  Photodetectors with broadband optical response have promising applications in
many advanced optoelectronic and photonic devices. Especially, those with the
detection range up to mid-infrared at room temperature are very challenging and
highly desired. Recently, Weyl semimetal has been discovered and proposed to be
favorable for photodetection since in general it breaks Lorentz invariance to
have tilted chiral Weyl cones around Fermi level, which leads to chirality
dependent photocurrents at arbitrarily long wavelength. Furthermore, the linear
dispersion bands in Weyl cones result in very high carrier mobility and much
reduced thermal carrier compared with the parabolic ones in narrow-gap
semiconductors. Here, we report that the Weyl semimetal TaAs based
photodetector can operate at room temperature with spectral range from blue
(438.5 nm) to mid-infrared (10.29 {\mu}m) light wavelengths and the
responsibility and detectivity is more than 78 uA W-1 and 1.88*107 Jones,
respectively. This is the first photodetector made by a Weyl semimetal and
shows its promising in room-temperature mid-infrared photodetection.
