title: Reversible Semiconducting-to-Metallic Phase Transition in Chemical Vapor Deposition Grown Monolayer WSe2 and Applications for Devices.
abstract: Two-dimensional (2D) semiconducting monolayer transition metal dichalcogenides (TMDCs) have stimulated lots of interest because they are direct bandgap materials that have reasonably good mobility values. However, contact between most metals and semiconducting TMDCs like 2H phase WSe2 are highly resistive, thus degrading the performance of field effect transistors (FETs) fabricated with WSe2 as active channel materials. Recently, a phase engineering concept of 2D MoS2 materials was developed, with improved device performance. Here, we applied this method to chemical vapor deposition (CVD) grown monolayer 2H-WSe2 and demonstrated semiconducting-to-metallic phase transition in atomically thin WSe2. We have also shown that metallic phase WSe2 can be converted back to semiconducting phase, demonstrating the reversibility of this phase transition. In addition, we fabricated FETs based on these CVD-grown WSe2 flakes with phase-engineered metallic 1T-WSe2 as contact regions and intact semiconducting 2H-WSe2 as active channel materials. The device performance is substantially improved with metallic phase source/drain electrodes, showing on/off current ratios of 10(7) and mobilities up to 66 cm(2)/V·s for monolayer WSe2. These results further suggest that phase engineering can be a generic strategy to improve device performance for many kinds of 2D TMDC materials.
authors.affiliation: Department of Electrical Engineering, University of Southern California, Los Angeles, California 90089, United States.
authors.forename: Yuqiang
authors.initials: Y
authors.lastname: Ma
authors.affiliation: Department of Electrical Engineering, University of Southern California, Los Angeles, California 90089, United States.
authors.forename: Bilu
authors.initials: B
authors.lastname: Liu
authors.affiliation: Department of Electrical Engineering, University of Southern California, Los Angeles, California 90089, United States.
authors.forename: Anyi
authors.initials: A
authors.lastname: Zhang
authors.affiliation: Department of Electrical Engineering, University of Southern California, Los Angeles, California 90089, United States.
authors.forename: Liang
authors.initials: L
authors.lastname: Chen
authors.affiliation: Department of Electrical Engineering, University of Southern California, Los Angeles, California 90089, United States.
authors.forename: Mohammad
authors.initials: M
authors.lastname: Fathi
authors.affiliation: Department of Electrical Engineering, University of Southern California, Los Angeles, California 90089, United States.
authors.forename: Chenfei
authors.initials: C
authors.lastname: Shen
authors.affiliation: Department of Electrical Engineering, University of Southern California, Los Angeles, California 90089, United States.
authors.forename: Ahmad N
authors.initials: AN
authors.lastname: Abbas
authors.affiliation: Department of Electrical Engineering, University of Southern California, Los Angeles, California 90089, United States.
authors.forename: Mingyuan
authors.initials: M
authors.lastname: Ge
authors.affiliation: Department of Electrical Engineering, University of Southern California, Los Angeles, California 90089, United States.
authors.forename: Matthew
authors.initials: M
authors.lastname: Mecklenburg
authors.affiliation: Department of Electrical Engineering, University of Southern California, Los Angeles, California 90089, United States.
authors.forename: Chongwu
authors.initials: C
authors.lastname: Zhou
keywords: contact; field effect transistor; mobility; phase engineering; transition metal dichalcogenides; tungsten diselenide; two-dimensional materials