2 research outputs found
Rapid Wafer-Scale Growth of Polycrystalline 2H-MoS<sub>2</sub> by Pulsed Metal–Organic Chemical Vapor Deposition
High-volume
manufacturing of devices based on transition metal
dichalcogenide (TMD) ultrathin films will require deposition techniques
that are capable of reproducible wafer-scale growth with monolayer
control. To date, TMD growth efforts have largely relied upon sublimation
and transport of solid precursors with minimal control over vapor-phase
flux and gas-phase chemistry, which are critical for scaling up laboratory
processes to manufacturing settings. To address these issues, we report
a new pulsed metal–organic chemical vapor deposition (MOCVD)
route for MoS<sub>2</sub> film growth
in a research-grade single-wafer reactor. Using bisÂ(<i>tert</i>-butylimido)ÂbisÂ(dimethylamido)molybdenum and diethyl disulfide, we
deposit MoS<sub>2</sub> films from ∼1 nm to ∼25 nm in
thickness on SiO<sub>2</sub>/Si substrates. We show that layered 2H-MoS<sub>2</sub> can be produced at comparatively low reaction temperatures
of 591 °C at short deposition times, approximately 90 s for few-layer
films. In addition to the growth studies performed on SiO<sub>2</sub>/Si, films with wafer-level uniformity are demonstrated on 50 mm
quartz wafers. Process chemistry and impurity incorporation from precursors
are also discussed. This low-temperature and fast process highlights
the opportunities presented by metal–organic reagents in the
controlled synthesis of TMDs
Characterization of Few-Layer 1T′ MoTe<sub>2</sub> by Polarization-Resolved Second Harmonic Generation and Raman Scattering
We study the crystal
symmetry of few-layer 1T′ MoTe<sub>2</sub> using the polarization
dependence of the second harmonic
generation (SHG) and Raman scattering. Bulk 1T′ MoTe<sub>2</sub> is known to be inversion symmetric; however, we find that the inversion
symmetry is broken for finite crystals with even numbers of layers,
resulting in strong SHG comparable to other transition-metal dichalcogenides.
Group theory analysis of the polarization dependence of the Raman
signals allows for the definitive assignment of all the Raman modes
in 1T′ MoTe<sub>2</sub> and clears up a discrepancy in the
literature. The Raman results were also compared with density functional
theory simulations and are in excellent agreement with the layer-dependent
variations of the Raman modes. The experimental measurements also
determine the relationship between the crystal axes and the polarization
dependence of the SHG and Raman scattering, which now allows the anisotropy
of polarized SHG or Raman signal to independently determine the crystal
orientation