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/TiS₂junction in an unbiased sample, while negative photoconductivity due to the bolometric effect is observed in the conductive TiS₂channel. The optoelectronic experimental results, combined with electrical transport characterization and angle-resolved photoemission spectroscopy measurements, indicate that the TiS₂employed 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.