Seed Crystal Homogeneity Controls Lateral and Vertical Heteroepitaxy of Monolayer MoS₂ and WS₂

Abstract

Heteroepitaxy between transition-metal dichalcogenide (TMDC) monolayers can fabricate atomically thin semiconductor heterojunctions without interfacial contamination, which are essential for next-generation electronics and optoelectronics. Here we report a controllable two-step chemical vapor deposition (CVD) process for lateral and vertical heteroepitaxy between monolayer WS2 and MoS2 on a c-cut sapphire substrate. Lateral and vertical heteroepitaxy can be selectively achieved by carefully controlling the growth of MoS2 monolayers that are used as two-dimensional (2D) seed crystals. Using hydrogen as a carrier gas, we synthesize ultraclean MoS2 monolayers, which enable lateral heteroepitaxial growth of monolayer WS2 from the MoS2 edges to create atomically coherent and sharp in-plane WS2/MoS2 heterojunctions. When no hydrogen is used, we obtain MoS2 monolayers decorated with small particles along the edges, inducing vertical heteroepitaxial growth of monolayer WS2 on top of the MoS2 to form vertical WS2/MoS2 heterojunctions. Our lateral and vertical atomic layer heteroepitaxy steered by seed defect engineering opens up a new route toward atomically controlled fabrication of 2D heterojunction architectures.

Atomic defect states in monolayers of MoS2 and WS2

“…These compounds can be synthesized through various methods, such as mechanical exfoliation 6 , chemical vapor deposition 7 , and intercalation techniques 8 . In addition, they have quite similar lattice constants which also enable the synthesis of MoS 2 -WS 2 heterostructures with minimum interfacial defects [9][10][11][12][13] .…”

Twinned growth behaviour of two-dimensional materials

“…We achieve 100% overlap for each of the stacked TMDCs structures, with crystal sizes of the heterostructures one order of magnitude larger than previous reports121314161820212223242526. For the twinned growth of ReS 2 /WS 2 vertical heterostructures, Au is chosen as the substrate and W–Re alloy foil is used as the Re and W sources, which lower the barrier energies for this special twinned growth process.…”

Metal Induced Growth of Transition Metal Dichalcogenides at Controlled Locations

“…Two-dimensional (2D) materials have attracted considerable interest due to their unique electrical, optical, thermal and mechanical properties that do not exist in their bulk form12345678910. Thus 2D materials are regarded as potential candidates for future logic devices11, integrated circuits12, and optoelectronics devices13.…”