  Here, we isolate thin TiS3 ribbons, a layered direct band gap semiconductor
(1.1 eV, well suited for detection all across the visible spectrum), thus far
almost unexplored. We fabricate field effect transistors and study their
electrical characteristics and optoelectronic properties. The measured FET
characteristics show mobilities up to 2.6 cm^2/Vs and ON/OFF ratios up to 10^4.
Under illumination, the TiS3 NR-FETs present an ultrahigh photoresponse of 2910
A/W and fast rise/fall times of ~4 ms. In addition, we measure cutoff
frequencies (f3dB) up to 1000 Hz. The strong combination of ultrahigh
sensitivity all along the visible spectrum and fast time response of TiS3
nanoribbon transistors put them among the best nanoscale photodetectors to
date.
