Contact Properties on a Semiconducting MoTe₂ Crystal Using Polymorphic Structures

The strong Fermi level pinning (FLP) effect caused by the deposition of conventional metals is a crucial issue in field-effect transistors (FETs) based on transition metal dichalcogenides (TMDCs). In order to solve the problem, semimetal-polymorphic structures of a 1T′- and a 1T-MoTe2 have been used to make contact with the semiconducting phase of a 2H-MoTe2 channel. A 1T′/2H/1T′ polymorphic junction has been achieved by transferring the 1T′-MoTe2 at both ends of a 2H-MoTe2 crystal. This configuration demonstrates a high on/off ratio and a low contact resistance at room temperature for p-type FET operation. On the other hand, we found a laser-induced phase transition from 2H to 1T phase by irradiating a focused laser beam on MoTe2 crystals under vacuum conditions. By employing this technique, an in-plane 1T/2H/1T polymorphic junction has been achieved. The 1T phase contact exhibits Ohmic properties attributed to a pronounced heavy n-doping effect resulting from the high-density Te vacancies formed around the laser-irradiated region. The 1T phase contacted FET exhibits much better properties than the conventional metallic contact for n-type operation.