Tungsten Oxide Mediated Quasi-van der Waals Epitaxy of WS₂ on Sapphire

Abstract

Conventional epitaxy plays a crucial role in current state-of-the art semiconductor technology, as it provides a path for accurate control at the atomic scale of thin films and nanostructures, to be used as the building blocks in nanoelectronics, optoelectronics, sensors, etc. Four decades ago, the terms "van der Waals" (vdW) and "quasi-vdW (Q-vdW) epitaxy" were coined to explain the oriented growth of vdW layers on 2D and 3D substrates, respectively. The major difference with conventional epitaxy is the weaker interaction between the epi-layer and the epi-substrates. Indeed, research on Q-vdW epitaxial growth of transition metal dichalcogenides (TMDCs) has been intense, with oriented growth of atomically thin semiconductors on sapphire being one of the most studied systems. Nonetheless, there are some striking and not yet understood differences in the literature regarding the orientation registry between the epi-layers and epi-substrate and the interface chemistry. Here we study the growth of WS 2 via a sequential exposure of the metal and the chalcogen precursors in a metal−organic chemical vapor deposition (MOCVD) system, introducing a metal-seeding step prior to the growth. The ability to control the delivery of the precursor made it possible to study the formation of a continuous and apparently ordered WO 3 mono-or few-layer at the surface of a c-plane sapphire. Such an interfacial layer is shown to strongly influence the subsequent quasi-vdW epitaxial growth of the atomically thin semiconductor layers on sapphire. Hence, here we elucidate an epitaxial growth mechanism and demonstrate the robustness of the metal-seeding approach for the oriented formation of other TMDC layers. This work may enable the rational design of vdW and quasi-vdW epitaxial growth on different material systems.

Large-area single-crystal TMD growth modulated by sapphire substrates

“…The traditional epitaxy growth requires high lattice matching (lattice mismatch requires less than 7%-8%) and strong chemical bonding between the epitaxial layer and the substrate. 38,39 Currently, there are van der Waals epitaxy, stepguided epitaxy, in-plane epitaxy and edge epitaxy, which have fewer requirements for lattice matching. 40 The main epitaxial mechanisms for growing TMDs on sapphire substrates are lattice-guided van der Waals epitaxy, step-guided epitaxy, and dual-coupling-guided epitaxy (Fig.…”

2D Materials in Flexible Electronics: Recent Advances and Future Prospectives

“…Additionally, a GaN semiconductor substrate (with lattice mismatch between GaN and MoS 2 under 1%) was used to orient the growth of monolayer MoS 2 . , The matching of the thermal expansion coefficients between GaN and MoS 2 enabled the synthesis of an unstrained MoS 2 film. C-sapphire wafers with a miscut angle toward the M axis (known as C/M) are commonly used as a substrate for commercial applications. − The steps of this type of wafer are parallel to the armchair (AC) edge of triangular TMD domains and the ⟨110⟩ direction. However, the close formation energies of antiparallel TMD domains along the AC edge may result in the formation of twin boundaries .…”

From monolayer to thin films: engineered bandgap in CVD grown Bi2Se(3−x)Sx topological insulator alloys

“…The implementation of practical electronic and optoelectronic devices requires repeatable growth of high-quality active materials with uniformity over large areas. In this context, chemical vapor deposition (CVD) is a well-known method for scalable deposition of transition metal dichalcogenides (TMDCs), 24,25 transition metal oxides (TMOs) such as waferscale single-layer amorphous MoO 3 , 26,27 and has also been demonstrated on chalcogenide optical materials. 28 CVD grown Bi 2 Se 3 crystals, with sizes up to 20 mm, were previously reported as well, 29 yet the synthesis of alloyed Bi 2 Se 3 has primarily relied on solution-processed techniques and molecular beam epitaxy (MBE).…”