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Electrodeless techniques for semiconductor measurements and dimorphic phase transformations in compound semiconductors

University of British Columbia

Electrodeless techniques for semiconductor measurements, based on the inductive coupling of the sample to coils, are investigated in the first part of the thesis. The theory and the experimental techniques of two main experiments are developed and applied to several samples. The second part of the thesis is devoted to discussing dimorphic phase transformations in compound semiconductors. In the first experiment the sample is placed in the core of a solenoid which la excited by a sine wave generator. Eddy currents are induced in the sample and they set up a secondary magnetic field which opposes the primary field resulting in a decrease in flux through the core. The result is that a complex impedance is reflected into the coil. The increase in resistance and decrease in inductance of the coil is measured by a Q-meter technique and related to the conductivity for long cylindrical and spherical geometry samples. Design considerations are discussed, and it is shown that the optimum frequency to use, in order to obtain maximum sensitivity with the Q-meter, will depend on the conductivity of the material. Longitudinal and transverse magnatoresistance are observed by applying a static magnetic field along the appropriate axis of the solenoid. The second experiment is a crossed magnetic field determination of the Hall mobility. Circulating eddy currents are induced in the sample by a sinusoidally excited coil and a static magnetic field is applied along a second axis. The static field will rotate the plane of the eddy currents through the Hall angle, uHB, the product of the Hall mobility and the static field. The effect is the appearance of an alternating magnetic field along the third axle. This field, which at low frequencies is directly proportional to the Hall mobility, is detected by a second coil. The technique is very general and it is independent of the conductivity. In particular, it may be used to determine the Hall mobility of powders and liquids to which it is difficult or impossible to attach electrodes. In the second part of the thesis the compound semiconductor silver selenide is investigated. The sample could be obtained commercially only in powder form and hence the electrodeless techniques were essential. The temperature variation of conductivity above and below the phase transition, activation energies, relative conductivities at the phase transition and a conductivity-temperature hysteresis effect were observed. Absolute conductivity values were not obtained because of lack of knowledge of the radii of the individual powder grains and the Hall mobility measurements indicated that the sample was very impure, electronically speaking, and hence only impurity scattering was being measured.

Text

2011-12-08

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http://hdl.handle.net/2429/39559

Physics

University of British Columbia

Graduate