MoTe₂ Lateral Homojunction Field-Effect Transistors Fabricated using Flux-Controlled Phase Engineering

The coexistence of metallic and semiconducting polymorphs in transition-metal dichalcogenides (TMDCs) can be utilized to solve the large contact resistance issue in TMDC-based field effect transistors (FETs). A semiconducting hexagonal (2H) molybdenum ditelluride (MoTe₂) phase, metallic monoclinic (1T′) MoTe₂ phase, and their lateral homojunctions can be selectively synthesized in situ by chemical vapor deposition due to the small free energy difference between the two phases. Here, we have investigated, in detail, the structural and electrical properties of in situ-grown lateral 2H/1T′ MoTe₂ homojunctions grown using flux-controlled phase engineering. Using atomic-resolution plan-view and cross-sectional transmission electron microscopy analyses, we show that the round regions of near-single-crystalline 2H-MoTe₂ grow out of a polycrystalline 1T′-MoTe₂ matrix. We further demonstrate the operation of MoTe₂ FETs made on these in situ-grown lateral homojunctions with 1T′ contacts. The use of a 1T′ phase as electrodes in MoTe₂ FETs effectively improves the device performance by substantially decreasing the contact resistance. The contact resistance of 1T′ electrodes extracted from transfer length method measurements is 470 ± 30 ω·μm. Temperature- and gate-voltage-dependent transport characteristics reveal a flat-band barrier height of 30 ± 10 meV at the lateral 2H/1T′ interface that is several times smaller and shows a stronger gate modulation, compared to the metal/2H Schottky barrier height. The information learned from this analysis will be critical to understanding the properties of MoTe₂ homojunction FETs for use in memory and logic circuity applications.