Journal
JOURNAL OF CRYSTAL GROWTH
Volume 482, Issue -, Pages 61-69Publisher
ELSEVIER SCIENCE BV
DOI: 10.1016/j.jcrysgro.2017.10.024
Keywords
Molecular beam epitaxy; Tellurites; Semiconducting materials; X-ray diffraction
Funding
- Center for Low Energy Systems Technology (LEAST)
- MARCO
- DARPA
- NSF MRSEC program [DMR-1120296]
- National Science Foundation
- National Institutes of Health/National Institute of General Medical Sciences under NSF award [DMR-1332208]
- NSF Grant [DMR 1400432]
- NSF-EFRI 2DARE Grant [DMR 1433490]
- Emerging Frontiers & Multidisciplinary Activities
- Directorate For Engineering [1433490] Funding Source: National Science Foundation
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MoTe2 is the least explored material in the Molybdenum-chalcogen family. Molecular beam epitaxy (MBE) provides a unique opportunity to tackle the small electronegativity difference between Mo and Te while growing layer by layer away from thermodynamic equilibrium. We find that for a few-layer MoTe2 grown at a moderate rate of similar to 6 min per monolayer, a narrow window in temperature (above Te cell temperature) and Te:Mo ratio exists, where we can obtain pure phase 2H-MoTe2. This is confirmed using reflection high-energy electron diffraction (RHEED), Raman spectroscopy and X-ray photoemission spectroscopy (XPS). For growth on CaF2, Grazing incidence X-ray diffraction (GI-XRD) reveals a grain size of similar to 90 angstrom and presence of twinned grains. In this work, we hypothesis the presence of excess Te incorporation in MBE grown few layer 2H-MoTe2. For film on CaF2, it is based on >2 Te:Mo stoichiometry using XPS as well as a and c lattice spacing greater than bulk 2H-MoTe2. On GaAs, its based on observations of Te crystallite formation on film surface, 2 x 2 superstructure observed in RHEED and low energy electron diffraction, larger than bulk c-lattice spacing as well as the lack of electrical conductivity modulation by field effect. Finally, thermal stability and air sensitivity of MBE 2H-MoTe2 is investigated by temperature dependent XRD and XPS, respectively. (C) 2017 Elsevier B.V. All rights reserved.
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