Sci. Adv. 4, eaao3057 (2018)

The realization of efficient and economical detectors that are sufficiently broadband to span the visible, infrared and terahertz (THz) wavelength regimes would be appealing. Now, Dong Wu and a team in China have made a detector from 1T-TaS2 (a 2D transition metal chalcogenide), which is responsive across this spectral range. And, it operates at room temperature. Unlike typical semiconductors, the 1T-TaS2 crystal, which consists of planes of hexagonally arranged tantalum atoms between two layers of sulfur atoms, exhibits strong reflectivity at low energy. The team made single crystals by chemical vapour transport in a sealed quartz tube; the process requires a quenching process to retain the 1T phase. Several-micrometre-thick exfoliated flakes had gold electrodes deposited on them and 780-μm-long (23-μm-wide) channels cut into them before transfer onto a sapphire substrate. The researchers claim that the detector’s 0.76 A W–1 responsivity at the THz wavelength of 118.8 μm is about two orders of magnitude better than that achieved with graphene-based broadband systems.