Growth And Electronic Transport Property Of Ultrothin MoS₂ And SnSe2/MoS₂ Van Der Waals Heterostructures

Two-dimensional (2D) materials have attracted considerable attention recently because of their unique structure and properties.Molybdenum disulfide (MoS2) as a typical transition metal dichalcogenide could overcome the limition of graphene (due to zero bandgap) in application of high-performance switch devices and high-gain optoelectronics etc. Here, chemical vapor deposition (CVD)was employed to fabricate ultrathin MoS2. On this basis, SnSe2/MoS2 heterostructures was growed by van der Waals epitaxial (vdW) technique and the interlayer coupling interaction were systematically investigated.The main results are acquired as follows:Firstly, high-quality MoS2 monolayers on SiO2/Si wafers were synthesized by CVD. The MoS2 monolayers with large lateral size have strong PL emission and high crystallinity. In addition, the back-gate FETs based on the as-grown MoS2 monolayers exhibit high on/off current ratio(～106) and carrier mobility (1.07 cm2 V-1S-1). The photodetector based on monolayer MoS2 is sensitive to laser with a wavelength of 532 nm. The external quantum efficiency is 548.Secondly, atomically thin MoS2 polycrystalline flakes were grown on high dielectric constant (high-k) substrates via CVD. The transmission electron microscope (TEM) and selected area electron diffraction (SAED)confirm the polycrystallinity of as-grown monolayer MoS2. Raman and PL spectra of the MoS2 depend on the substrates due to the optical interference. The interior layer of SiO2 is very important for enhancing the Raman and photoluminescence intensity; the Raman and PL intensity can also be improved by decreasing the thickness of HfO2 layer. In addition, the back-gate FETs based on the as-grown MoS2 flakes exhibit high on/off current ratio (～106) and carrier mobility (9.75 cm2 V-1 S-1).This work paves a way for controlled synthesis of high-quality ulthin 2D semiconductors on high-k substrates in furture.Thirdly, the ulthin SnSe2/MoS2 vdW heterostructures with a large lattice misfit have been synthesized by using a two-step CVD method.The high resolution TEM and SAED indicate that the heterostructures display well-aligned lattice orientation, that is, upper SnSe2 was synthesized by vdWs epitaxial growth. The interlayer coupling and charge transfer are observed in such two-dimensional heterostructures through micro Raman and photoluminescence spectroscopies. These results indicate that the SnSe2/MoS2 heterostructures have potential applications in electronics and optoelectronics.