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

Abstract

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 <i><i>in situ</i></i> 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 <i>in situ</i>-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 <i>in situ</i>-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.