Passive terahertz source based on graded composition InGaAs structures

Ping-Keng Lu; Deniz Turan; Mona Jarrahi

doi:10.1117/12.2608882

7 March 2022 Passive terahertz source based on graded composition InGaAs structures

Ping-Keng Lu, Deniz Turan, Mona Jarrahi

Proceedings Volume 12000, Terahertz, RF, Millimeter, and Submillimeter-Wave Technology and Applications XV; 1200008 (2022) https://doi.org/10.1117/12.2608882
Event: SPIE OPTO, 2022, San Francisco, California, United States

Abstract

Terahertz sources that offer broadband radiation, compact footprint, and relatively low cost are mostly realized with photoconductive antennas built on a photo-absorbing substrate, where incident laser pulses generate electron-hole pairs and induce radiating ultrafast photocurrents. To create a strong field within the photoconductive active region and accelerate the photo-generated carriers, an external bias voltage is typically applied to the terahertz source to achieve high enough radiation power. However, with rapidly increasing interest for terahertz sources operating at 1550 nm - to take advantage of low-cost and compact fiber-based optics - it has become challenging to obtain high efficiency and at the same time overcome the degraded reliability due to the low resistivity and high dark current of photo-absorbing substrates at 1550 nm. To mitigate this challenge, we demonstrate a bias-free photoconductive terahertz source based on a graded composition InGaAs photoconductive layer, leading to completely passive optical-to-terahertz conversion with zero dark current. Using a linear gradient of Indium composition in a highly Be-doped InGaAs layer, a built-in electric field that extends deep into the substrate is created, leading to efficient collection of almost all optically generated electrons. Additionally, a large area plasmonic nanoantenna array is utilized to enhance the optical absorption at 1550 nm near each nanoantenna to reduce the average electron transit time to the radiating elements. With the graded InGaAs-based terahertz source, we experimentally demonstrate a 4-fold increase in radiation power compared to previously demonstrated passive plasmonic terahertz sources.

Conference Presentation

Citation Download Citation

Ping-Keng Lu, Deniz Turan, and Mona Jarrahi "Passive terahertz source based on graded composition InGaAs structures", Proc. SPIE 12000, Terahertz, RF, Millimeter, and Submillimeter-Wave Technology and Applications XV, 1200008 (7 March 2022); https://doi.org/10.1117/12.2608882

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