General criterion to distinguish between Schottky and Ohmic contacts at the metal/two-dimensional semiconductor interface

The contact interface plays a crucial role in the performance of various nanoelectronic devices based on two-dimensional (2D) semiconductors. Using first-principles calculations, we investigate the nature of single-layer titanium trisulfide (TiS₃) and metal contacts as a prototype system. We find that the contacts with Au(111), Ag(111), Al(111) and Cu(111) are of the Schottky type with barriers of 2.15, 1.67, 1.55 and 0.84 eV while that with Sc(111) is of a low-resistance Ohmic type. By comparing with several other typical 2D semiconductor-metal contacts, we propose that the contact type (i.e., Schottky or Ohmic) can be preliminarily identified according to the separation between the metal and the 2D semiconductor, which can be conveniently measured in experiments, with a critical value of ∼2.3 ± 0.2 Å.