Goldey, J. M.

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III. SOLID STATE PHYSICSProf. W. P. Allis Prof. G. G. Harvey J. M. GoldeyProf. S. C. Brown Prof. L. Tisza J. B. ThomasMICROWAVE STUDY OF SEMICONDUCTORSMeasurements of the carrier contribution to the dielectric coefficient of germaniumare under way. The dielectric coefficient is measured at a frequency of 24, 000 Mc/secby a waveguide transmission method. Details of the circuit are shown in Fig. III-1. Thebridge is balanced for a null at the detector with the sample in the circuit and then againwith a blank present. Power transmission is measured with the aid of the directionalcouplers and suitable detectors. The measurements give the complex transmissioncoefficient from which one may obtain the dielectric coefficient and conductivity of thesample (1).The carrier contribution to the dielectric coefficient is temperature-dependentthrough the temperature dependence of the mobility and carrier density. In the presentexperiment measurements are made between 2000K and 3000K. Throughout this tem-perature range, the carrier density for the samples used does not vary appreciably;hence, to a good approximation, changes in dielectric coefficient are the result ofchanges in mobility alone. One is then able to determine quite simply the effectivemass of the carriers involved from the change in carrier contribution with temperature.Measurements are being made on both n and p types of germanium with room tem-perature resistivities of the order of 5 ohm-cm. Three samples of each type are cutfrom adjacent portions of a single crystal. The samples are cut so that when they areplaced in the waveguide the electric field will be along the [100], [110], and [111] crystaldirections, respectively. The measurements are being made to determine whether orTOROS(Fig. III-1Schematic diagram of microwave bridge.-15-(III. SOLID STATE PHYSICS)not anisotropies in the carrier contributions (caused by anisotropies in either the effec-tive mass or collision frequency) will be observable in an experiment of this type. It isworth noting that for certain types of energy surfaces such anisotropies will not beobservable in this experiment.Measurements have been made on several samples and are in progress on the others.The results will be reported when complete.J. M. GoldeyReferences1. E. G. Montgomery, Techniques of Microwave Measurements (McGraw-Hill BookCompany, Inc., New York, 1947) Chap. 10.-16-

Solid State Physics

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Solid State Physics

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