Large-area and few-layered 1T′-MoTe2 thin films grown by cold-wall chemical vapor deposition

Abstract

This study employs cold-wall chemical vapor deposition to achieve the growth of MoTe2 thin films on 4-inch sapphire substrates. A two-step growth process is utilized, incorporating MoO3 and Te powder sources under low-pressure conditions to synthesize MoTe2. The resultant MoTe2 thin films exhibit a dominant 1T′ phase, as evidenced by a prominent Raman peak at 161 cm−1. This preferential 1T′ phase formation is attributed to controlled manipulation of the second-step growth temperature, essentially the reaction stage between Te vapor and the pre-deposited MoO x layer. Under these optimized growth conditions, the thickness of the continuous 1T′-MoTe2 films can be precisely tailored within the range of 3.5–5.7 nm (equivalent to 5–8 layers), as determined by atomic force microscopy depth profiling. Hall-effect measurements unveil a typical hole concentration and mobility of 0.2 cm2 Vs−1 and 7.9 × 1021 cm−3, respectively, for the synthesized few-layered 1T′-MoTe2 films. Furthermore, Ti/Al bilayer metal contacts deposited on the few-layered 1T′-MoTe2 films exhibit low specific contact resistances of approximately 1.0 × 10−4 Ω cm2 estimated by the transfer length model. This finding suggests a viable approach for achieving low ohmic contact resistance using the 1T′-MoTe2 intermediate layer between metallic electrodes and two-dimensional semiconductors.