Probing the photocurrent in two-dimensional titanium disulfide

Generating photocurrent in a condensed matter system involves the excitation, relaxation, and transportation of charge carriers. As such, it is viewed a potent method for probing the dynamics of non-equilibrium carriers and the electronic band structure of solid state materials. In this research, we analyze the photoresponse of the mechanically exfoliated titanium disulfide (TiS2), a transition metal dichalcogenide whose classification as either a semimetal or a semiconductor has been the subject of debate for years. The scanning photocurrent microscopy and the temperature-dependent photoresponse characterization expose the appearance of a photovoltaic current primarily from the metal/TiS2 junction in an unbiased sample, while negative photoconductivity due to the bolometric effect is observed in the conductive TiS2 channel. The optoelectronic experimental results, combined with electrical transport characterization and angle-resolved photoemission spectroscopy measurements, indicate that the TiS2 employed in this study is likely a heavily-doped semiconductor. Our findings unveil the photocurrent generation mechanism of two dimensional TiS2, highlighting its prospective optoelectronic applications in the future.