We have observed emission of terahertz radiation from photoexcited GeS nanosheets without external bias. We attribute the origin of terahertz pulse emission to the shift current resulting from inversion symmetry breaking in ferroelectric single- or few-layer GeS nanosheets. We find that the direction of the shift current, and the corresponding polarity of the emitted THz pulses is determined by the spontaneous polarization in the ferroelectric GeS nanosheets. Experimental observation of zero-bias photocurrents puts GeS nanosheets forth as a promising candidate material for applications in third generation photovoltaics based on shift current, or bulk photovoltaic effect.
Kateryna Kushnir, Mengjing Wang, Patrick Fitzgerald, Kristie J. Koski, and Lyubov V. Titova, "Ultrafast zero-bias photocurrent in GeS nanosheets," Proc. SPIE 10530, Ultrafast Phenomena and Nanophotonics XXII, 105300Q (Presented at SPIE OPTO: January 30, 2018; Published: 22 February 2018); https://doi.org/10.1117/12.2291666.
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