Acousto-Electric and Related Effects in Semiconductors at Microwave Frequencies

Price, David Harry Robert (1970) Acousto-Electric and Related Effects in Semiconductors at Microwave Frequencies. PhD thesis, University of Glasgow.

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This study is concerned with acousto-electric effects and the related phenomenon of acoustic attenuation, in semiconductors. An account is presented of a theory of acoustic amplification based on the diffusion-mobility approximation, for the case where the coupling between the acoustic wave and the conduction electrons is a function of the deformation potential of the material. Experimental results obtained for the amplification of a 9 GHz acoustic wave in germanium are compared with the predictions of this theory. These results, and others obtained in germanium by another worker, are found to be in agreement with the theoretical predictions provided the theoretical expression is correctly evaluated. In evaluating the expression it is necessary to recognise that certain of the quantities in the expression were electric field dependent under the experimental conditions. In order to obtain the required values of electron temperature and the other electric field dependent quantities, a series of measurements were made of Hall mobility as a function of electric field. This unusual method of obtaining values of the electron temperature, and its justification are considered. A review is included of the existing theories of the attenuation of microwave frequency acoustic waves in insulators at low temperatures. Special attention is paid to the temperature dependence and to the frequency dependence of the attenuation. The predictions of these theories are compared with the results of a series of attenuation measurements made in the temperature range 15-120 K, at frequencies of 1.0, 3.6 and 8.8 GHz. The measurements were made on three materials, zinc oxide, cadmium sulphide and cadmium selenide. An extensive comparison of theory and experiment is possible, and in all cases the theoretical predictions are verified. The study of acoustic attenuation was extended by a series of measurements made at room temperature in zinc oxide. The diffraction of a laser beam by an acoustic column was used as the basis of the method of measuring attenuation, rather than the pulse-echo technique used in the low temperature measurements. The method and its advantages are discussed, as is their experimental demonstration. The theories of the attenuation of acoustic waves at room temperature are discussed. Experimental results are presented which show that the attenuation of the longitudinal mode propagating along the c-axis of one specimen exhibited the anticipated frequency dependence; whereas the attenuation of the shear mode propagating parallel to the a-axis in another specimen did not show this dependence. An explanation of the behaviour of the attenuation in the shear specimen is presented. A number of experimental systems were used during the course of the work, each is described; as are the methods of preparing the different types of specimen used.

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Keywords: Electrical engineering
Date of Award: 1970
Depositing User: Enlighten Team
Unique ID: glathesis:1970-78533
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 28 Feb 2020 12:09
Last Modified: 28 Feb 2020 12:09

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