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

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.