Energy Efficient Terahertz Generation with GaN Photoconductive Emitters

Nontechnical description: Terahertz (THz) technology holds great potential for ultrahigh-bandwidth communication, non-intrusive medical and security imaging, and quantum materials spectroscopy. However, its widespread application is hindered by the lack of high-efficiency and high-power terahertz sources. One promising approach is the use of photoconductive THz emitters, which can, in principle, achieve an optical-to-THz power conversion efficiency beyond 100% by harnessing power from a DC electrical bias. Unfortunately, the physical properties of commonly used semiconductor materials for THz generation have low breakdown electrical field, restricting the realization of the THz generation efficiency. The project aims to develop innovative GaN-based terahertz (THz) photoconductive emitters with an optical-to-terahertz energy conversion efficiency approaching or even surpassing 100%. It leverages the unique properties of the wide bandgap GaN material, which exhibits a very large breakdown electrical field and a high saturation electron velocity. The project will also advance the understanding of photophysics, carrier dynamics, and THz coupling in wide bandgap GaN. In addition, it provides an active learning environment for graduate and undergraduate students, who will drive the frontier of science and technology in the future. Technical description: This project aims to enhance our fundamental understanding of the photophysics and ultrafast electron dynamics within GaN. Building upon this knowledge, the PI will design, characterize, and optimize highly efficient GaN photoconductive emitters with integrated THz nanoantennas. The research efforts will focus on three core directions: (I) Development of GaN photoconductive switches with a high breakdown electrical field approaching the intrinsic limit. (2) Investigation of ultrafast carrier dynamics, transient current, and THz generation in on-chip GaN THz devices. (3) Design and demonstration of energy-efficient and high-power free-space THz emitters. The proposed project will pave the way for energy-efficient THz emitters with an optical-to-THz energy conversion efficiency beyond 100%. Such power-efficient THz emitters hold the potential to facilitate the widespread adoption of novel THz technologies. Furthermore, this research will foster an interdisciplinary learning environment, providing graduate and undergraduate students with an opportunity to explore state-of-the-art nanofabrication, materials development, and advanced optical characterization techniques. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.