through the Bridgman relationship. The qualitative agreement is very good, quantitative discrepancies are explained in terms of deviations of the sample mobilities from the theoretically assumed pure low-field lattice mobilities and by uncertainties in the numerical values used for the theoretical calculations. A derivation of the Nernst constant in the range of negligible phonon-drag effect is given, based on the analogy between thermo-and photomagnetoelectric effects. © A +
Measurements of the Seebeck coefficient on samples possessing resistivities between 1012 and 1014 Ω cm are accomplished by establishing a temperature difference between two electric contacts and reading the resulting voltage difference on a sensitive vibrating reed electrometer. Electrostatic pickup (through the ambient and gradient heating systems, the thermocouple leads, or from charges released through contact of the lead wires with a dielectric support) is eliminated in the most sensitive electrometer range by rigorous shielding procedures, which are described. The method was tested by measuring Seebeck coefficients between 30 and 80°C on metallo-organic ferrocene crystals of 0.5 mm thickness.
The photomagnetoelectric effect has been studied in germanium as a function of the wavelength of incident radiation in the region from 0.5 to 2.0 microns. The dependence of both photoconductivity and photomagnetoelectric (PME) response has been measured in various samples, using front and back surface recombination velocities and bulk recombination as parameters. It has been found that under certain conditions of bulk and surface recombination a reversal in sign for the PME response occurs over the frequency range studied. Sign reversals obtain at wavelength in the range from 1.55 to 1.85 microns, corresponding to partial optical transparency. The exact frequencies at which reversal occurs depend on the surface and bulk recombination rates, the condition being that the Dember field be zero corresponding to equal carrier concentrations on the front and back surfaces. Furthermore, the present observations are shown to be in good qualitative agreement with the theoretical work reported by Gartner. Experimental procedures are described, and it is shown how this effect can be used to advantage in the study of surface recombination velocities in various environments.
The establishment of a temperature distribution in a solid by optically excited diffusing and recombining carriers has been called the photothermal (PT) effect and has previously been described by the authors for certain special cases in semiconductors. The related effect with magnetic field is called the photomagnetothermal (PMT) effect. The paper gives a formulation of the theory governing the PMT effect and the case of weak magnetic fields and small temperature elevations in an infinite slab is worked out in detail. An apparatus for measuring the effect as a function of temperature is described and experimental data are presented, giving for the first time proof of the existence of this effect in germanium. Considering the experimental difficulties the agreement between theory and measurements is quite good.
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