Heteroepitaxial van der Waals semiconductors for atomically thin two-dimensional electronic circuitry
조문호 교수
포항공과대학교

We discuss a series of our recent works on epitaxial integration of van der Waals (vdW) semiconductors by atomic heteroepitaxy for atomically thin two-dimensional electronic circuitry. The first part is “the polymorphic heteroepitaxy”, where the distinct metallic and semiconducting atomic layer vdW crystals were stitched or stacked by a sequential metalorganic chemical vapor deposition [1-4]. It was verified that these polymorphic contacts are atomically coherent, showing the lowest contact barrier height ever-reported, which immediately contributed to the substantial outperformance of the epitaxial field-effect transistors (FETs) over conventional 2D FETs. The second part is “the epitaxial superlattices (SLs)”, in which more than two kinds of dissimilar vdW monolayer (ML) semiconductors were stacked by layer-by-layer sequential epitaxy with programmable stacking periodicities [5-6]. We have achieved this accurate ML-by-ML stacking by precise kinetics-controls in the near-equilibrium limit by metalorganic chemical vapor depositions, resulting in the tunable 2D vdW electronic systems. We discuss several atomic stacking orders at such vdW heterointerfaces, identified by various methods. These epitaxial vdW SLs are markedly different from conventional vdW heterostructures, realized by manual stacking processes, in that they can be a scalable quantum platform with atomic coherence. As an example, we demonstrate valley polarized carrier excitations - one of the most distinctive electronic features in vdW ML semiconductors, which scales with the stack numbers, upon optical excitations, by exploiting the series of type II band alignments at coherent heterointerfaces. References: [1] “Deterministic two-dimensional polymorphism growth of hexagonal n-type SnS2 and orthorhombic p-type SnS crystals”, Ji-Hoon Ahn et al., Nano Lett., 15, 3703 (2015). [2] “Interlayer orientation dependent light absorption and emission in monolayer semiconductor stacks”, Hoseok Heo et al., Nature Comm. 6, 7372 (2015). [3] “Coplanar semiconductor-metal circuitry defined on few-layer MoTe2 via polymorphic heteroepitaxy”, Ji Ho Sung et al., Nature Nanotechnol., 12, 1064, (2017). [4] “Epitaxial van der Waals contacts between transition-metal dichalcogenide monolayer polymorphs”, Chang-Soo Lee et al., Nano Letters, 19, 1814 (2019) [5] “Atomically thin three-dimensional membranes of van der Waals semiconductors by wafer-scale growth”, Gangtae Jin et al. Science Advances, 5, eaaw3180 (2019). [6] “Heteroepitaxial van der Waals semiconductor superlattices”, Gangtae Jin et al. Nature Nanotechnol. In Press (2021).