Transition Metal Dichalcogenides (TMDCs) Heterostructures Field Effect Transistors (FETs) Fabricated by Sequential Chemical Vapor Deposition (CVD)

Abstract

Abstract Body: Transition metal dichalcogenides (TMDCs) are considered promising channel materials in future sub-5nm transistors due to their atomic-scale thickness, dangling bond-free surface and excellent electrical properties. However, the large contact resistance at the source/drain interface is still a critical issue that limits 2D TMDCs device performance. The contact resistance is affected by the Schottky barrier height (SBH) between the TMDC and the metal contact. Various contact engineering approaches have been explored to lower the SBH, such as optimizing the contact metals, chemical doping, plasma treatments, phase engineering, and others. One of the advantages of TMDCs in this regard is that many can exist in either a metallic or semiconducting phase, which, a property that can be used to. In our previous work, a lateral homojunction of semiconducting 2H-MoTe2 and metallic 1T’-MoTe2 was synthesized in-situ. FETs made on these homojunctions demonstrate an improvement of device performance due to substantially decreasing of the contact resistance compared to direct metal/2H contacts. Those results showed that the SBH of the 1T’/2H contact was much lower than the metal/2H interface. However, in-situ grown homojunctions lack controllability and scalability which limits its applications in TMDCs based devices. Here, we characterize sequential CVD techniques that can be generalized to any combination of TMDC materials. To date, we characterized sequentially-grown 1T’/2H homojunctions where the 1T’ material is MoTe2 and the 2H material is MoTe2, MoS2 and WS2. In all of these structures, the 2H material was first synthesized by CVD on a SiO2/Si substrate, then metallic 1T’-MoTe2 was synthesized by flux-controlled tellurization of molybdenum thin film. The technique shows capability of integration different TMDCs into heterostructures with controllability and compatibility with CMOS fabrication technique which is critical for both technological applications and fundamental sciences. The technique can both be applied to vertical or lateral heterostructures as well. In this paper, we will describe Raman spectra that show two distinct regions of TMDCs which indicates a successful integration of the differing TMDCs materials. We also describe FET made on the sequential-grown MoTe2 homojunctions, which show comparable electrical performance with the previously reported in-situ-grown MoTe2 homojunctions. 2H-MoS2/1T’-MoTe2 and 2H-WS2/1T’-MoTe2 heterostructures also show operational devices which indicates the potential to extend the technique to other TMDCs materials.