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Strain-induced photoconductive THz detectors for high-speed spectroscopy and imaging

D. Ponomarev 1, D. Lavrukhin 2, A. Yachmenev 1, R. Khabibullin 1, Yu. Goncharov 2, K. Zaytsev 2
1. V.G. Mokerov Institute of Ultra-High Frequency Semiconductor Electronics of the Russian Academy of Sciences, Moscow, Russia;
2. Prokhorov General Physics Institute of the Russian Academy of Sciences, Moscow, Russia


Photoconductive THz antennas (PCAs) are intensively used in modern time-domain spectroscopic and imaging setups thanks to their reliability, cost-effectiveness, simplicity of fabrication, and their flexibility in
the designing of antenna electrodes and topology, as well as the choice of photoconductive substrate. Compared with the existing THz devices [1,2], PCAs can efficiently work at room temperature demonstrating a broadband spectrum of 0.1-5.0 THz with a perfect dynamic range, i.e. signal-to-noise ratio exceeding even 100 dB [3]. Recently, the Ge-based PCAs have demonstrated an unprecedented bandwidth reaching 70 THz thanks to an absence of polar phonons in Ge [4]. Moreover, an optical-to-THz conversion efficiency of the PCA is not limited by the Manley-Rowe relation [5], as the photoconductivity theoretically allows converting every single optical photon into one electron-hole pair. Nevertheless, an increase of the spectrometer sensitivity, that is determined by the signal-to-noise ratio of a PCA-detector, is still in progress and requires additional solutions.

We report our recent approach on the new designed PCA-detector, that relies on the strain-induced InGaAs/InAlAs superlattice, providing an efficient operation at both 780 nm and 1550 nm laser excitation. In 2019 we proposed [6] that artificially strained SLs might be efficiently used for the PCA-detectors since they allow sub-picosecond photocarrier lifetimes with moderate mobility without using any compensating p-type dopants during fabrication. Then, we fabricated the PCA-detector and showed its advances over conventional (and commercial) detector that utilizes lattice-matched (LM) InGaAs/InAlAs SL [7]. The 3.5 THz detection bandwidth and signal-to-noise (S/N) ratio above 70 dB are reached. The strain-induced detector shows
quadratic dependence of its S/N ratio on probe beam power, while the S/N ratio for LM PCA-detector saturates at 5 mW. The first also demonstrates almost independent noise level of probe beam power, which is a crucial feature of the detector. We thus believe that strain-induced PCA-detector coupled to a fiber telecom wavelength laser, could open a pathway toward the development of portable and cost-effective THz photoconductive devices.

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Denis Lavrukhin
Prokhorov General Physics Institute of the Russian Academy of Sciences


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