title: Chemical Vapor Deposition Growth of Monolayer WSe2 with Tunable Device Characteristics and Growth Mechanism Study.
abstract: Semiconducting transition metal dichalcogenides (TMDCs) have attracted a lot of attention recently, because of their interesting electronic, optical, and mechanical properties. Among large numbers of TMDCs, monolayer of tungsten diselenides (WSe2) is of particular interest since it possesses a direct band gap and tunable charge transport behaviors, which make it suitable for a variety of electronic and optoelectronic applications. Direct synthesis of large domains of monolayer WSe2 and their growth mechanism studies are important steps toward applications of WSe2. Here, we report systematical studies on ambient pressure chemical vapor deposition (CVD) growth of monolayer and few layer WSe2 flakes directly on silica substrates. The WSe2 flakes were characterized using optical microscopy, atomic force microscopy, Raman spectroscopy, and photoluminescence spectroscopy. We investigated how growth parameters, with emphases on growth temperatures and durations, affect the sizes, layer numbers, and shapes of as-grown WSe2 flakes. We also demonstrated that transport properties of CVD-grown monolayer WSe2, similar to mechanically exfoliated samples, can be tuned into either p-type or ambipolar electrical behavior, depending on the types of metal contacts. These results deepen our understandings on the vapor phase growth mechanism of WSe2, and may benefit the uses of these CVD-grown monolayer materials in electronic and optoelectronics.
authors.affiliation: Ming Hsieh 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: Ming Hsieh 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: Ming Hsieh 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: Ming Hsieh Department of Electrical Engineering, University of Southern California, Los Angeles, California 90089, United States.
authors.forename: Ahmad
authors.initials: A
authors.lastname: Abbas
authors.affiliation: Ming Hsieh 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: Ming Hsieh Department of Electrical Engineering, University of Southern California, Los Angeles, California 90089, United States.
authors.forename: Chongwu
authors.initials: C
authors.lastname: Zhou
keywords: WSe2; ambipolar transport; chemical vapor deposition; growth mechanism; transition metal dichalcogenides; tungsten diselenides