Propagation of Leaky Waves in Free Surfaces and Grating Structures on (100)-Cut Gallium-Arsenide

118 p.Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 1987.The objective of the research described herein was to better understand the details of propagation of the leaky wave through metal grating structures in $\{$100$\}$-cut GaAs. This objective was met by first understanding wave propagation in free-surface GaAs and subsequently exploring a buried bimetallic electrode structure which will present minimum velocity and impedance perturbations to the wave. In this way, the free-surface diffraction theory may be used to accurately describe propagation through a metallic grating. We present a general method for measuring the surface acoustic wave (SAW) slowness surface on leaky-wave materials and a diffraction theory technique for predicting propagating beam profile shapes in unperturbed media. A modification to accommodate anisotropic loss is made to a method developed by Murray and Ash (8) for computing the SAW slowness surface of piezoelectric substrates. The resulting algorithm is used to determine the slowness surface for the leaky or pseudo-surface wave which propagates on $\{$100$\}$-cut GaAs and for a cut five degrees off from this. The data thus obtained are used in a diffraction theory computer program to predict the shape of beam profiles as they propagate in the substrate material, and accurate predictions of beam shapes are obtained. As the next logical step we address the problem of the propagation of a leaky wave through groove and metal grating structures on GaAs. Laser probe measurements are made, and a novel technique is used to discern the reflection coefficient of a grating as a function of angle of incidence of the leaky wave. From these data, the first-order mechanical scattering coefficients (FOMS) of the stripes of the grating are estimated, and it is determined that the nature of the leaky wave does not change so quickly with angle as to invalidate the assumptions inherent in the Datta and Hunsinger theory (12). Utilizing the theory developed by Datta and Hunsinger, a buried bimetallic electrode structure is designed which approaches a "perturbationless" grating. Several such gratings are constructed, and laser probe measurements demonstrate the attributes of the design.U of I OnlyRestricted to the U of I community idenfinitely during batch ingest of legacy ETD