Active Acoustic Emission From a Two-dimensional Electron Gas.

Surface Acoustic Wave;Two-dimensional Electron Gas;Gallium Nitride;High Electron Mobility Transistor;Piezoelectricity;Acoustoelectricity;Electrical Engineering;Mechanical Engineering;Engineering;Mechanical Engineering

Shao, LeiGrosh, Karl ;

University of Michigan

关键词: Surface Acoustic Wave;    Two-dimensional Electron Gas;    Gallium Nitride;    High Electron Mobility Transistor;    Piezoelectricity;    Acoustoelectricity;    Electrical Engineering;    Mechanical Engineering;    Engineering;    Mechanical Engineering;   

Others  :  https://deepblue.lib.umich.edu/bitstream/handle/2027.42/109039/shaolei_1.pdf?sequence=1&isAllowed=y

瑞士|英语

来源: The Illinois Digital Environment for Access to Learning and Scholarship

【 摘 要 】

This work examines the performance and fundamental operating principles of an active acoustic emitter based on an AlGaN/GaN high electron mobility transistor (HEMT). Strong piezoelectric effects in GaN-based semiconductors enable the formation of a two-dimensional electron gas (2DEG) that acts as the HEMT channel. Because of the strong coupling between 2DEG carrier density and mechanical deformation, HEMTs offer methods for active control of acoustic emission that are not possible with traditional passive emitters.First it is shown that intense surface acoustic waves (SAWs) are generated when the gate-source voltage is modulated at a high frequency that is resonant with the transistor geometry, due to the dynamic screening of the built-in strain in the AlGaN layer by the modulated 2DEG carrier density. The dynamic strain modulation generated during typical RF operation of an AlGaN/GaN based 2DEG is found to be two to three orders of magnitude higher than that generated by a conventional SAW emitter (interdigital transducer) at a similar size under the same RF operation.Next it is shown that the gate-source DC bias, which controls whether modulation occurs about a bias point at which the 2DEG is depleted or present, can be used to select the particular acoustic mode emitted. Finally it is shown that the drain-source DC bias can be used to control the directionality of acoustic emission through acoustoelectric amplification (or attenuation) of acoustic waves traveling in the same (or opposite) direction as the 2DEG electron drift current. In a measured HEMT, when an RF signal is applied across the gate/source electrodes to effect SAW generation in the presence of a DC bias across the drain/source, the ratio of SAW power emitted from the drain side to that from the source side reaches approximately 1.6 due to this effect.