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

Rui Ma; Huairuo Zhang; Youngdong Yoo; Zachary Patrick Degregorio; Lun Jin; Prafful Golani; Javad Ghasemi Azadani; Tony Low; James E Johns; Leonid A Bendersky; Albert V Davydov; Steven J Koester

doi:10.1021/acsnano.9b02785

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

ACS Nano. 2019 Jul 23;13(7):8035-8046. doi: 10.1021/acsnano.9b02785. Epub 2019 Jul 2.

Authors

Affiliations

¹ Department of Electrical and Computer Engineering , University of Minnesota , Minneapolis , Minnesota 55455 , United States.
² Theiss Research, Inc. , La Jolla , California 92037 , United States.
³ Materials Science and Engineering Division , National Institute of Standards and Technology (NIST) , Gaithersburg , Maryland 20899 , United States.
⁴ Department of Chemistry , Ajou University , Suwon 16499 , Korea.
⁵ Department of Chemistry , University of Minnesota , Minneapolis , Minnesota 55455 , United States.

PMID: 31247141
DOI: 10.1021/acsnano.9b02785

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 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.

Keywords: MoTe; Schottky barrier height; chemical vapor deposition; lateral homojunction; phase engineering; transition-metal dichalcogenide.