The Band Structure and Contact Issues of Quasi One Dimensional TiS₃

Titanium trisulfide (TiS₃) is a transition metal trichalcogenide whose atoms form chains of trigonal prisms creating a quasi-one-dimensional structure. This 1D structure results in an anisotropic band structure and edge perfection that can reduce the edge scattering effects experienced in sub 10 nm field-effect transistors. Furthermore, a recent theoretical study indicates that monolayer TiS₃ is a direct-gap semiconductor with a bandgap of ~1 eV and an electron mobility near 10,000 cm²V^-1s^-1 making TiS₃ an ideal candidate for high mobility transistors. Our recent work directly measured the in-plane anisotropy of few layer TiS₃ flakes using nanospot angle resolved photoemission spectroscopy. The effective hole mass at the top of the valence band was found to be -0.95 ± 0.09 m_e along the chain direction and -0.37 ± 0.1 m_e perpendicular to the chain direction. The measured mobility for TiS₃ transistors has remained well below the predicted value, but it is common for contact issues to lower the measured mobility. The interactions between TiS₃ and Au or Pt contacts have been investigated using x-ray photoemission spectroscopy which shows that strong bonding with sulfur is the key to prevent Schottky barrier formation.