Low-resistivity Ohmic contacts of Ti/Al on few-layered 1T′-MoTe2/2H-MoTe2 heterojunctions grown by chemical vapor deposition†

Abstract

This study explores the phase-controlled growth of few-layered 2H-MoTe₂, 1T′-MoTe₂, and 2H-/1T′-MoTe₂ heterostructures and their impacts on metal contact properties. Cold-wall chemical vapor deposition (CW-CVD) with varying growth rates of MoO_x and reaction temperatures with Te vapors enabled the growth of continuous thin films of either 1T′-MoTe₂ or 2H-MoTe₂ phases on two-inch sapphire substrates. This methodology facilitates the meticulous optimization of chemical vapor deposition (CVD) parameters, enabling the realization of phase-controlled growth of few-layered MoTe₂ thin films and their subsequent heterostructures. The study further investigates the influence of a 1T′-MoTe₂ intermediate layer on the electrical properties of metal contacts on few-layered 2H-MoTe₂. Bi-layer Ti/Al contacts directly deposited on 2H-MoTe₂ exhibited Schottky behavior, indicating inefficient carrier transport. However, introducing a few-layered 1T′-MoTe₂ intermediate layer between the metal and 2H-MoTe₂ layers improved the contact characteristics significantly. The resulting Al/Ti/1T′-MoTe₂/2H-MoTe₂ contact scheme demonstrates Ohmic behavior with a specific contact resistance of around 1.7 × 10⁻⁴ Ω cm². This substantial improvement is attributed to the high carrier concentration of the 1T′-MoTe₂ intermediate layer which could be attributed tentatively to the increased tunneling events across the van der Waals gap and enhancing carrier transport between the metal and 2H-MoTe₂.