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Dissertation Defense

Gallium Nitride Resonators for Infrared Detector Arrays and Resonant Acoustoelectric Amplifiers

Vikrant GokhalePhD Candidate

Gallium Nitride (GaN) is a popular semiconductor due to its uses in optics, RF, and power electronics. We explore a new dimension for GaN: high-frequency-micromechanical resonators. This thesis demonstrates one of the novel applications of GaN MEMS resonators, and investigates some of the fundamental electromechanical phenomena in this material.
We demonstrate the first monolithically integrated arrays of resonant infrared (IR) detectors using GaN. Single prototypes, sensor-reference pairs, and small-format detector arrays are successfully implemented with high sensitivity, low noise-equivalent-temperature, and fast response times. Such resonant detector arrays can be used as the imaging cores in high-performance uncooled IR cameras. To improve radiative absorption efficiency, we developed two novel thin-film IR absorber coatings: a broad-spectrum absorber using a carbon-nanotube nanocomposite and a selective narrow-spectrum absorber using plasmonic metamaterial gratings.
This work also presents the first measurements and analysis of an exciting, unexplored phenomenon: the amplification of acoustic standing waves in GaN resonators using electrical energy, boosting the quality factor (Q), and reducing energy losses in the resonator. This phenomenon is based on phonon-electron interactions in piezoelectric semiconductors. Normally, this interaction is a loss mechanism for acoustic energy, but we demonstrate that it can be reversed to provide acoustoelectric amplification and dynamic Q-amplification. The theory and experimental verification of this phenomena will be discussed in detail.

Sponsored by

Mina Rais-Zadeh, PhD