Properties of Surface Acoustic Waves in AlN And GaN
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Properties of Surface Acoustic Waves in AlN And GaN Jianyu Deng1, Daumantas Ciplys2,3, Gang Bu3, Michael Shur3, Remis Gaska1 Sensor Electronic Technology, Inc., 1195 Atlas Road, Columbia, SC 29209, U.S.A. 2 Department of Radiophysics, Vilnius University, Vilnius 2040, Lithuania 3 Department of Electrical, Computer, and Systems Engineering and Center for Integrated Elelectronics, Rensselaer Polytechnic Institute, Troy, NY 12180, U.S.A. 1
ABSTRACT The surface acoustic wave velocities, electromechanical coupling coefficients, and the spatial distributions of both elastic displacement and electric potential have been calculated for various configurations of gallium nitride and aluminum nitride. The electromechanical coupling coefficient values of 0.13 % in GaN and 0.29 % in AlN have been predicted. The maximum electromechanical coupling coefficient values of 0.24 % at Euler angles (0, 54o, 90o) in GaN and 1.08 % at (0, 53o, 90o) in AlN have been found. For GaN layer-on- sapphire substrate structures, the SAW velocity and electromechanical coupling coefficient have been calculated as functions of layer thickness and acoustic wavelength. The experimentally measured values of the surface acoustic wave velocity and electromechanical coupling coefficient are in satisfactory agreement with the calculation results.
INTRODUCTION Recent results on remote solar-blind sensors [1] and demonstration of acousto-optic diffraction [2] using surface acoustic wave (SAWs) have highlighted the importance of SAW in nitrides for novel acousto-opto-electronic device applications. The emergence of bulk AlN and GaN substrates has opened up a possibility to launch SAWs in GaN and AlN-based films with different crystallographic orientations. The calculation of basic SAW parameters such as velocity and electromechanical coupling coefficient for various orientations is of great importance for the design of AlGaN– based acousto-opto-electronic devices. In particular, the orientations of maximum SAW efficiency can be determined. In guided wave acoustooptics, the knowledge of the spatial distribution of elastic displacement and electric potential of the wave is necessary for the calculation of overlapping between acoustic and optical waves and finding conditions for the optimization of their interaction. We solved the wave propagation equations with appropriate boundary conditions and calculated the SAW velocity and electromechanical coupling coefficient in GaN and AlN substrates for various crystal orientations. For the GaN layer-onsapphire structure, the SAW velocity and electromechanical coupling coefficient have been calculated as functions of layer thickness and acoustic wavelength. The spatial variations of the SAW elastic displacement and electric potential have been calculated for both single substrate and layer-on-substrate configurations. The SAW velocity and electromechanical coupling coefficient have been measured in GaN-on-sapphire structure and are in good agreement with the calculated values.
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CALCULATION METHOD Con
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